The idea here is we want to charge the scheduler-context task's
vruntime but charge the execution-context task's sum_exec_runtime.
This way cputime accounting goes against the task actually running
but vruntime accounting goes against the rq->donor task so we get
proper fairness.
Cc: Joel Fernandes <joelagnelf@nvidia.com>
Cc: Qais Yousef <qyousef@layalina.io>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ben Segall <bsegall@google.com>
Cc: Zimuzo Ezeozue <zezeozue@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Will Deacon <will@kernel.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Metin Kaya <Metin.Kaya@arm.com>
Cc: Xuewen Yan <xuewen.yan94@gmail.com>
Cc: K Prateek Nayak <kprateek.nayak@amd.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Suleiman Souhlal <suleiman@google.com>
Cc: kernel-team@android.com
Signed-off-by: John Stultz <jstultz@google.com>
---
kernel/sched/fair.c | 21 ++++++++++++++++-----
1 file changed, 16 insertions(+), 5 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index c798d27952431..f8ad3a44b3771 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1129,22 +1129,33 @@ static void update_tg_load_avg(struct cfs_rq *cfs_rq)
}
#endif /* CONFIG_SMP */
-static s64 update_curr_se(struct rq *rq, struct sched_entity *curr)
+static s64 update_curr_se(struct rq *rq, struct sched_entity *se)
{
u64 now = rq_clock_task(rq);
s64 delta_exec;
- delta_exec = now - curr->exec_start;
+ delta_exec = now - se->exec_start;
if (unlikely(delta_exec <= 0))
return delta_exec;
- curr->exec_start = now;
- curr->sum_exec_runtime += delta_exec;
+ se->exec_start = now;
+ if (entity_is_task(se)) {
+ struct task_struct *running = rq->curr;
+ /*
+ * If se is a task, we account the time against the running
+ * task, as w/ proxy-exec they may not be the same.
+ */
+ running->se.exec_start = now;
+ running->se.sum_exec_runtime += delta_exec;
+ } else {
+ /* If not task, account the time against se */
+ se->sum_exec_runtime += delta_exec;
+ }
if (schedstat_enabled()) {
struct sched_statistics *stats;
- stats = __schedstats_from_se(curr);
+ stats = __schedstats_from_se(se);
__schedstat_set(stats->exec_max,
max(delta_exec, stats->exec_max));
}
--
2.49.0.rc0.332.g42c0ae87b1-googHello John,
On 3/13/2025 3:41 AM, John Stultz wrote:
> The idea here is we want to charge the scheduler-context task's
> vruntime but charge the execution-context task's sum_exec_runtime.
>
> This way cputime accounting goes against the task actually running
> but vruntime accounting goes against the rq->donor task so we get
> proper fairness.
>
> Cc: Joel Fernandes <joelagnelf@nvidia.com>
> Cc: Qais Yousef <qyousef@layalina.io>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Juri Lelli <juri.lelli@redhat.com>
> Cc: Vincent Guittot <vincent.guittot@linaro.org>
> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
> Cc: Valentin Schneider <vschneid@redhat.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Ben Segall <bsegall@google.com>
> Cc: Zimuzo Ezeozue <zezeozue@google.com>
> Cc: Mel Gorman <mgorman@suse.de>
> Cc: Will Deacon <will@kernel.org>
> Cc: Waiman Long <longman@redhat.com>
> Cc: Boqun Feng <boqun.feng@gmail.com>
> Cc: "Paul E. McKenney" <paulmck@kernel.org>
> Cc: Metin Kaya <Metin.Kaya@arm.com>
> Cc: Xuewen Yan <xuewen.yan94@gmail.com>
> Cc: K Prateek Nayak <kprateek.nayak@amd.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
> Cc: Suleiman Souhlal <suleiman@google.com>
> Cc: kernel-team@android.com
> Signed-off-by: John Stultz <jstultz@google.com>
> ---
> kernel/sched/fair.c | 21 ++++++++++++++++-----
> 1 file changed, 16 insertions(+), 5 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index c798d27952431..f8ad3a44b3771 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -1129,22 +1129,33 @@ static void update_tg_load_avg(struct cfs_rq *cfs_rq)
> }
> #endif /* CONFIG_SMP */
>
> -static s64 update_curr_se(struct rq *rq, struct sched_entity *curr)
> +static s64 update_curr_se(struct rq *rq, struct sched_entity *se)
> {
> u64 now = rq_clock_task(rq);
> s64 delta_exec;
>
> - delta_exec = now - curr->exec_start;
> + delta_exec = now - se->exec_start;
> if (unlikely(delta_exec <= 0))
> return delta_exec;
>
> - curr->exec_start = now;
> - curr->sum_exec_runtime += delta_exec;
> + se->exec_start = now;
> + if (entity_is_task(se)) {
> + struct task_struct *running = rq->curr;
> + /*
> + * If se is a task, we account the time against the running
> + * task, as w/ proxy-exec they may not be the same.
> + */
> + running->se.exec_start = now;
> + running->se.sum_exec_runtime += delta_exec;
> + } else {
> + /* If not task, account the time against se */
> + se->sum_exec_runtime += delta_exec;
> + }
>
> if (schedstat_enabled()) {
> struct sched_statistics *stats;
>
> - stats = __schedstats_from_se(curr);
> + stats = __schedstats_from_se(se);
> __schedstat_set(stats->exec_max,
> max(delta_exec, stats->exec_max));
So I'm slightly confused here - For the case of proxy where
entity_is_task(), we charge the delta_exec to the running task's se but
then we go ahead and update the exec_max against the stats of the
donor's se? That seems odd.
