Re: [PATCH V5 1/5] workqueues: Introduce new flag WQ_POWER_EFFICIENT for power oriented workqueues
>From cee22a15052faa817e3ec8985a28154d3fabc7aa Mon Sep 17 00:00:00 2001
From: Viresh Kumar
Date: Mon, 8 Apr 2013 16:45:40 +0530
Subject: workqueues: Introduce new flag WQ_POWER_EFFICIENT for power oriented
workqueues
Workqueues can be performance or power-oriented. Currently, most workqueues are
bound to the CPU they were created on. This gives good performance (due to cache
effects) at the cost of potentially waking up otherwise idle cores (Idle from
scheduler's perspective. Which may or may not be physically idle) just to
process some work. To save power, we can allow the work to be rescheduled on a
core that is already awake.
Workqueues created with the WQ_UNBOUND flag will allow some power savings.
However, we don't change the default behaviour of the system. To enable
power-saving behaviour, a new config option CONFIG_WQ_POWER_EFFICIENT needs to
be turned on. This option can also be overridden by the
workqueue.power_efficient boot parameter.
tj: Updated config description and comments. Renamed
CONFIG_WQ_POWER_EFFICIENT to CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
Signed-off-by: Viresh Kumar
Reviewed-by: Amit Kucheria
Signed-off-by: Tejun Heo
---
Documentation/kernel-parameters.txt | 15 +++
include/linux/workqueue.h | 27 +++
kernel/power/Kconfig| 20
kernel/workqueue.c | 13 +
4 files changed, 75 insertions(+)
diff --git a/Documentation/kernel-parameters.txt
b/Documentation/kernel-parameters.txt
index c3bfacb..37dfd72 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -3320,6 +3320,21 @@ bytes respectively. Such letter suffixes can also be
entirely omitted.
that this also can be controlled per-workqueue for
workqueues visible under /sys/bus/workqueue/.
+ workqueue.power_efficient
+ Per-cpu workqueues are generally preferred because
+ they show better performance thanks to cache
+ locality; unfortunately, per-cpu workqueues tend to
+ be more power hungry than unbound workqueues.
+
+ Enabling this makes the per-cpu workqueues which
+ were observed to contribute significantly to power
+ consumption unbound, leading to measurably lower
+ power usage at the cost of small performance
+ overhead.
+
+ The default value of this parameter is determined by
+ the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
+
x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
default x2apic cluster mode on platforms
supporting x2apic.
diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index 623488f..fc0136b 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -303,6 +303,33 @@ enum {
WQ_CPU_INTENSIVE= 1 << 5, /* cpu instensive workqueue */
WQ_SYSFS= 1 << 6, /* visible in sysfs, see
wq_sysfs_register() */
+ /*
+* Per-cpu workqueues are generally preferred because they tend to
+* show better performance thanks to cache locality. Per-cpu
+* workqueues exclude the scheduler from choosing the CPU to
+* execute the worker threads, which has an unfortunate side effect
+* of increasing power consumption.
+*
+* The scheduler considers a CPU idle if it doesn't have any task
+* to execute and tries to keep idle cores idle to conserve power;
+* however, for example, a per-cpu work item scheduled from an
+* interrupt handler on an idle CPU will force the scheduler to
+* excute the work item on that CPU breaking the idleness, which in
+* turn may lead to more scheduling choices which are sub-optimal
+* in terms of power consumption.
+*
+* Workqueues marked with WQ_POWER_EFFICIENT are per-cpu by default
+* but become unbound if workqueue.power_efficient kernel param is
+* specified. Per-cpu workqueues which are identified to
+* contribute significantly to power-consumption are identified and
+* marked with this flag and enabling the power_efficient mode
+* leads to noticeable power saving at the cost of small
+* performance disadvantage.
+*
+* http://thread.gmane.org/gmane.linux.kernel/1480396
+*/
+ WQ_POWER_EFFICIENT = 1 << 7,
+
__WQ_DRAINING = 1 << 16, /* internal: workqueue is draining */
__WQ_ORDERED= 1 << 17, /* internal: workqueue is ordered */
diff --git a/kernel/power/Kconfig b/kernel/power/Kconfig
index 5dfdc9e..4645596 100644
--- a/kernel/power/Kconfig
+++ b/kernel/power/Kconfig
Re: [PATCH V5 1/5] workqueues: Introduce new flag WQ_POWER_EFFICIENT for power oriented workqueues
From cee22a15052faa817e3ec8985a28154d3fabc7aa Mon Sep 17 00:00:00 2001
From: Viresh Kumar viresh.ku...@linaro.org
Date: Mon, 8 Apr 2013 16:45:40 +0530
Subject: workqueues: Introduce new flag WQ_POWER_EFFICIENT for power oriented
workqueues
Workqueues can be performance or power-oriented. Currently, most workqueues are
bound to the CPU they were created on. This gives good performance (due to cache
effects) at the cost of potentially waking up otherwise idle cores (Idle from
scheduler's perspective. Which may or may not be physically idle) just to
process some work. To save power, we can allow the work to be rescheduled on a
core that is already awake.
Workqueues created with the WQ_UNBOUND flag will allow some power savings.
However, we don't change the default behaviour of the system. To enable
power-saving behaviour, a new config option CONFIG_WQ_POWER_EFFICIENT needs to
be turned on. This option can also be overridden by the
workqueue.power_efficient boot parameter.
tj: Updated config description and comments. Renamed
CONFIG_WQ_POWER_EFFICIENT to CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
Signed-off-by: Viresh Kumar viresh.ku...@linaro.org
Reviewed-by: Amit Kucheria amit.kuche...@linaro.org
Signed-off-by: Tejun Heo t...@kernel.org
---
Documentation/kernel-parameters.txt | 15 +++
include/linux/workqueue.h | 27 +++
kernel/power/Kconfig| 20
kernel/workqueue.c | 13 +
4 files changed, 75 insertions(+)
diff --git a/Documentation/kernel-parameters.txt
b/Documentation/kernel-parameters.txt
index c3bfacb..37dfd72 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -3320,6 +3320,21 @@ bytes respectively. Such letter suffixes can also be
entirely omitted.
that this also can be controlled per-workqueue for
workqueues visible under /sys/bus/workqueue/.
+ workqueue.power_efficient
+ Per-cpu workqueues are generally preferred because
+ they show better performance thanks to cache
+ locality; unfortunately, per-cpu workqueues tend to
+ be more power hungry than unbound workqueues.
+
+ Enabling this makes the per-cpu workqueues which
+ were observed to contribute significantly to power
+ consumption unbound, leading to measurably lower
+ power usage at the cost of small performance
+ overhead.
+
+ The default value of this parameter is determined by
+ the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
+
x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
default x2apic cluster mode on platforms
supporting x2apic.
diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index 623488f..fc0136b 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -303,6 +303,33 @@ enum {
WQ_CPU_INTENSIVE= 1 5, /* cpu instensive workqueue */
WQ_SYSFS= 1 6, /* visible in sysfs, see
wq_sysfs_register() */
+ /*
+* Per-cpu workqueues are generally preferred because they tend to
+* show better performance thanks to cache locality. Per-cpu
+* workqueues exclude the scheduler from choosing the CPU to
+* execute the worker threads, which has an unfortunate side effect
+* of increasing power consumption.
+*
+* The scheduler considers a CPU idle if it doesn't have any task
+* to execute and tries to keep idle cores idle to conserve power;
+* however, for example, a per-cpu work item scheduled from an
+* interrupt handler on an idle CPU will force the scheduler to
+* excute the work item on that CPU breaking the idleness, which in
+* turn may lead to more scheduling choices which are sub-optimal
+* in terms of power consumption.
+*
+* Workqueues marked with WQ_POWER_EFFICIENT are per-cpu by default
+* but become unbound if workqueue.power_efficient kernel param is
+* specified. Per-cpu workqueues which are identified to
+* contribute significantly to power-consumption are identified and
+* marked with this flag and enabling the power_efficient mode
+* leads to noticeable power saving at the cost of small
+* performance disadvantage.
