Re: [PATCH v8 5/8] tracepoint: Make rcuidle tracepoint callers use SRCU
- On May 31, 2018, at 1:51 PM, Joel Fernandes, Google
j...@joelfernandes.org wrote:
>> I find it odd to have a "return" in a macro that consists of a
>> do { } while (0). I'm tempted to replace "return" by "break" here,
>> to break the macro do/while (0) loop.
>
> "return;" is also used from "if (!(cond))" above so I prefer be consistent
> and just use return than break as done above, but please let me know if you
> still object.
It's fine by me,
Thanks!
Mathieu
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
Re: [PATCH v8 5/8] tracepoint: Make rcuidle tracepoint callers use SRCU
On Thu, May 31, 2018 at 02:50:41AM -0400, Mathieu Desnoyers wrote:
> - On May 30, 2018, at 2:04 AM, Joel Fernandes joe...@google.com wrote:
>
> > From: "Joel Fernandes (Google)"
> >
> > In recent tests with IRQ on/off tracepoints, a large performance
> > overhead ~10% is noticed when running hackbench. This is root caused to
> > calls to rcu_irq_enter_irqson and rcu_irq_exit_irqson from the
> > tracepoint code. Following a long discussion on the list [1] about this,
> > we concluded that srcu is a better alternative for use during rcu idle.
> > Although it does involve extra barriers, its lighter than the sched-rcu
> > version which has to do additional RCU calls to notify RCU idle about
> > entry into RCU sections.
> >
> > In this patch, we change the underlying implementation of the
> > trace_*_rcuidle API to use SRCU. This has shown to improve performance
> > alot for the high frequency irq enable/disable tracepoints.
> >
> > Test: Tested idle and preempt/irq tracepoints.
> >
> > Here are some performance numbers:
> >
> > With a run of the following 30 times on a single core x86 Qemu instance
> > with 1GB memory:
> > hackbench -g 4 -f 2 -l 3000
> >
> > Completion times in seconds. CONFIG_PROVE_LOCKING=y.
> >
> > No patches (without this series)
> > Mean: 3.048
> > Median: 3.025
> > Std Dev: 0.064
> >
> > With Lockdep using irq tracepoints with RCU implementation:
> > Mean: 3.451 (-11.66 %)
> > Median: 3.447 (-12.22%)
> > Std Dev: 0.049
> >
> > With Lockdep using irq tracepoints with SRCU implementation (this series):
> > Mean: 3.020 (I would consider the improvement against the "without
> >this series" case as just noise).
> > Median: 3.013
> > Std Dev: 0.033
> >
> > [1] https://patchwork.kernel.org/patch/10344297/
> >
> > Signed-off-by: Joel Fernandes (Google)
> > ---
> > include/linux/tracepoint.h | 48 +++---
> > kernel/tracepoint.c| 15 +++-
> > 2 files changed, 54 insertions(+), 9 deletions(-)
> >
> > diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
> > index c94f466d57ef..880794207921 100644
> > --- a/include/linux/tracepoint.h
> > +++ b/include/linux/tracepoint.h
> > @@ -15,6 +15,7 @@
> > */
> >
> > #include
> > +#include
> > #include
> > #include
> > #include
> > @@ -33,6 +34,8 @@ struct trace_eval_map {
> >
> > #define TRACEPOINT_DEFAULT_PRIO 10
> >
> > +extern struct srcu_struct tracepoint_srcu;
> > +
> > extern int
> > tracepoint_probe_register(struct tracepoint *tp, void *probe, void *data);
> > extern int
> > @@ -75,10 +78,15 @@ int unregister_tracepoint_module_notifier(struct
> > notifier_block *nb)
> > * probe unregistration and the end of module exit to make sure there is no
> > * caller executing a probe when it is freed.
> > */
> > +#ifdef CONFIG_TRACEPOINTS
> > static inline void tracepoint_synchronize_unregister(void)
> > {
> > + synchronize_srcu(&tracepoint_srcu);
> > synchronize_sched();
> > }
> > +#else
> > +static inline void tracepoint_synchronize_unregister(void) { }
>
> In order to add some consistency to the style in this header file,
> this empty function should look like:
>
> static inline void tracepoint_synchronize_unregister(void)
> { }
>
> (with newline before "{")
Ok, I changed it to the style you're proposing.
> > +#endif
> >
> > #ifdef CONFIG_HAVE_SYSCALL_TRACEPOINTS
> > extern int syscall_regfunc(void);
> > @@ -129,18 +137,38 @@ extern void syscall_unregfunc(void);
> > * as "(void *, void)". The DECLARE_TRACE_NOARGS() will pass in just
> > * "void *data", where as the DECLARE_TRACE() will pass in "void *data,
> > proto".
