RE: [PATCH V2] watchdog: optimizing the hrtimer interval for power saving
> It seems like a better approach would be to adjust the timer somehow when > you change c-states. The whole point of the hard and softlockup is to > detect if scheduled code is either deadlock or hogging the cpu for too long. > > If the cpu is in a deep sleep, then nothing is running, right? Which > means nothing can deadlock or hog the cpu. In those cases you can > probably temporarily disable the lockup detector until the cpu wakes up > from that c-state and starts scheduling code again. > You are right, I ever tried the thought, when CPU is idle, we can pause the hrtimer, After wakeup, we resume the hrtimer again. But I found sometimes the in idle and out of idle is too frequent. Anyway, you advice seems the right way, I will try to dig something more deeply. Thanks. > In that case you can really maximize your power savings (and probably get > powerTop to stop telling everyone to disable the nmi_watchdog :-) ). > > Ideally in a deep sleep you don't want any soft interrupts running, no? > > Just a thought. > > Cheers, > Don -- 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 V2] watchdog: optimizing the hrtimer interval for power saving
On Wed, Nov 28, 2012 at 07:24:52PM +0800, Chuansheng Liu wrote: > > By default, the watchdog threshold is 10, it means every 4s > every CPU will receive one hrtimer interrupt, for low power > device, it will cause 4-5mV power impact when device is deep > sleep. > > So here want to optimize it as below: > 4s + 4s + 4s + 4s + 4s > == > > 1s + 9s + 9s ... > Or > 1s + 1s..+ 9s + 9s > > For soft lockup detection, it will have more than 5 chances to > hit, once one chance is successful, we will start 9s hrtimer > instead of 1s; > > For hard lockup dection, it will have more than 2 chances to hit, > As Don said, the min window is 10s just when CPU is always running > as MAX frequency. In most case, the window is 60s, so we should > have much more than 2 chances. > > With this patch, in most cases the hrtimer will be 9s instead > of 4s averagely. It can save the device power indeed. > > Change log: > Since V1: In V1, Don pointed out, "12 seconds will miss the window > repeatedly." So here set the long period < min window 10s. Hmm. My only concern is if you are solving this the right way. The Chrome folks wanted this threshold to be smaller like 2 seconds, which would defeat the whole point of this patch. It seems like a better approach would be to adjust the timer somehow when you change c-states. The whole point of the hard and softlockup is to detect if scheduled code is either deadlock or hogging the cpu for too long. If the cpu is in a deep sleep, then nothing is running, right? Which means nothing can deadlock or hog the cpu. In those cases you can probably temporarily disable the lockup detector until the cpu wakes up from that c-state and starts scheduling code again. In that case you can really maximize your power savings (and probably get powerTop to stop telling everyone to disable the nmi_watchdog :-) ). Ideally in a deep sleep you don't want any soft interrupts running, no? Just a thought. Cheers, Don -- 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 V2] watchdog: optimizing the hrtimer interval for power saving
On Wed, Nov 28, 2012 at 07:24:52PM +0800, Chuansheng Liu wrote: By default, the watchdog threshold is 10, it means every 4s every CPU will receive one hrtimer interrupt, for low power device, it will cause 4-5mV power impact when device is deep sleep. So here want to optimize it as below: 4s + 4s + 4s + 4s + 4s == 1s + 9s + 9s ... Or 1s + 1s..