+*
+* http://thread.gmane.org/gmane.linux.kernel/1480396
+*/
+ WQ_POWER_EFFICIENT = 1 7,
+
__WQ_DRAINING = 1 16, /* internal: workqueue is draining */
__WQ_ORDERED= 1 17, /* internal: workqueue is ordered */
diff --git a/kernel/power/Kconfig b/kernel/power/Kconfig
index
Re: [PATCH V5 1/5] workqueues: Introduce new flag WQ_POWER_EFFICIENT for power oriented workqueues
On 27 April 2013 00:41, Tejun Heo wrote: > > It's already too late for the upcoming merge window, but things > generally look good to me and I'll apply the patchset once wq/for-3.11 > opens. One nitpick tho. > > On Thu, Apr 25, 2013 at 09:13:44AM +0530, Viresh Kumar wrote: >> + workqueue.power_efficient >> + Workqueues can be performance or power-oriented. >> + Currently, most workqueues are bound to the CPU they > >per-cpu would be better > >> + were created on. This gives good performance (due to >> + cache effects) at the cost of potentially waking up >> + otherwise idle cores just to process some work. To save >> + power, we can allow the work to be rescheduled on a >> core >> + that is already awake. > > The above description is confusing to me. As have been discussed > multiple times before, per-cpu workqueue in itself doesn't wake up the > CPU physically. The timer may but per-cpu workqueue doesn't. It was > confusing when this patchset was first posted and the above phrasing > is still confusing. What the patchset tries to do is preventing the > scheduler from perceiving the CPU as active due to the activated > worker thread pinned to that CPU, right? The knob doesn't really do > anything about waking up the processor in itself. It just avoids > feeding the scheduler with noisy activation events and allows it to > allocate work item execution according to the scheduler's view of CPU > active/idleness. As the scheduler has longer / larger scope of > overall CPU activities and means to regulate them, this leads to more > power-efficient allocation of work item executions, right? It'd be > really great if the descriptions and the comment above the flag makes > this abundantly clear because it's not something too apparent. Sorry for the long delay for such a small change. I went on long leaves.. I have added following to make things more clear at places: (Idle from scheduler's perspective. Which may or may not be physically idle).. Let me know if it is still unclear.. And this is the new patch: (Attached it too for applying cleanly) -x---x--- From: Viresh Kumar Date: Mon, 8 Apr 2013 16:45:40 +0530 Subject: [PATCH V5 resent 1/5] workqueues: Introduce new flag WQ_POWER_EFFICIENT for power oriented workqueues Workqueues can be performance or power-oriented. Currently, most workqueues are bound to the CPU they were created on. This gives good performance (due to cache effects) at the cost of potentially waking up otherwise idle cores (Idle from scheduler's perspective. Which may or may not be physically idle) just to process some work. To save power, we can allow the work to be rescheduled on a core that is already awake. Workqueues created with the WQ_UNBOUND flag will allow some power savings. However, we don't change the default behaviour of the system. To enable power-saving behaviour, a new config option CONFIG_WQ_POWER_EFFICIENT needs to be turned on. This option can also be overridden by the workqueue.power_efficient boot parameter. Signed-off-by: Viresh Kumar Reviewed-by: Amit Kucheria --- Documentation/kernel-parameters.txt | 18 ++ include/linux/workqueue.h | 3 +++ kernel/power/Kconfig| 21 + kernel/workqueue.c | 11 +++ 4 files changed, 53 insertions(+) diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index c3bfacb..9a991b6 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -3320,6 +3320,24 @@ bytes respectively. Such letter suffixes can also be entirely omitted. that this also can be controlled per-workqueue for workqueues visible under /sys/bus/workqueue/. + workqueue.power_efficient + Workqueues can be performance or power-oriented. + Currently, most workqueues are bound to the CPU they + were created on. This gives good performance (due to + cache effects) at the cost of potentially waking up + otherwise idle cores (Idle from scheduler's perspective. + Which may or may not be physically idle) just to process + some work. To save power, we can allow the work to be + rescheduled on a core that is already awake. + + Workqueues created with the WQ_UNBOUND flag will allow + some power savings. However, we don't change the + default behaviour of the system. To enable power-saving + behaviour, a new config option CONFIG_WQ_POWER_EFFICIENT
Re: [PATCH V5 1/5] workqueues: Introduce new flag WQ_POWER_EFFICIENT for power oriented workqueues
On 27 April 2013 00:41, Tejun Heo t...@kernel.org wrote: It's already too late for the upcoming merge window, but things generally look good to me and I'll apply the patchset once wq/for-3.11 opens. One nitpick tho. On Thu, Apr 25, 2013 at 09:13:44AM +0530, Viresh Kumar wrote: + workqueue.power_efficient + Workqueues can be performance or power-oriented. + Currently, most workqueues are bound to the CPU they per-cpu would be better + were created on. This gives good performance (due to + cache effects) at the cost of potentially waking up + otherwise idle cores just to process some work. To save + power, we can allow the work to be rescheduled on a core + that is already awake. The above description is confusing to me. As have been discussed multiple times before, per-cpu workqueue in itself doesn't wake up the CPU physically. The timer may but per-cpu workqueue doesn't. It was confusing when this patchset was first posted and the above phrasing is still confusing. What the patchset tries to do is preventing the scheduler from perceiving the CPU as active due to the activated worker thread pinned to that CPU, right? The knob doesn't really do anything about waking up the processor in itself. It just avoids feeding the scheduler with noisy activation events and allows it to allocate work item execution according to the scheduler's view of CPU active/idleness. As the scheduler has longer / larger scope of overall CPU activities and means to regulate them, this leads to more power-efficient allocation of work item executions, right? It'd be really great if the descriptions and the comment above the flag makes this abundantly clear because it's not something too apparent. Sorry for the long delay for such a small change. I went on long leaves.. I have added following to make things more clear at places: (Idle from scheduler's perspective. Which may or may not be physically idle).. Let me know if it is still unclear.. And this is the new patch: (Attached it too for applying cleanly) -x---x--- From: Viresh Kumar viresh.ku...@linaro.org Date: Mon, 8 Apr 2013 16:45:40 +0530 Subject: [PATCH V5 resent 1/5] workqueues: Introduce new flag WQ_POWER_EFFICIENT for power oriented workqueues Workqueues can be performance or power-oriented. Currently, most workqueues are bound to the CPU they were created on. This gives good performance (due to cache effects) at the cost of potentially waking up otherwise idle cores (Idle from scheduler's perspective. Which may or may not be physically idle) just to process some work. To save power, we can allow the work to be rescheduled on a core that is already awake. Workqueues created with the WQ_UNBOUND flag will allow some power savings. However, we don't change the default behaviour of the system. To enable power-saving behaviour, a new config option CONFIG_WQ_POWER_EFFICIENT needs to be turned on. This option can also be overridden by the workqueue.power_efficient boot parameter. Signed-off-by: Viresh Kumar viresh.ku...@linaro.org Reviewed-by: Amit Kucheria amit.kuche...@linaro.org --- Documentation/kernel-parameters.txt | 18 ++ include/linux/workqueue.h | 3 +++ kernel/power/Kconfig| 21 + kernel/workqueue.c | 11 +++ 4 files changed, 53 insertions(+) diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index c3bfacb..9a991b6 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -3320,6 +3320,24 @@ bytes respectively. Such letter suffixes can also be entirely omitted. that this also can be controlled per-workqueue for workqueues visible under /sys/bus/workqueue/. + workqueue.power_efficient + Workqueues can be performance or power-oriented. + Currently, most workqueues are bound to the CPU they + were created on. This gives good performance (due to + cache effects) at the cost of potentially waking up + otherwise idle cores (Idle from scheduler's perspective. + Which may or may not be physically idle) just to process + some work. To save power, we can allow the work to be + rescheduled on a core that is already awake. + + Workqueues created with the WQ_UNBOUND flag will allow + some power savings. However, we don't change the + default behaviour of the system. To enable power-saving + behaviour, a
Re: [PATCH V5 1/5] workqueues: Introduce new flag WQ_POWER_EFFICIENT for power oriented workqueues