> > */
> > -#define __DO_TRACE(tp, proto, args, cond, rcucheck)
> > \
> > +#define __DO_TRACE(tp, proto, args, cond, rcuidle) \
> > do {\
> > struct tracepoint_func *it_func_ptr;\
> > void *it_func; \
> > void *__data; \
> > + int __maybe_unused idx = 0; \
> > \
> > if (!(cond))\
> > return; \
> > - if (rcucheck) \
> > - rcu_irq_enter_irqson(); \
> > - rcu_read_lock_sched_notrace(); \
> > - it_func_ptr = rcu_dereference_sched((tp)->funcs); \
> > + \
> > + /* \
> > +* For rcuidle callers, use srcu since sched-rcu\
> > +* doesn't work from the idle path.
Re: [PATCH v8 5/8] tracepoint: Make rcuidle tracepoint callers use SRCU
- On May 30, 2018, at 2:04 AM, Joel Fernandes joe...@google.com wrote:
> From: "Joel Fernandes (Google)"
>
> In recent tests with IRQ on/off tracepoints, a large performance
> overhead ~10% is noticed when running hackbench. This is root caused to
> calls to rcu_irq_enter_irqson and rcu_irq_exit_irqson from the
> tracepoint code. Following a long discussion on the list [1] about this,
> we concluded that srcu is a better alternative for use during rcu idle.
> Although it does involve extra barriers, its lighter than the sched-rcu
> version which has to do additional RCU calls to notify RCU idle about
> entry into RCU sections.
>
> In this patch, we change the underlying implementation of the
> trace_*_rcuidle API to use SRCU. This has shown to improve performance
> alot for the high frequency irq enable/disable tracepoints.
>
> Test: Tested idle and preempt/irq tracepoints.
>
> Here are some performance numbers:
>
> With a run of the following 30 times on a single core x86 Qemu instance
> with 1GB memory:
> hackbench -g 4 -f 2 -l 3000
>
> Completion times in seconds. CONFIG_PROVE_LOCKING=y.
>
> No patches (without this series)
> Mean: 3.048
> Median: 3.025
> Std Dev: 0.064
>
> With Lockdep using irq tracepoints with RCU implementation:
> Mean: 3.451 (-11.66 %)
> Median: 3.447 (-12.22%)
> Std Dev: 0.049
>
> With Lockdep using irq tracepoints with SRCU implementation (this series):
> Mean: 3.020 (I would consider the improvement against the "without
> this series" case as just noise).
> Median: 3.013
> Std Dev: 0.033
>
> [1] https://patchwork.kernel.org/patch/10344297/
>
> Signed-off-by: Joel Fernandes (Google)
> ---
> include/linux/tracepoint.h | 48 +++---
> kernel/tracepoint.c| 15 +++-
> 2 files changed, 54 insertions(+), 9 deletions(-)
>
> diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
> index c94f466d57ef..880794207921 100644
> --- a/include/linux/tracepoint.h
> +++ b/include/linux/tracepoint.h
> @@ -15,6 +15,7 @@
> */
>
> #include
> +#include
> #include
> #include
> #include
> @@ -33,6 +34,8 @@ struct trace_eval_map {
>
> #define TRACEPOINT_DEFAULT_PRIO 10
>
> +extern struct srcu_struct tracepoint_srcu;
> +
> extern int
> tracepoint_probe_register(struct tracepoint *tp, void *probe, void *data);
> extern int
> @@ -75,10 +78,15 @@ int unregister_tracepoint_module_notifier(struct
> notifier_block *nb)
> * probe unregistration and the end of module exit to make sure there is no
> * caller executing a probe when it is freed.
> */
> +#ifdef CONFIG_TRACEPOINTS
> static inline void tracepoint_synchronize_unregister(void)
> {
> + synchronize_srcu(&tracepoint_srcu);
> synchronize_sched();
> }
> +#else
> +static inline void tracepoint_synchronize_unregister(void) { }
In order to add some consistency to the style in this header file,
this empty function should look like:
static inline void tracepoint_synchronize_unregister(void)
{ }
(with newline before "{")
> +#endif
>
> #ifdef CONFIG_HAVE_SYSCALL_TRACEPOINTS
> extern int syscall_regfunc(void);
> @@ -129,18 +137,38 @@ extern void syscall_unregfunc(void);
> * as "(void *, void)". The DECLARE_TRACE_NOARGS() will pass in just
> * "void *data", where as the DECLARE_TRACE() will pass in "void *data,
> proto".