+ 9s + 9s For soft lockup detection, it will have more than 5 chances to hit, once one chance is successful, we will start 9s hrtimer instead of 1s; For hard lockup dection, it will have more than 2 chances to hit, As Don said, the min window is 10s just when CPU is always running as MAX frequency. In most case, the window is 60s, so we should have much more than 2 chances. With this patch, in most cases the hrtimer will be 9s instead of 4s averagely. It can save the device power indeed. Change log: Since V1: In V1, Don pointed out, 12 seconds will miss the window repeatedly. So here set the long period min window 10s. Hmm. My only concern is if you are solving this the right way. The Chrome folks wanted this threshold to be smaller like 2 seconds, which would defeat the whole point of this patch. It seems like a better approach would be to adjust the timer somehow when you change c-states. The whole point of the hard and softlockup is to detect if scheduled code is either deadlock or hogging the cpu for too long. If the cpu is in a deep sleep, then nothing is running, right? Which means nothing can deadlock or hog the cpu. In those cases you can probably temporarily disable the lockup detector until the cpu wakes up from that c-state and starts scheduling code again. In that case you can really maximize your power savings (and probably get powerTop to stop telling everyone to disable the nmi_watchdog :-) ). Ideally in a deep sleep you don't want any soft interrupts running, no? Just a thought. Cheers, Don -- 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 V2] watchdog: optimizing the hrtimer interval for power saving
It seems like a better approach would be to adjust the timer somehow when you change c-states. The whole point of the hard and softlockup is to detect if scheduled code is either deadlock or hogging the cpu for too long. If the cpu is in a deep sleep, then nothing is running, right? Which means nothing can deadlock or hog the cpu. In those cases you can probably temporarily disable the lockup detector until the cpu wakes up from that c-state and starts scheduling code again. You are right, I ever tried the thought, when CPU is idle, we can pause the hrtimer, After wakeup, we resume the hrtimer again. But I found sometimes the in idle and out of idle is too frequent. Anyway, you advice seems the right way, I will try to dig something more deeply. Thanks. In that case you can really maximize your power savings (and probably get powerTop to stop telling everyone to disable the nmi_watchdog :-) ). Ideally in a deep sleep you don't want any soft interrupts running, no? Just a thought. Cheers, Don -- 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/
[PATCH V2] watchdog: optimizing the hrtimer interval for power saving
By default, the watchdog threshold is 10, it means every 4s
every CPU will receive one hrtimer interrupt, for low power
device, it will cause 4-5mV power impact when device is deep
sleep.
So here want to optimize it as below:
4s + 4s + 4s + 4s + 4s
== >
1s + 9s + 9s ...
Or
1s + 1s..+ 9s + 9s
For soft lockup detection, it will have more than 5 chances to
hit, once one chance is successful, we will start 9s hrtimer
instead of 1s;
For hard lockup dection, it will have more than 2 chances to hit,
As Don said, the min window is 10s just when CPU is always running
as MAX frequency. In most case, the window is 60s, so we should
have much more than 2 chances.
With this patch, in most cases the hrtimer will be 9s instead
of 4s averagely. It can save the device power indeed.
Change log:
Since V1: In V1, Don pointed out, "12 seconds will miss the window
repeatedly." So here set the long period < min window 10s.
Signed-off-by: liu chuansheng
---
kernel/watchdog.c | 30 --
1 files changed, 28 insertions(+), 2 deletions(-)
diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index dd4b80a..b37d682 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -125,7 +125,24 @@ static u64 get_sample_period(void)
* and hard thresholds) to increment before the
* hardlockup detector generates a warning
*/
- return get_softlockup_thresh() * ((u64)NSEC_PER_SEC / 5);
+ return get_softlockup_thresh() * ((u64)NSEC_PER_SEC / 20);
+}
+
+static u64 get_long_sample_period(void)
+{
+ /*
+* convert watchdog_thresh from seconds to ns
+* We want to give 5 chances to detect softlockup,
+* for power saving, once one chance is succeeding,
+* we can set long period to avoid power consumption.
+* Currently, set the long sample period is:
+* 9s = 10s - 1s, the reason is for covering the window
+* of nmi interrupt 10s interval.
+* So at least, for hard lockup, it has >=2 chances,
+* for soft lockup, it has >= 5 chances.