On 29 April 2013 21:49, Tejun Heo wrote: > On Mon, Apr 29, 2013 at 12:06:28PM +0530, Viresh Kumar wrote: > Yeap, !WQ_UNBOUND workqueues == per-cpu workqueues. Sigh!! You were talking about thread per cpu here... Sorry for missing it earlier :( >> At this time local cpu may be busy or idle (Atleast according to scheduler). >> We don't want a idle cpu (From schedulers perspective) to be used for >> running this work's handler due to two reasons. >> - idle cpu may be in WFI or deeper idle states and so we can avoid waking >> it up. > > I have no idea what WFI is but the physical CPU is already awake at > that time. It can't be idle - it's running queue_work(). It could be > running in lower freq tho, which each code piece doesn't really have > much control over. Stupid point. WFI: Wait for interrupt (low power mode of cpu). >> - We will make idle cpu look busy and so other kernel stuff may be scheduled >> on it now. But we could have kept it idle for a long time. > > Hmmm... yeah, about the same thing I wrote, it's not really about not > waking up the CPU right now physically but avoiding forcing the > scheduler scheduling a pinned task on an otherwise quiescent CPU. > This effectively allows the scheduler to migrate such work items > towards a CPU which the scheduler considers to be better (in power or > whatever) leading to noticeable powersave. Correct. >> And what timer are you talking about? I am not talking about deffered work >> only, >> but normal work too. > > Deferred work item == timer + work item. Ya, i knew that :) >> I might have wrongly phrased some part of my patch (maybe used workqueue >> instead of work), will fix that up. > > I think it'd be necessary to distinguish the physical CPU being idle > and the scheduler considers it to be idle (no task to schedule on it) > and explain how increasing the latter can lead to powersave. As it's > currently written, it seemingly, to me anyway, suggests that the > proposed change somehow avoids waking up actually idle CPU, which > isn't the case as queue_work() *always* schedules on the local CPU. > The local CPU can't be idle by definition. Yes you are correct. I will fix it. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH V5 1/5] workqueues: Introduce new flag WQ_POWER_EFFICIENT for power oriented workqueues
Hello, On Mon, Apr 29, 2013 at 12:06:28PM +0530, Viresh Kumar wrote: > Whatever you wrote above confused me even more :) Heh heh, confumageddon > This is what i had in my mind until now. Its not about per-cpu workqueue. > > Lets take example of system_wq. It doesn't have WQ_UNBOUND flag set. > Now if we call queue_work_on() with cpu x and sytem_wq, then work > will execute on cpu x. If we call queue_work() then it will queue the work > on local cpu. Yeap, !WQ_UNBOUND workqueues == per-cpu workqueues. > At this time local cpu may be busy or idle (Atleast according to scheduler). > We don't want a idle cpu (From schedulers perspective) to be used for > running this work's handler due to two reasons. > - idle cpu may be in WFI or deeper idle states and so we can avoid waking > it up. I have no idea what WFI is but the physical CPU is already awake at that time. It can't be idle - it's running queue_work(). It could be running in lower freq tho, which each code piece doesn't really have much control over. > - We will make idle cpu look busy and so other kernel stuff may be scheduled > on it now. But we could have kept it idle for a long time. Hmmm... yeah, about the same thing I wrote, it's not really about not waking up the CPU right now physically but avoiding forcing the scheduler scheduling a pinned task on an otherwise quiescent CPU. This effectively allows the scheduler to migrate such work items towards a CPU which the scheduler considers to be better (in power or whatever) leading to noticeable powersave. > And what timer are you talking about? I am not talking about deffered work > only, > but normal work too. Deferred work item == timer + work item. > I might have wrongly phrased some part of my patch (maybe used workqueue > instead of work), will fix that up. I think it'd be necessary to distinguish the physical CPU being idle and the scheduler considers it to be idle (no task to schedule on it) and explain how increasing the latter can lead to powersave. As it's currently written, it seemingly, to me anyway, suggests that the proposed change somehow avoids waking up actually idle CPU, which isn't the case as queue_work() *always* schedules on the local CPU. The local CPU can't be idle by definition. Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH V5 1/5] workqueues: Introduce new flag WQ_POWER_EFFICIENT for power oriented workqueues
Hey Tejun, On 27 April 2013 00:41, Tejun Heo wrote: > Hey, Viresh. > > It's already too late for the upcoming merge window, but things > generally look good to me and I'll apply the patchset once wq/for-3.11 > opens. One nitpick tho. Obviously. I understand this and agree with you on it. It should go in 3.11 now. > On Thu, Apr 25, 2013 at 09:13:44AM +0530, Viresh Kumar wrote: >> + workqueue.power_efficient >> + Workqueues can be performance or power-oriented. >> + Currently, most workqueues are bound to the CPU they > >per-cpu would be better > >> + were created on. This gives good performance (due to >> + cache effects) at the cost of potentially waking up >> + otherwise idle cores just to process some work. To save >> + power, we can allow the work to be rescheduled on a >> core >> + that is already awake. > > The above description is confusing to me. As have been discussed > multiple times before, per-cpu workqueue in itself doesn't wake up the > CPU physically. The timer may but per-cpu workqueue doesn't. It was > confusing when this patchset was first posted and the above phrasing > is still confusing. What the patchset tries to do is preventing the > scheduler from perceiving the CPU as active due to the activated > worker thread pinned to that CPU, right? The knob doesn't really do > anything about waking up the processor in itself. It just avoids > feeding the scheduler with noisy activation events and allows it to > allocate work item execution according to the scheduler's view of CPU > active/idleness. As the scheduler has longer / larger scope of > overall CPU activities and means to regulate them, this leads to more > power-efficient allocation of work item executions, right? It'd be > really great if the descriptions and the comment above the flag makes > this abundantly clear because it's not something too apparent. Whatever you wrote above confused me even more :) This is what i had in my mind until now. Its not about per-cpu workqueue. Lets take example of system_wq. It doesn't have WQ_UNBOUND flag set. Now if we call queue_work_on() with cpu x and sytem_wq, then work will execute on cpu x. If we call queue_work() then it will queue the work on local cpu. At this time local cpu may be busy or idle (Atleast according to scheduler). We don't want a idle cpu (From schedulers perspective) to be used for running this work's handler due to two reasons. - idle cpu may be in WFI or deeper idle states and so we can avoid waking it up. - We will make idle cpu look busy and so other kernel stuff may be scheduled on it now. But we could have kept it idle for a long time. And what timer are you talking about? I am not talking about deffered work only, but normal work too. I might have wrongly phrased some part of my patch (maybe used workqueue instead of work), will fix that up. -- viresh -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH V5 1/5] workqueues: Introduce new flag WQ_POWER_EFFICIENT for power oriented workqueues
Hey Tejun, On 27 April 2013 00:41, Tejun Heo t...@kernel.org wrote: Hey, Viresh. It's already too late for the upcoming merge window, but things generally look good to me and I'll apply the patchset once wq/for-3.11 opens. One nitpick tho. Obviously. I understand this and agree with you on it. It should go in 3.11 now. On Thu, Apr 25, 2013 at 09:13:44AM +0530, Viresh Kumar wrote: + workqueue.power_efficient + Workqueues can be performance or power-oriented. + Currently, most workqueues are bound to the CPU they per-cpu would be better + were created on. This gives good performance (due to + cache effects) at the cost of potentially waking up + otherwise idle cores just to process some work. To save + power, we can allow the work to be rescheduled on a core + that is already awake. The above description is confusing to me. As have been discussed multiple times before, per-cpu workqueue in itself doesn't wake up the CPU physically. The timer may but per-cpu workqueue doesn't. It was confusing when this patchset was first posted and the above phrasing is still confusing. What the patchset tries to do is preventing the scheduler from perceiving the CPU as active due to the activated worker thread pinned to that CPU, right? The knob doesn't really do anything about waking up the processor in itself. It just avoids feeding the scheduler with noisy activation events and allows it to allocate work item execution according to the scheduler's view of CPU active/idleness. As the scheduler has longer / larger scope of overall CPU activities and means to regulate them, this leads to more power-efficient allocation of work item executions, right? It'd be really great if the descriptions and the comment above the flag makes this abundantly clear because it's not something too apparent. Whatever you wrote above confused me even more :) This is what i had in my mind until now. Its not about per-cpu workqueue. Lets take example of system_wq. It doesn't have WQ_UNBOUND flag set. Now if we call queue_work_on() with cpu x and sytem_wq, then work will execute on cpu x. If we call queue_work() then it will queue the work on local cpu. At this time local cpu may be busy or idle (Atleast according to scheduler). We don't want a idle cpu (From schedulers perspective) to be used for running this work's handler due to two reasons. - idle cpu may be in WFI or deeper idle states and so we can avoid waking it up. - We will make idle cpu look busy and so other kernel stuff may be scheduled on it now. But we could have kept it idle for a long time. And what timer are you talking about? I am not talking about deffered work only, but normal work too. I might have wrongly phrased some part of my patch (maybe used workqueue instead of work), will fix that up. -- viresh -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH V5 1/5] workqueues: Introduce new flag WQ_POWER_EFFICIENT for power oriented workqueues