> */
> -#define __DO_TRACE(tp, proto, args, cond, rcucheck) \
> +#define __DO_TRACE(tp, proto, args, cond, rcuidle) \
> do {\
> struct tracepoint_func *it_func_ptr;\
> void *it_func; \
> void *__data; \
> + int __maybe_unused idx = 0; \
> \
> if (!(cond))\
> return; \
> - if (rcucheck) \
> - rcu_irq_enter_irqson(); \
> - rcu_read_lock_sched_notrace(); \
> - it_func_ptr = rcu_dereference_sched((tp)->funcs); \
> + \
> + /* \
> + * For rcuidle callers, use srcu since sched-rcu\
> + * doesn't work from the idle path. \
> + */ \
> + if (rcuidle) { \
> + if (in_nmi()) { \
> + WARN_ON_ONCE(1);\
> +
[PATCH v8 5/8] tracepoint: Make rcuidle tracepoint callers use SRCU
From: "Joel Fernandes (Google)"
In recent tests with IRQ on/off tracepoints, a large performance
overhead ~10% is noticed when running hackbench. This is root caused to
calls to rcu_irq_enter_irqson and rcu_irq_exit_irqson from the
tracepoint code. Following a long discussion on the list [1] about this,
we concluded that srcu is a better alternative for use during rcu idle.
Although it does involve extra barriers, its lighter than the sched-rcu
version which has to do additional RCU calls to notify RCU idle about
entry into RCU sections.
In this patch, we change the underlying implementation of the
trace_*_rcuidle API to use SRCU. This has shown to improve performance
alot for the high frequency irq enable/disable tracepoints.
Test: Tested idle and preempt/irq tracepoints.
Here are some performance numbers:
With a run of the following 30 times on a single core x86 Qemu instance
with 1GB memory:
hackbench -g 4 -f 2 -l 3000
Completion times in seconds. CONFIG_PROVE_LOCKING=y.
No patches (without this series)
Mean: 3.048
Median: 3.025
Std Dev: 0.064
With Lockdep using irq tracepoints with RCU implementation:
Mean: 3.451 (-11.66 %)
Median: 3.447 (-12.22%)
Std Dev: 0.049
With Lockdep using irq tracepoints with SRCU implementation (this series):
Mean: 3.020 (I would consider the improvement against the "without
this series" case as just noise).
Median: 3.013
Std Dev: 0.033
[1] https://patchwork.kernel.org/patch/10344297/
Signed-off-by: Joel Fernandes (Google)
---
include/linux/tracepoint.h | 48 +++---
kernel/tracepoint.c| 15 +++-
2 files changed, 54 insertions(+), 9 deletions(-)
diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index c94f466d57ef..880794207921 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -15,6 +15,7 @@
*/
#include
+#include
#include
#include
#include
@@ -33,6 +34,8 @@ struct trace_eval_map {
#define TRACEPOINT_DEFAULT_PRIO10
+extern struct srcu_struct tracepoint_srcu;
+
extern int
tracepoint_probe_register(struct tracepoint *tp, void *probe, void *data);
extern int
@@ -75,10 +78,15 @@ int unregister_tracepoint_module_notifier(struct
notifier_block *nb)
* probe unregistration and the end of module exit to make sure there is no
* caller executing a probe when it is freed.
*/
+#ifdef CONFIG_TRACEPOINTS
static inline void tracepoint_synchronize_unregister(void)
{
+ synchronize_srcu(&tracepoint_srcu);
synchronize_sched();
}
+#else
+static inline void tracepoint_synchronize_unregister(void) { }
+#endif
#ifdef CONFIG_HAVE_SYSCALL_TRACEPOINTS
extern int syscall_regfunc(void);
@@ -129,18 +137,38 @@ extern void syscall_unregfunc(void);
* as "(void *, void)". The DECLARE_TRACE_NOARGS() will pass in just
* "void *data", where as the DECLARE_TRACE() will pass in "void *data, proto".
*/
-#define __DO_TRACE(tp, proto, args, cond, rcucheck)\
+#define __DO_TRACE(tp, proto, args, cond, rcuidle) \
do {\
struct tracepoint_func *it_func_ptr;\
void *it_func; \
void *__data; \
+ int __maybe_unused idx = 0; \
\
if (!(cond))\
return; \
- if (rcucheck) \
- rcu_irq_enter_irqson(); \
- rcu_read_lock_sched_notrace(); \
- it_func_ptr = rcu_dereference_sched((tp)->funcs); \
+ \
+ /* \
+* For rcuidle callers, use srcu since sched-rcu\
+* doesn't work from the idle path. \
+*/ \
+ if (rcuidle) { \
+ if (in_nmi()) { \
+ WARN_ON_ONCE(1);\
+ return; /* no srcu from nmi */ \
+ } \
+ \
+ idx = srcu_read_lock_notrace(&tracepoint_srcu); \
+ it_func_ptr = \
+ srcu_dereference_notrace((tp)->funcs,