+*
+*/
+ return (watchdog_thresh * (u64)NSEC_PER_SEC) - get_sample_period();
}
/* Commands for resetting the watchdog */
@@ -267,6 +284,10 @@ static enum hrtimer_restart watchdog_timer_fn(struct
hrtimer *hrtimer)
unsigned long touch_ts = __this_cpu_read(watchdog_touch_ts);
struct pt_regs *regs = get_irq_regs();
int duration;
+ bool is_touched;
+
+ is_touched = (__this_cpu_read(hrtimer_interrupts) ==
+ __this_cpu_read(soft_lockup_hrtimer_cnt));
/* kick the hardlockup detector */
watchdog_interrupt_count();
@@ -275,7 +296,12 @@ static enum hrtimer_restart watchdog_timer_fn(struct
hrtimer *hrtimer)
wake_up_process(__this_cpu_read(softlockup_watchdog));
/* .. and repeat */
- hrtimer_forward_now(hrtimer, ns_to_ktime(get_sample_period()));
+ if (is_touched) {
+ hrtimer_forward_now(hrtimer,
+ ns_to_ktime(get_long_sample_period()));
+ } else {
+ hrtimer_forward_now(hrtimer, ns_to_ktime(get_sample_period()));
+ }
if (touch_ts == 0) {
if (unlikely(__this_cpu_read(softlockup_touch_sync))) {
--
1.7.0.4
--
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Please read the FAQ at http://www.tux.org/lkml/
[PATCH V2] watchdog: optimizing the hrtimer interval for power saving
By default, the watchdog threshold is 10, it means every 4s
every CPU will receive one hrtimer interrupt, for low power
device, it will cause 4-5mV power impact when device is deep
sleep.
So here want to optimize it as below:
4s + 4s + 4s + 4s + 4s
==
1s + 9s + 9s ...
Or
1s + 1s..+ 9s + 9s
For soft lockup detection, it will have more than 5 chances to
hit, once one chance is successful, we will start 9s hrtimer
instead of 1s;
For hard lockup dection, it will have more than 2 chances to hit,
As Don said, the min window is 10s just when CPU is always running
as MAX frequency. In most case, the window is 60s, so we should
have much more than 2 chances.
With this patch, in most cases the hrtimer will be 9s instead
of 4s averagely. It can save the device power indeed.
Change log:
Since V1: In V1, Don pointed out, 12 seconds will miss the window
repeatedly. So here set the long period min window 10s.
Signed-off-by: liu chuansheng chuansheng@intel.com
---
kernel/watchdog.c | 30 --
1 files changed, 28 insertions(+), 2 deletions(-)
diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index dd4b80a..b37d682 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -125,7 +125,24 @@ static u64 get_sample_period(void)
* and hard thresholds) to increment before the
* hardlockup detector generates a warning
*/
- return get_softlockup_thresh() * ((u64)NSEC_PER_SEC / 5);
+ return get_softlockup_thresh() * ((u64)NSEC_PER_SEC / 20);
+}
+
+static u64 get_long_sample_period(void)
+{
+ /*
+* convert watchdog_thresh from seconds to ns
+* We want to give 5 chances to detect softlockup,
+* for power saving, once one chance is succeeding,
+* we can set long period to avoid power consumption.
+* Currently, set the long sample period is:
+* 9s = 10s - 1s, the reason is for covering the window
+* of nmi interrupt 10s interval.
+* So at least, for hard lockup, it has =2 chances,
+* for soft lockup, it has = 5 chances.
+*
+*/
+ return (watchdog_thresh * (u64)NSEC_PER_SEC) - get_sample_period();
}
/* Commands for resetting the watchdog */
@@ -267,6 +284,10 @@ static enum hrtimer_restart watchdog_timer_fn(struct
hrtimer *hrtimer)
unsigned long touch_ts = __this_cpu_read(watchdog_touch_ts);
struct pt_regs *regs = get_irq_regs();
int duration;
+ bool is_touched;
+
+ is_touched = (__this_cpu_read(hrtimer_interrupts) ==
+ __this_cpu_read(soft_lockup_hrtimer_cnt));
/* kick the hardlockup detector */
watchdog_interrupt_count();
@@ -275,7 +296,12 @@ static enum hrtimer_restart watchdog_timer_fn(struct
hrtimer *hrtimer)
wake_up_process(__this_cpu_read(softlockup_watchdog));
/* .. and repeat */
- hrtimer_forward_now(hrtimer, ns_to_ktime(get_sample_period()));
+ if (is_touched) {
+ hrtimer_forward_now(hrtimer,
+ ns_to_ktime(get_long_sample_period()));
+ } else {
+ hrtimer_forward_now(hrtimer, ns_to_ktime(get_sample_period()));
+ }
if (touch_ts == 0) {
if (unlikely(__this_cpu_read(softlockup_touch_sync))) {
--
1.7.0.4
--
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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/