Hello, On Mon, Apr 29, 2013 at 12:06:28PM +0530, Viresh Kumar wrote: Whatever you wrote above confused me even more :) Heh heh, confumageddon This is what i had in my mind until now. Its not about per-cpu workqueue. Lets take example of system_wq. It doesn't have WQ_UNBOUND flag set. Now if we call queue_work_on() with cpu x and sytem_wq, then work will execute on cpu x. If we call queue_work() then it will queue the work on local cpu. Yeap, !WQ_UNBOUND workqueues == per-cpu workqueues. At this time local cpu may be busy or idle (Atleast according to scheduler). We don't want a idle cpu (From schedulers perspective) to be used for running this work's handler due to two reasons. - idle cpu may be in WFI or deeper idle states and so we can avoid waking it up. I have no idea what WFI is but the physical CPU is already awake at that time. It can't be idle - it's running queue_work(). It could be running in lower freq tho, which each code piece doesn't really have much control over. - We will make idle cpu look busy and so other kernel stuff may be scheduled on it now. But we could have kept it idle for a long time. Hmmm... yeah, about the same thing I wrote, it's not really about not waking up the CPU right now physically but avoiding forcing the scheduler scheduling a pinned task on an otherwise quiescent CPU. This effectively allows the scheduler to migrate such work items towards a CPU which the scheduler considers to be better (in power or whatever) leading to noticeable powersave. And what timer are you talking about? I am not talking about deffered work only, but normal work too. Deferred work item == timer + work item. I might have wrongly phrased some part of my patch (maybe used workqueue instead of work), will fix that up. I think it'd be necessary to distinguish the physical CPU being idle and the scheduler considers it to be idle (no task to schedule on it) and explain how increasing the latter can lead to powersave. As it's currently written, it seemingly, to me anyway, suggests that the proposed change somehow avoids waking up actually idle CPU, which isn't the case as queue_work() *always* schedules on the local CPU. The local CPU can't be idle by definition. Thanks. -- tejun -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH V5 1/5] workqueues: Introduce new flag WQ_POWER_EFFICIENT for power oriented workqueues
On 29 April 2013 21:49, Tejun Heo t...@kernel.org wrote: On Mon, Apr 29, 2013 at 12:06:28PM +0530, Viresh Kumar wrote: Yeap, !WQ_UNBOUND workqueues == per-cpu workqueues. Sigh!! You were talking about thread per cpu here... Sorry for missing it earlier :( At this time local cpu may be busy or idle (Atleast according to scheduler). We don't want a idle cpu (From schedulers perspective) to be used for running this work's handler due to two reasons. - idle cpu may be in WFI or deeper idle states and so we can avoid waking it up. I have no idea what WFI is but the physical CPU is already awake at that time. It can't be idle - it's running queue_work(). It could be running in lower freq tho, which each code piece doesn't really have much control over. Stupid point. WFI: Wait for interrupt (low power mode of cpu). - We will make idle cpu look busy and so other kernel stuff may be scheduled on it now. But we could have kept it idle for a long time. Hmmm... yeah, about the same thing I wrote, it's not really about not waking up the CPU right now physically but avoiding forcing the scheduler scheduling a pinned task on an otherwise quiescent CPU. This effectively allows the scheduler to migrate such work items towards a CPU which the scheduler considers to be better (in power or whatever) leading to noticeable powersave. Correct. And what timer are you talking about? I am not talking about deffered work only, but normal work too. Deferred work item == timer + work item. Ya, i knew that :) I might have wrongly phrased some part of my patch (maybe used workqueue instead of work), will fix that up. I think it'd be necessary to distinguish the physical CPU being idle and the scheduler considers it to be idle (no task to schedule on it) and explain how increasing the latter can lead to powersave. As it's currently written, it seemingly, to me anyway, suggests that the proposed change somehow avoids waking up actually idle CPU, which isn't the case as queue_work() *always* schedules on the local CPU. The local CPU can't be idle by definition. Yes you are correct. I will fix it. -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH V5 1/5] workqueues: Introduce new flag WQ_POWER_EFFICIENT for power oriented workqueues
Hey, Viresh. It's already too late for the upcoming merge window, but things generally look good to me and I'll apply the patchset once wq/for-3.11 opens. One nitpick tho. On Thu, Apr 25, 2013 at 09:13:44AM +0530, Viresh Kumar wrote: > + workqueue.power_efficient > + Workqueues can be performance or power-oriented. > + Currently, most workqueues are bound to the CPU they per-cpu would be better > + were created on. This gives good performance (due to > + cache effects) at the cost of potentially waking up > + otherwise idle cores just to process some work. To save > + power, we can allow the work to be rescheduled on a core > + that is already awake. The above description is confusing to me. As have been discussed multiple times before, per-cpu workqueue in itself doesn't wake up the CPU physically. The timer may but per-cpu workqueue doesn't. It was confusing when this patchset was first posted and the above phrasing is still confusing. What the patchset tries to do is preventing the scheduler from perceiving the CPU as active due to the activated worker thread pinned to that CPU, right? The knob doesn't really do anything about waking up the processor in itself. It just avoids feeding the scheduler with noisy activation events and allows it to allocate work item execution according to the scheduler's view of CPU active/idleness. As the scheduler has longer / larger scope of overall CPU activities and means to regulate them, this leads to more power-efficient allocation of work item executions, right? It'd be really great if the descriptions and the comment above the flag makes this abundantly clear because it's not something too apparent. Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH V5 1/5] workqueues: Introduce new flag WQ_POWER_EFFICIENT for power oriented workqueues
Hey, Viresh. It's already too late for the upcoming merge window, but things generally look good to me and I'll apply the patchset once wq/for-3.11 opens. One nitpick tho. On Thu, Apr 25, 2013 at 09:13:44AM +0530, Viresh Kumar wrote: + workqueue.power_efficient + Workqueues can be performance or power-oriented. + Currently, most workqueues are bound to the CPU they per-cpu would be better + were created on. This gives good performance (due to + cache effects) at the cost of potentially waking up + otherwise idle cores just to process some work. To save + power, we can allow the work to be rescheduled on a core + that is already awake. The above description is confusing to me. As have been discussed multiple times before, per-cpu workqueue in itself doesn't wake up the CPU physically. The timer may but per-cpu workqueue doesn't. It was confusing when this patchset was first posted and the above phrasing is still confusing. What the patchset tries to do is preventing the scheduler from perceiving the CPU as active due to the activated worker thread pinned to that CPU, right? The knob doesn't really do anything about waking up the processor in itself. It just avoids feeding the scheduler with noisy activation events and allows it to allocate work item execution according to the scheduler's view of CPU active/idleness. As the scheduler has longer / larger scope of overall CPU activities and means to regulate them, this leads to more power-efficient allocation of work item executions, right? It'd be really great if the descriptions and the comment above the flag makes this abundantly clear because it's not something too apparent. Thanks. -- tejun -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH V5 1/5] workqueues: Introduce new flag WQ_POWER_EFFICIENT for power oriented workqueues
On 25 April 2013 16:43, Amit Kucheria wrote: > On Thu, Apr 25, 2013 at 9:13 AM, Viresh Kumar wrote: >> On 25 April 2013 09:00, Amit Kucheria wrote: >>> Yes. That was my intention - preventing a prompt on existing defconfigs and >>> there by maintaining current behavior. >> >> Hmm... Following is the version after fixing all problems you reported. >> @Tejun: I have attached it too as gmail's copy-paste may break it. Please >> consider applying this series if it looks fine to you. >> >> >> ---xx- >> >> From: Viresh Kumar >> Date: Mon, 8 Apr 2013 16:45:40 +0530 >> Subject: [PATCH V5 1/5] workqueues: Introduce new flag WQ_POWER_EFFICIENT for >> power oriented workqueues >> >> Workqueues can be performance or power-oriented. Currently, most workqueues >> are >> bound to the CPU they were created on. This gives good performance (due to >> cache >> effects) at the cost of potentially waking up otherwise idle cores just to >> process some work. To save power, we can allow the work to be rescheduled on >> a >> core that is already awake. >> >> Workqueues created with the WQ_UNBOUND flag will allow some power savings. >> However, we don't change the default behaviour of the system. To enable >> power-saving behaviour, a new config option CONFIG_WQ_POWER_EFFICIENT needs >> to >> be turned on. This option can also be overridden by the >> workqueue.power_efficient boot parameter. >> >> Signed-off-by: Viresh Kumar > > For the series, you can add my: > > Reviewed-by: Amit Kucheria Thanks. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH V5 1/5] workqueues: Introduce new flag WQ_POWER_EFFICIENT for power oriented workqueues
On Thu, Apr 25, 2013 at 9:13 AM, Viresh Kumar wrote:
> On 25 April 2013 09:00, Amit Kucheria wrote:
>> Yes. That was my intention - preventing a prompt on existing defconfigs and
>> there by maintaining current behavior.
