From: jun qian <[email protected]>
When the sched_schedstat changes from 0 to 1, some sched se maybe
already in the runqueue, the se->statistics.wait_start will be 0.
So it will let the (rq_of(cfs_rq)) - se->statistics.wait_start)
wrong. We need to avoid this scenario.
Signed-off-by: jun qian <[email protected]>
Signed-off-by: Yafang Shao <[email protected]>
---
kernel/sched/fair.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 658aa7a..dd7c3bb 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -908,6 +908,14 @@ static void update_curr_fair(struct rq *rq)
if (!schedstat_enabled())
return;
+ /*
+ * When the sched_schedstat changes from 0 to 1, some sched se maybe
+ * already in the runqueue, the se->statistics.wait_start will be 0.
+ * So it will let the delta wrong. We need to avoid this scenario.
+ */
+ if (unlikely(!schedstat_val(se->statistics.wait_start)))
+ return;
+
delta = rq_clock(rq_of(cfs_rq)) - schedstat_val(se->statistics.wait_start);
if (entity_is_task(se)) {
--
1.8.3.1
On Wed, Sep 30, 2020 at 10:47:12AM +0800, [email protected] wrote:
> From: jun qian <[email protected]>
>
> When the sched_schedstat changes from 0 to 1, some sched se maybe
> already in the runqueue, the se->statistics.wait_start will be 0.
> So it will let the (rq_of(cfs_rq)) - se->statistics.wait_start)
> wrong. We need to avoid this scenario.
Is this really the only problem there? Did you do a full audit of that
schedstat nonsense?
> Signed-off-by: jun qian <[email protected]>
> Signed-off-by: Yafang Shao <[email protected]>
> ---
> kernel/sched/fair.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 658aa7a..dd7c3bb 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -908,6 +908,14 @@ static void update_curr_fair(struct rq *rq)
your git-diff is 'funny', it got the function ^ wrong.
> if (!schedstat_enabled())
> return;
>
> + /*
> + * When the sched_schedstat changes from 0 to 1, some sched se maybe
> + * already in the runqueue, the se->statistics.wait_start will be 0.
> + * So it will let the delta wrong. We need to avoid this scenario.
> + */
> + if (unlikely(!schedstat_val(se->statistics.wait_start)))
> + return;
> +
> delta = rq_clock(rq_of(cfs_rq)) - schedstat_val(se->statistics.wait_start);
>
> if (entity_is_task(se)) {
> --
> 1.8.3.1
>
Peter Zijlstra <[email protected]> 于2020年9月30日周三 下午4:20写道：
>
> On Wed, Sep 30, 2020 at 10:47:12AM +0800, [email protected] wrote:
> > From: jun qian <[email protected]>
> >
> > When the sched_schedstat changes from 0 to 1, some sched se maybe
> > already in the runqueue, the se->statistics.wait_start will be 0.
> > So it will let the (rq_of(cfs_rq)) - se->statistics.wait_start)
> > wrong. We need to avoid this scenario.
>
> Is this really the only problem there? Did you do a full audit of that
> schedstat nonsense?
>
Did you mean that the sched_stat_xxx's xxx_start(sched_stat_sleep
sched_stat_iowait sched_stat_blocked
sched_stat_runtime) may be also depend the schedstat_enabled?
I have searched the codes, and found that these sched_stat_xxx's
xxx_start don't depend the schedstat_enabled
except the wait_start.
This patch is going to slove the problem that when the
schedstat_enabled is enabled, the sched_stat_wait of
the probed process will become unbelievable big probability in the fist time.
> > Signed-off-by: jun qian <[email protected]>
> > Signed-off-by: Yafang Shao <[email protected]>
> > ---
> > kernel/sched/fair.c | 8 ++++++++
> > 1 file changed, 8 insertions(+)
> >
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 658aa7a..dd7c3bb 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -908,6 +908,14 @@ static void update_curr_fair(struct rq *rq)
>
> your git-diff is 'funny', it got the function ^ wrong.
>
sorry :)
> > if (!schedstat_enabled())
> > return;
> >
> > + /*
> > + * When the sched_schedstat changes from 0 to 1, some sched se maybe
> > + * already in the runqueue, the se->statistics.wait_start will be 0.
> > + * So it will let the delta wrong. We need to avoid this scenario.
> > + */
> > + if (unlikely(!schedstat_val(se->statistics.wait_start)))
> > + return;
> > +
> > delta = rq_clock(rq_of(cfs_rq)) - schedstat_val(se->statistics.wait_start);
> >
> > if (entity_is_task(se)) {
> > --
> > 1.8.3.1
> >
On Wed, Sep 30, 2020 at 05:16:29PM +0800, jun qian wrote:
> Peter Zijlstra <[email protected]> 于2020年9月30日周三 下午4:20写道：
> >
> > On Wed, Sep 30, 2020 at 10:47:12AM +0800, [email protected] wrote:
> > > From: jun qian <[email protected]>
> > >
> > > When the sched_schedstat changes from 0 to 1, some sched se maybe
> > > already in the runqueue, the se->statistics.wait_start will be 0.
> > > So it will let the (rq_of(cfs_rq)) - se->statistics.wait_start)
> > > wrong. We need to avoid this scenario.
> >
> > Is this really the only problem there? Did you do a full audit of that
> > schedstat nonsense?