>
> Hmm... Following is the version after fixing all problems you reported.
> @Tejun: I have attached it too as gmail's copy-paste may break it. Please
> consider applying this series if it looks fine to you.
>
>
> ---xx-
>
> From: Viresh Kumar
> Date: Mon, 8 Apr 2013 16:45:40 +0530
> Subject: [PATCH V5 1/5] workqueues: Introduce new flag WQ_POWER_EFFICIENT for
> power oriented workqueues
>
> Workqueues can be performance or power-oriented. Currently, most workqueues
> are
> bound to the CPU they were created on. This gives good performance (due to
> cache
> effects) at the cost of potentially waking up otherwise idle cores just to
> process some work. To save power, we can allow the work to be rescheduled on a
> core that is already awake.
>
> Workqueues created with the WQ_UNBOUND flag will allow some power savings.
> However, we don't change the default behaviour of the system. To enable
> power-saving behaviour, a new config option CONFIG_WQ_POWER_EFFICIENT needs to
> be turned on. This option can also be overridden by the
> workqueue.power_efficient boot parameter.
>
> Signed-off-by: Viresh Kumar
For the series, you can add my:
Reviewed-by: Amit Kucheria
> ---
> Documentation/kernel-parameters.txt | 17 +
> include/linux/workqueue.h | 3 +++
> kernel/power/Kconfig| 19 +++
> kernel/workqueue.c | 11 +++
> 4 files changed, 50 insertions(+)
>
> diff --git a/Documentation/kernel-parameters.txt
> b/Documentation/kernel-parameters.txt
> index c4fa000..22edc83 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -3312,6 +3312,23 @@ bytes respectively. Such letter suffixes can
> also be entirely omitted.
> that this also can be controlled per-workqueue for
> workqueues visible under /sys/bus/workqueue/.
>
> + workqueue.power_efficient
> + Workqueues can be performance or power-oriented.
> + Currently, most workqueues are bound to the CPU they
> + were created on. This gives good performance (due to
> + cache effects) at the cost of potentially waking up
> + otherwise idle cores just to process some work. To
> save
> + power, we can allow the work to be rescheduled on a
> core
> + that is already awake.
> +
> + Workqueues created with the WQ_UNBOUND flag will allow
> + some power savings. However, we don't change the
> + default behaviour of the system. To enable
> power-saving
> + behaviour, a new config option
> CONFIG_WQ_POWER_EFFICIENT
> + needs to be turned on. This option can also be
> + overridden by the workqueue.power_efficient boot
> + parameter.
> +
> x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
> default x2apic cluster mode on platforms
> supporting x2apic.
> diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
> index 623488f..83fa570 100644
> --- a/include/linux/workqueue.h
> +++ b/include/linux/workqueue.h
> @@ -302,6 +302,9 @@ enum {
> WQ_HIGHPRI = 1 << 4, /* high priority */
> WQ_CPU_INTENSIVE= 1 << 5, /* cpu instensive workqueue */
> WQ_SYSFS= 1 << 6, /* visible in sysfs, see
> wq_sysfs_register() */
> + WQ_POWER_EFFICIENT = 1 << 7, /* WQ_UNBOUND, for power
> + * saving, if wq_power_efficient is
> + * enabled. Unused otherwise. */
>
> __WQ_DRAINING = 1 << 16, /* internal: workqueue is draining
> */
> __WQ_ORDERED= 1 << 17, /* internal: workqueue is ordered
> */
> diff --git a/kernel/power/Kconfig b/kernel/power/Kconfig
> index 5dfdc9e..018f039 100644
> --- a/kernel/power/Kconfig
> +++ b/kernel/power/Kconfig
> @@ -263,6 +263,25 @@ config PM_GENERIC_DOMAINS
> bool
> depends on PM
>
> +config WQ_POWER_EFFICIENT
> + bool "Workqueue allocated as UNBOUND (by default) for power
> efficiency"
> + depends on PM
> + default n
> + help
> + Workqueues can be performance or power-oriented. Currently, most
> + workqueues are bound to the CPU they were created on. This gives
> good
> + performance (due to cache effects) at the cost of potentially waking
> + up otherwise idle cores just
Re: [PATCH V5 1/5] workqueues: Introduce new flag WQ_POWER_EFFICIENT for power oriented workqueues
On Thu, Apr 25, 2013 at 9:13 AM, Viresh Kumar viresh.ku...@linaro.org wrote:
On 25 April 2013 09:00, Amit Kucheria amit.kuche...@linaro.org wrote:
Yes. That was my intention - preventing a prompt on existing defconfigs and
there by maintaining current behavior.
Hmm... Following is the version after fixing all problems you reported.
@Tejun: I have attached it too as gmail's copy-paste may break it. Please
consider applying this series if it looks fine to you.
---xx-
From: Viresh Kumar viresh.ku...@linaro.org
Date: Mon, 8 Apr 2013 16:45:40 +0530
Subject: [PATCH V5 1/5] workqueues: Introduce new flag WQ_POWER_EFFICIENT for
power oriented workqueues
Workqueues can be performance or power-oriented. Currently, most workqueues
are
bound to the CPU they were created on. This gives good performance (due to
cache
effects) at the cost of potentially waking up otherwise idle cores just to
process some work. To save power, we can allow the work to be rescheduled on a
core that is already awake.
Workqueues created with the WQ_UNBOUND flag will allow some power savings.
However, we don't change the default behaviour of the system. To enable
power-saving behaviour, a new config option CONFIG_WQ_POWER_EFFICIENT needs to
be turned on. This option can also be overridden by the
workqueue.power_efficient boot parameter.
Signed-off-by: Viresh Kumar viresh.ku...@linaro.org
For the series, you can add my:
Reviewed-by: Amit Kucheria amit.kuche...@linaro.org
---
Documentation/kernel-parameters.txt | 17 +
include/linux/workqueue.h | 3 +++
kernel/power/Kconfig| 19 +++
kernel/workqueue.c | 11 +++
4 files changed, 50 insertions(+)
diff --git a/Documentation/kernel-parameters.txt
b/Documentation/kernel-parameters.txt
index c4fa000..22edc83 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -3312,6 +3312,23 @@ bytes respectively. Such letter suffixes can
also be entirely omitted.
that this also can be controlled per-workqueue for
workqueues visible under /sys/bus/workqueue/.
+ workqueue.power_efficient
+ Workqueues can be performance or power-oriented.
+ Currently, most workqueues are bound to the CPU they
+ were created on. This gives good performance (due to
+ cache effects) at the cost of potentially waking up
+ otherwise idle cores just to process some work. To
save
+ power, we can allow the work to be rescheduled on a
core
+ that is already awake.
+
+ Workqueues created with the WQ_UNBOUND flag will allow
+ some power savings. However, we don't change the
+ default behaviour of the system. To enable
power-saving
+ behaviour, a new config option
CONFIG_WQ_POWER_EFFICIENT
+ needs to be turned on. This option can also be
+ overridden by the workqueue.power_efficient boot
+ parameter.
+
x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
default x2apic cluster mode on platforms
supporting x2apic.
diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index 623488f..83fa570 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -302,6 +302,9 @@ enum {
WQ_HIGHPRI = 1 4, /* high priority */
WQ_CPU_INTENSIVE= 1 5, /* cpu instensive workqueue */
WQ_SYSFS= 1 6, /* visible in sysfs, see
wq_sysfs_register() */
+ WQ_POWER_EFFICIENT = 1 7, /* WQ_UNBOUND, for power
+ * saving, if wq_power_efficient is
+ * enabled. Unused otherwise. */
__WQ_DRAINING = 1 16, /* internal: workqueue is draining
*/
__WQ_ORDERED= 1 17, /* internal: workqueue is ordered
*/
diff --git a/kernel/power/Kconfig b/kernel/power/Kconfig
index 5dfdc9e..018f039 100644
--- a/kernel/power/Kconfig
+++ b/kernel/power/Kconfig
@@ -263,6 +263,25 @@ config PM_GENERIC_DOMAINS
bool
depends on PM
+config WQ_POWER_EFFICIENT
+ bool Workqueue allocated as UNBOUND (by default) for power
efficiency
+ depends on PM
+ default n
+ help
+ Workqueues can be performance or power-oriented. Currently, most
+ workqueues are bound to the CPU they were created on. This gives
good
+ performance (due to cache effects) at the cost of potentially waking
+ up otherwise idle cores just to
Re: [PATCH V5 1/5] workqueues: Introduce new flag WQ_POWER_EFFICIENT for power oriented workqueues
On 25 April 2013 16:43, Amit Kucheria amit.kuche...@linaro.org wrote: On Thu, Apr 25, 2013 at 9:13 AM, Viresh Kumar viresh.ku...@linaro.org wrote: On 25 April 2013 09:00, Amit Kucheria amit.kuche...@linaro.org wrote: Yes. That was my intention - preventing a prompt on existing defconfigs and there by maintaining current behavior. Hmm... Following is the version after fixing all problems you reported. @Tejun: I have attached it too as gmail's copy-paste may break it. Please consider applying this series if it looks fine to you. ---xx- From: Viresh Kumar viresh.ku...@linaro.org Date: Mon, 8 Apr 2013 16:45:40 +0530 Subject: [PATCH V5 1/5] workqueues: Introduce new flag WQ_POWER_EFFICIENT for power oriented workqueues Workqueues can be performance or power-oriented. Currently, most workqueues are bound to the CPU they were created on. This gives good performance (due to cache effects) at the cost of potentially waking up otherwise idle cores just to process some work. To save power, we can allow the work to be rescheduled on a core that is already awake. Workqueues created with the WQ_UNBOUND flag will allow some power savings. However, we don't change the default behaviour of the system. To enable power-saving behaviour, a new config option CONFIG_WQ_POWER_EFFICIENT needs to be turned on. This option can also be overridden by the workqueue.power_efficient boot parameter. Signed-off-by: Viresh Kumar viresh.ku...@linaro.org For the series, you can add my: Reviewed-by: Amit Kucheria amit.kuche...@linaro.org Thanks. -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH V5 1/5] workqueues: Introduce new flag WQ_POWER_EFFICIENT for power oriented workqueues
On 25 April 2013 09:00, Amit Kucheria wrote:
> Yes. That was my intention - preventing a prompt on existing defconfigs and
> there by maintaining current behavior.
Hmm... Following is the version after fixing all problems you reported.
@Tejun: I have attached it too as gmail's copy-paste may break it. Please
consider applying this series if it looks fine to you.
---xx-
From: Viresh Kumar
Date: Mon, 8 Apr 2013 16:45:40 +0530
Subject: [PATCH V5 1/5] workqueues: Introduce new flag WQ_POWER_EFFICIENT for
power oriented workqueues
Workqueues can be performance or power-oriented. Currently, most workqueues are
bound to the CPU they were created on. This gives good performance (due to cache
effects) at the cost of potentially waking up otherwise idle cores just to
process some work. To save power, we can allow the work to be rescheduled on a
core that is already awake.
Workqueues created with the WQ_UNBOUND flag will allow some power savings.
However, we don't change the default behaviour of the system. To enable
power-saving behaviour, a new config option CONFIG_WQ_POWER_EFFICIENT needs to
be turned on. This option can also be overridden by the
workqueue.power_efficient boot parameter.
Signed-off-by: Viresh Kumar
---
Documentation/kernel-parameters.txt | 17 +
include/linux/workqueue.h | 3 +++
kernel/power/Kconfig| 19 +++
kernel/workqueue.c | 11 +++
4 files changed, 50 insertions(+)
diff --git a/Documentation/kernel-parameters.txt
b/Documentation/kernel-parameters.txt
index c4fa000..22edc83 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -3312,6 +3312,23 @@ bytes respectively. Such letter suffixes can
also be entirely omitted.
that this also can be controlled per-workqueue for
workqueues visible under /sys/bus/workqueue/.
+ workqueue.power_efficient
+ Workqueues can be performance or power-oriented.
+ Currently, most workqueues are bound to the CPU they
+ were created on. This gives good performance (due to
+ cache effects) at the cost of potentially waking up
+ otherwise idle cores just to process some work. To save
+ power, we can allow the work to be rescheduled on a core
+ that is already awake.
+
+ Workqueues created with the WQ_UNBOUND flag will allow
+ some power savings. However, we don't change the
+ default behaviour of the system. To enable power-saving
+ behaviour, a new config option CONFIG_WQ_POWER_EFFICIENT
+ needs to be turned on. This option can also be
+ overridden by the workqueue.power_efficient boot
+ parameter.
+
x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
default x2apic cluster mode on platforms
supporting x2apic.
diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index 623488f..83fa570 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -302,6 +302,9 @@ enum {
WQ_HIGHPRI = 1 << 4, /* high priority */
WQ_CPU_INTENSIVE= 1 << 5, /* cpu instensive workqueue */
WQ_SYSFS= 1 << 6, /* visible in sysfs, see
wq_sysfs_register() */
+ WQ_POWER_EFFICIENT = 1 << 7, /* WQ_UNBOUND, for power
+ * saving, if wq_power_efficient is
+ * enabled. Unused otherwise. */
__WQ_DRAINING = 1 << 16, /* internal: workqueue is draining */
__WQ_ORDERED= 1 << 17, /* internal: workqueue is ordered */
diff --git a/kernel/power/Kconfig b/kernel/power/Kconfig
index 5dfdc9e..018f039 100644
--- a/kernel/power/Kconfig
+++ b/kernel/power/Kconfig
@@ -263,6 +263,25 @@ config PM_GENERIC_DOMAINS
bool
depends on PM
+config WQ_POWER_EFFICIENT
+ bool "Workqueue allocated as UNBOUND (by default) for power efficiency"
+ depends on PM
+ default n
+ help
+ Workqueues can be performance or power-oriented. Currently, most
+ workqueues are bound to the CPU they were created on. This gives good
+ performance (due to cache effects) at the cost of potentially waking
+ up otherwise idle cores just to process some work. To save power, we
+ can allow the work to be rescheduled on a core that is already awake.