> >
>
> Did you mean that the sched_stat_xxx's xxx_start(sched_stat_sleep
> sched_stat_iowait sched_stat_blocked
> sched_stat_runtime) may be also depend the schedstat_enabled?
Yeah, this runtime schedstat_enabled thing is fairly recent, it used to
be an always on/off kinda thing.
At the time we figured inconsistencies from dynamically
enabling/disabling it were okay, it's just stats after all.
But if you now want to 'fix' that, then a full audit might be nice.
> I have searched the codes, and found that these sched_stat_xxx's
> xxx_start don't depend the schedstat_enabled
> except the wait_start.
OK, so you did the audit and only found this one issue? That's good
Changelog material :-)
Thanks!
Peter Zijlstra <[email protected]> 于2020年9月30日周三 下午5:57写道：
>
> On Wed, Sep 30, 2020 at 05:16:29PM +0800, jun qian wrote:
> > Peter Zijlstra <[email protected]> 于2020年9月30日周三 下午4:20写道：
> > >
> > > On Wed, Sep 30, 2020 at 10:47:12AM +0800, [email protected] wrote:
> > > > From: jun qian <[email protected]>
> > > >
> > > > When the sched_schedstat changes from 0 to 1, some sched se maybe
> > > > already in the runqueue, the se->statistics.wait_start will be 0.
> > > > So it will let the (rq_of(cfs_rq)) - se->statistics.wait_start)
> > > > wrong. We need to avoid this scenario.
> > >
> > > Is this really the only problem there? Did you do a full audit of that
> > > schedstat nonsense?
> > >
> >
> > Did you mean that the sched_stat_xxx's xxx_start(sched_stat_sleep
> > sched_stat_iowait sched_stat_blocked
> > sched_stat_runtime) may be also depend the schedstat_enabled?
>
> Yeah, this runtime schedstat_enabled thing is fairly recent, it used to
> be an always on/off kinda thing.
>
> At the time we figured inconsistencies from dynamically
> enabling/disabling it were okay, it's just stats after all.
>
> But if you now want to 'fix' that, then a full audit might be nice.
>
> > I have searched the codes, and found that these sched_stat_xxx's
> > xxx_start don't depend the schedstat_enabled
> > except the wait_start.
>
> OK, so you did the audit and only found this one issue? That's good
> Changelog material :-)
>
I found another problem, when the sched_schedstat changes from 1 to 0,
the sched se
which is already in the runqueue, the statistics.wait_start already
has a value. At this moment
sched_schedstat changes from 0 to 1 again, the (rq_of(cfs_rq)) -
se->statistics.wait_start)
will not be 0 and the wait time will be bigger than the real one. So
we need to modify the patch
to resolve the problem with this scenario.
So I really need a full audit might, ：-)
Thanks
> Thanks!
jun qian <[email protected]> 于2020年9月30日周三 下午9:08写道：
>
> Peter Zijlstra <[email protected]> 于2020年9月30日周三 下午5:57写道：
> >
> > On Wed, Sep 30, 2020 at 05:16:29PM +0800, jun qian wrote:
> > > Peter Zijlstra <[email protected]> 于2020年9月30日周三 下午4:20写道：
> > > >
> > > > On Wed, Sep 30, 2020 at 10:47:12AM +0800, [email protected] wrote:
> > > > > From: jun qian <[email protected]>
> > > > >
> > > > > When the sched_schedstat changes from 0 to 1, some sched se maybe
> > > > > already in the runqueue, the se->statistics.wait_start will be 0.
> > > > > So it will let the (rq_of(cfs_rq)) - se->statistics.wait_start)
> > > > > wrong. We need to avoid this scenario.
> > > >
> > > > Is this really the only problem there? Did you do a full audit of that
> > > > schedstat nonsense?
> > > >
> > >
> > > Did you mean that the sched_stat_xxx's xxx_start(sched_stat_sleep
> > > sched_stat_iowait sched_stat_blocked
> > > sched_stat_runtime) may be also depend the schedstat_enabled?
> >
> > Yeah, this runtime schedstat_enabled thing is fairly recent, it used to
> > be an always on/off kinda thing.
> >
> > At the time we figured inconsistencies from dynamically
> > enabling/disabling it were okay, it's just stats after all.
> >
> > But if you now want to 'fix' that, then a full audit might be nice.
> >
> > > I have searched the codes, and found that these sched_stat_xxx's
> > > xxx_start don't depend the schedstat_enabled
> > > except the wait_start.
> >
> > OK, so you did the audit and only found this one issue? That's good
> > Changelog material :-)
> >
>
> I found another problem, when the sched_schedstat changes from 1 to 0,
> the sched se
> which is already in the runqueue, the statistics.wait_start already
> has a value. At this moment
> sched_schedstat changes from 0 to 1 again, the (rq_of(cfs_rq)) -
> se->statistics.wait_start)
> will not be 0 and the wait time will be bigger than the real one. So
> we need to modify the patch
> to resolve the problem with this scenario.
>
hi Peter
I have sent another patch to improve the accuracy of sched_stat_wait
statistics.
I have no good idea to solve the another problem what i described up,
but the new
patch can improve the accuracy.
Thanks
> So I really need a full audit might, ：-)
>
> Thanks
>
> > Thanks!