+
+ Workqueues created with the WQ_UNBOUND flag will allow some power
+ savings. However, we don't change the default behaviour of the
+ system. To enable power-saving behaviour, a new
Re: [PATCH V5 1/5] workqueues: Introduce new flag WQ_POWER_EFFICIENT for power oriented workqueues
On Wed, Apr 24, 2013 at 05:57:09PM +0530, Viresh Kumar wrote: > If this line is not present i believe it is 'default n' only. So, i skipped > it. I think the difference is that when you configure the option for the first time - ie. building kernel with .config used for an older kernel - that it prompts for selection, thus annoying the big penguin. You probably want the explicit 'N'. Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH V5 1/5] workqueues: Introduce new flag WQ_POWER_EFFICIENT for power oriented workqueues
On 24 April 2013 17:50, Amit Kucheria wrote: > On Wed, Apr 24, 2013 at 5:12 PM, Viresh Kumar wrote: >> +config WQ_POWER_EFFICIENT >> + bool "Workqueue allocated as UNBOUND (by default) for power >> efficiency" >> + depends on PM > > default n If this line is not present i believe it is 'default n' only. So, i skipped it. All others comments accepted. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH V5 1/5] workqueues: Introduce new flag WQ_POWER_EFFICIENT for power oriented workqueues
On Wed, Apr 24, 2013 at 5:12 PM, Viresh Kumar wrote:
> Workqueues can be performance or power oriented. For performance we may want
> to
> keep them running on a single cpu, so that it remains cache hot. For power we
> can give scheduler the liberty to choose target cpu for running work handler.
Consider the following rewording:
Workqueues can be performance or power-oriented. Currently, most
workqueues are bound to the CPU they were created on. This gives good
performance (due to cache effects) at the cost of potentially waking
up otherwise idle cores just to process some work. To save power, we
can allow the work to be rescheduled on a core that is already awake.
> Later one (Power oriented WQ) can be achieved if the workqueue is allocated
> with
> WQ_UNBOUND flag. Enabling CONFIG_WQ_POWER_EFFICIENT will set
> 'wq_power_efficient' to 'true'. Setting 'power_efficient' boot param will
> override value of 'wq_power_efficient' variable. When 'wq_power_efficient' is
> set to 'true', we will convert WQ_POWER_EFFICIENT flag to WQ_UNBOUND on wq
> allocation. And so scheduler will have the liberty to choose where to run this
> work.
Consider the following rewording which is easier to understand IMO:
Workqueues created with the WQ_UNBOUND flag will allow some power
savings. However, we don't change the default behaviour of the system.
To enable power-saving behaviour, a new config option
CONFIG_WQ_POWER_EFFICIENT needs to be turned on. This option can also
be overridden by the workqueue.power_efficient boot parameter.
> Signed-off-by: Viresh Kumar
> ---
> Documentation/kernel-parameters.txt | 17 +
> include/linux/workqueue.h | 3 +++
> kernel/power/Kconfig| 19 +++
> kernel/workqueue.c | 11 +++
> 4 files changed, 50 insertions(+)
>
> diff --git a/Documentation/kernel-parameters.txt
> b/Documentation/kernel-parameters.txt
> index c4fa000..a9040fa 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -3312,6 +3312,23 @@ bytes respectively. Such letter suffixes can also be
> entirely omitted.
> that this also can be controlled per-workqueue for
> workqueues visible under /sys/bus/workqueue/.
>
> + workqueue.power_efficient
> + Workqueues can be performance or power oriented. For
> + performance we may want to keep them running on a
> single
> + cpu, so that it remains cache hot. For power we can
> give
> + scheduler the liberty to choose target cpu for running
> + work handler.
> +
> + Later one (Power oriented WQ) can be achieved if the
> + workqueue is allocated with WQ_UNBOUND flag. Enabling
> + CONFIG_WQ_POWER_EFFICIENT will set
> 'wq_power_efficient'
> + to 'true'. Setting 'power_efficient' boot param will
> + override value of 'wq_power_efficient' variable. When
> + 'wq_power_efficient' is set to 'true', we will convert
> + WQ_POWER_EFFICIENT flag to WQ_UNBOUND on wq
> allocation.
> + And so scheduler will have the liberty to choose where
> + to run this work.
> +
Rewrite as above.
> x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
> default x2apic cluster mode on platforms
> supporting x2apic.
> diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
> index 623488f..83fa570 100644
> --- a/include/linux/workqueue.h
> +++ b/include/linux/workqueue.h
> @@ -302,6 +302,9 @@ enum {
> WQ_HIGHPRI = 1 << 4, /* high priority */
> WQ_CPU_INTENSIVE= 1 << 5, /* cpu instensive workqueue */
> WQ_SYSFS= 1 << 6, /* visible in sysfs, see
> wq_sysfs_register() */
> + WQ_POWER_EFFICIENT = 1 << 7, /* WQ_UNBOUND, for power
> + * saving, if wq_power_efficient is
> + * enabled. Unused otherwise. */
>
> __WQ_DRAINING = 1 << 16, /* internal: workqueue is draining
> */
> __WQ_ORDERED= 1 << 17, /* internal: workqueue is ordered
> */
> diff --git a/kernel/power/Kconfig b/kernel/power/Kconfig
> index 5dfdc9e..e1e9c8b 100644
> --- a/kernel/power/Kconfig
> +++ b/kernel/power/Kconfig
> @@ -263,6 +263,25 @@ config PM_GENERIC_DOMAINS
> bool
> depends on PM
>
> +config WQ_POWER_EFFICIENT
> + bool "Workqueue allocated as UNBOUND (by default) for power
> efficiency"
> + depends on PM
default n
> + help
> + Workqueues can be performance or power oriented. For performance we
> + may want to keep them running on a
Re: [PATCH V5 1/5] workqueues: Introduce new flag WQ_POWER_EFFICIENT for power oriented workqueues
On Wed, Apr 24, 2013 at 5:12 PM, Viresh Kumar viresh.ku...@linaro.org wrote:
Workqueues can be performance or power oriented. For performance we may want
to
keep them running on a single cpu, so that it remains cache hot. For power we
can give scheduler the liberty to choose target cpu for running work handler.
Consider the following rewording:
Workqueues can be performance or power-oriented. Currently, most
workqueues are bound to the CPU they were created on. This gives good
performance (due to cache effects) at the cost of potentially waking
up otherwise idle cores just to process some work. To save power, we
can allow the work to be rescheduled on a core that is already awake.
Later one (Power oriented WQ) can be achieved if the workqueue is allocated
with
WQ_UNBOUND flag. Enabling CONFIG_WQ_POWER_EFFICIENT will set
'wq_power_efficient' to 'true'. Setting 'power_efficient' boot param will
override value of 'wq_power_efficient' variable. When 'wq_power_efficient' is
set to 'true', we will convert WQ_POWER_EFFICIENT flag to WQ_UNBOUND on wq
allocation. And so scheduler will have the liberty to choose where to run this
work.
Consider the following rewording which is easier to understand IMO:
Workqueues created with the WQ_UNBOUND flag will allow some power
savings. However, we don't change the default behaviour of the system.
To enable power-saving behaviour, a new config option
CONFIG_WQ_POWER_EFFICIENT needs to be turned on. This option can also
be overridden by the workqueue.power_efficient boot parameter.
Signed-off-by: Viresh Kumar viresh.ku...@linaro.org
---
Documentation/kernel-parameters.txt | 17 +
include/linux/workqueue.h | 3 +++
kernel/power/Kconfig| 19 +++
kernel/workqueue.c | 11 +++
4 files changed, 50 insertions(+)
diff --git a/Documentation/kernel-parameters.txt
b/Documentation/kernel-parameters.txt
index c4fa000..a9040fa 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -3312,6 +3312,23 @@ bytes respectively. Such letter suffixes can also be
entirely omitted.
that this also can be controlled per-workqueue for
workqueues visible under /sys/bus/workqueue/.
+ workqueue.power_efficient
+ Workqueues can be performance or power oriented. For
+ performance we may want to keep them running on a
single
+ cpu, so that it remains cache hot. For power we can
give
+ scheduler the liberty to choose target cpu for running
+ work handler.
+
+ Later one (Power oriented WQ) can be achieved if the
+ workqueue is allocated with WQ_UNBOUND flag. Enabling
+ CONFIG_WQ_POWER_EFFICIENT will set
'wq_power_efficient'
+ to 'true'. Setting 'power_efficient' boot param will
+ override value of 'wq_power_efficient' variable. When
+ 'wq_power_efficient' is set to 'true', we will convert
+ WQ_POWER_EFFICIENT flag to WQ_UNBOUND on wq
allocation.
+ And so scheduler will have the liberty to choose where
+ to run this work.
+
Rewrite as above.
x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
default x2apic cluster mode on platforms
supporting x2apic.
diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index 623488f..83fa570 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -302,6 +302,9 @@ enum {
WQ_HIGHPRI = 1 4, /* high priority */
WQ_CPU_INTENSIVE= 1 5, /* cpu instensive workqueue */
WQ_SYSFS= 1 6, /* visible in sysfs, see
wq_sysfs_register() */
+ WQ_POWER_EFFICIENT = 1 7, /* WQ_UNBOUND, for power
+ * saving, if wq_power_efficient is
+ * enabled. Unused otherwise. */
__WQ_DRAINING = 1 16, /* internal: workqueue is draining
*/
__WQ_ORDERED= 1 17, /* internal: workqueue is ordered
*/
diff --git a/kernel/power/Kconfig b/kernel/power/Kconfig
index 5dfdc9e..e1e9c8b 100644
--- a/kernel/power/Kconfig
+++ b/kernel/power/Kconfig
@@ -263,6 +263,25 @@ config PM_GENERIC_DOMAINS
bool
depends on PM
+config WQ_POWER_EFFICIENT
+ bool Workqueue allocated as UNBOUND (by default) for power
efficiency
+ depends on PM
default n
+ help
+ Workqueues can be performance or power oriented. For performance we
+ may want to keep them running on a single cpu, so that it remains
+ cache hot. For
Re: [PATCH V5 1/5] workqueues: Introduce new flag WQ_POWER_EFFICIENT for power oriented workqueues
On 24 April 2013 17:50, Amit Kucheria amit.kuche...@linaro.org wrote: On Wed, Apr 24, 2013 at 5:12 PM, Viresh Kumar viresh.ku...@linaro.org wrote: +config WQ_POWER_EFFICIENT + bool Workqueue allocated as UNBOUND (by default) for power efficiency + depends on PM default n If this line is not present i believe it is 'default n' only. So, i skipped it. All others comments accepted. -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH V5 1/5] workqueues: Introduce new flag WQ_POWER_EFFICIENT for power oriented workqueues
On Wed, Apr 24, 2013 at 05:57:09PM +0530, Viresh Kumar wrote: If this line is not present i believe it is 'default n' only. So, i skipped it. I think the difference is that when you configure the option for the first time - ie. building kernel with .config used for an older kernel - that it prompts for selection, thus annoying the big penguin. You probably want the explicit 'N'. Thanks. -- tejun -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH V5 1/5] workqueues: Introduce new flag WQ_POWER_EFFICIENT for power oriented workqueues
On 25 April 2013 09:00, Amit Kucheria amit.kuche...@linaro.org wrote:
Yes. That was my intention - preventing a prompt on existing defconfigs and
there by maintaining current behavior.
Hmm... Following is the version after fixing all problems you reported.
@Tejun: I have attached it too as gmail's copy-paste may break it. Please
consider applying this series if it looks fine to you.
---xx-
From: Viresh Kumar viresh.ku...@linaro.org
Date: Mon, 8 Apr 2013 16:45:40 +0530
Subject: [PATCH V5 1/5] workqueues: Introduce new flag WQ_POWER_EFFICIENT for
power oriented workqueues
Workqueues can be performance or power-oriented. Currently, most workqueues are
bound to the CPU they were created on. This gives good performance (due to cache
effects) at the cost of potentially waking up otherwise idle cores just to
process some work. To save power, we can allow the work to be rescheduled on a
core that is already awake.
Workqueues created with the WQ_UNBOUND flag will allow some power savings.
However, we don't change the default behaviour of the system. To enable
power-saving behaviour, a new config option CONFIG_WQ_POWER_EFFICIENT needs to
be turned on. This option can also be overridden by the
workqueue.power_efficient boot parameter.
Signed-off-by: Viresh Kumar viresh.ku...@linaro.org
---
Documentation/kernel-parameters.txt | 17 +
include/linux/workqueue.h | 3 +++
kernel/power/Kconfig| 19 +++
kernel/workqueue.c | 11 +++
4 files changed, 50 insertions(+)
diff --git a/Documentation/kernel-parameters.txt
b/Documentation/kernel-parameters.txt
index c4fa000..22edc83 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -3312,6 +3312,23 @@ bytes respectively. Such letter suffixes can
also be entirely omitted.
that this also can be controlled per-workqueue for
workqueues visible under /sys/bus/workqueue/.
+ workqueue.power_efficient
+ Workqueues can be performance or power-oriented.
+ Currently, most workqueues are bound to the CPU they
+ were created on. This gives good performance (due to
+ cache effects) at the cost of potentially waking up
+ otherwise idle cores just to process some work. To save
+ power, we can allow the work to be rescheduled on a core
+ that is already awake.
+
+ Workqueues created with the WQ_UNBOUND flag will allow
+ some power savings. However, we don't change the
+ default behaviour of the system. To enable power-saving
+ behaviour, a new config option CONFIG_WQ_POWER_EFFICIENT
+ needs to be turned on. This option can also be
+ overridden by the workqueue.power_efficient boot
+ parameter.
+
x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
default x2apic cluster mode on platforms
supporting x2apic.
diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index 623488f..83fa570 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -302,6 +302,9 @@ enum {
WQ_HIGHPRI = 1 4, /* high priority */
WQ_CPU_INTENSIVE= 1 5, /* cpu instensive workqueue */
WQ_SYSFS= 1 6, /* visible in sysfs, see
wq_sysfs_register() */
+ WQ_POWER_EFFICIENT = 1 7, /* WQ_UNBOUND, for power
+ * saving, if wq_power_efficient is
+ * enabled. Unused otherwise. */
__WQ_DRAINING = 1 16, /* internal: workqueue is draining */
__WQ_ORDERED= 1 17, /* internal: workqueue is ordered */
diff --git a/kernel/power/Kconfig b/kernel/power/Kconfig
index 5dfdc9e..018f039 100644
--- a/kernel/power/Kconfig
+++ b/kernel/power/Kconfig
@@ -263,6 +263,25 @@ config PM_GENERIC_DOMAINS
bool
depends on PM
+config WQ_POWER_EFFICIENT
+ bool Workqueue allocated as UNBOUND (by default) for power efficiency
+ depends on PM
+ default n
+ help
+ Workqueues can be performance or power-oriented. Currently, most
+ workqueues are bound to the CPU they were created on. This gives good
+ performance (due to cache effects) at the cost of potentially waking
+ up otherwise idle cores just to process some work. To save power, we
+ can allow the work to be rescheduled on a core that is already awake.
+
+ Workqueues created with the WQ_UNBOUND flag will allow some power
+ savings. However, we don't change the default behaviour of the
+