Could we just replace the se with &rq->curr->se if entity_is_task()
returns true and keep the rest as is? The calculations will be same as
what it is above (except for the stats bit) and you'll not require
updating "exec_start" for both current task and proxy's se. Thoughts?
> }
--
Thanks and Regards,
Prateek
On Wed, 12 Mar 2025 15:11:34 -0700
John Stultz <jstultz@google.com> wrote:
> The idea here is we want to charge the scheduler-context task's
> vruntime but charge the execution-context task's sum_exec_runtime.
The "but" is confusing me. Do you mean, "and also"? The sentence
doesn't make sense with "but" unless it was:
"The idea here is we DON'T want to charge the scheduler-context
task's vruntime but charge the execution-context task's
sum_exec_runtime INSTEAD."
>
> This way cputime accounting goes against the task actually running
> but vruntime accounting goes against the rq->donor task so we get
> proper fairness.
But this shows that you want to do both, although, I would remove the
"but" here too. Replace it with "while".
Or maybe I'm just confused.
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index c798d27952431..f8ad3a44b3771 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -1129,22 +1129,33 @@ static void update_tg_load_avg(struct cfs_rq *cfs_rq)
> }
> #endif /* CONFIG_SMP */
>
> -static s64 update_curr_se(struct rq *rq, struct sched_entity *curr)
> +static s64 update_curr_se(struct rq *rq, struct sched_entity *se)
Should this be renamed to "update_se()" as it no longer appears to be
updating "curr_se".
> {
> u64 now = rq_clock_task(rq);
> s64 delta_exec;
>
> - delta_exec = now - curr->exec_start;
> + delta_exec = now - se->exec_start;
> if (unlikely(delta_exec <= 0))
> return delta_exec;
>
> - curr->exec_start = now;
> - curr->sum_exec_runtime += delta_exec;
> + se->exec_start = now;
> + if (entity_is_task(se)) {
> + struct task_struct *running = rq->curr;
> + /*
> + * If se is a task, we account the time against the running
> + * task, as w/ proxy-exec they may not be the same.
> + */
> + running->se.exec_start = now;
> + running->se.sum_exec_runtime += delta_exec;
> + } else {
> + /* If not task, account the time against se */
> + se->sum_exec_runtime += delta_exec;
> + }
Or maybe: update_proxy_se() ?
-- Steve
>
> if (schedstat_enabled()) {
> struct sched_statistics *stats;
>
> - stats = __schedstats_from_se(curr);
> + stats = __schedstats_from_se(se);
> __schedstat_set(stats->exec_max,
> max(delta_exec, stats->exec_max));
> }
On Thu, Mar 13, 2025 at 3:26 AM Steven Rostedt <rostedt@goodmis.org> wrote:
>
> On Wed, 12 Mar 2025 15:11:34 -0700
> John Stultz <jstultz@google.com> wrote:
>
> > The idea here is we want to charge the scheduler-context task's
> > vruntime but charge the execution-context task's sum_exec_runtime.
>
> The "but" is confusing me. Do you mean, "and also"? The sentence
> doesn't make sense with "but" unless it was:
>
> "The idea here is we DON'T want to charge the scheduler-context
> task's vruntime but charge the execution-context task's
> sum_exec_runtime INSTEAD."
>
> >
> > This way cputime accounting goes against the task actually running
> > but vruntime accounting goes against the rq->donor task so we get
> > proper fairness.
>
> But this shows that you want to do both, although, I would remove the
> "but" here too. Replace it with "while".
>
> Or maybe I'm just confused.
Apologies for beingconfusing. I know I can tangle my words sometimes. :)
Hrmm. I think maybe it's a bit more clear if I switch the order. ie:
Without proxy-exec, we normally charge the "current" task for both its
vruntime as well as its sum_exec_runtime.
With proxy, we want to charge the rq->curr (proxy/lock holder) time to
its sum_exec_runtime (so it's clear to userland the rq->curr task *is*
running).
*But*, instead of charging rq->curr for the vruntime, that is charged
against the rq->donor(lock waiter) task, because that is what it is
donating when it is used as the scheduler-context.
If the donor and curr tasks are the same, then it's the same as without proxy.
Your suggestion of "while" is good as well. I'll try to reword this.
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index c798d27952431..f8ad3a44b3771 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -1129,22 +1129,33 @@ static void update_tg_load_avg(struct cfs_rq *cfs_rq)
> > }
> > #endif /* CONFIG_SMP */
> >
> > -static s64 update_curr_se(struct rq *rq, struct sched_entity *curr)
> > +static s64 update_curr_se(struct rq *rq, struct sched_entity *se)
>
> Should this be renamed to "update_se()" as it no longer appears to be
> updating "curr_se".
>
> > {
> > u64 now = rq_clock_task(rq);
> > s64 delta_exec;
> >
> > - delta_exec = now - curr->exec_start;
> > + delta_exec = now - se->exec_start;
> > if (unlikely(delta_exec <= 0))
> > return delta_exec;
> >
> > - curr->exec_start = now;
> > - curr->sum_exec_runtime += delta_exec;
> > + se->exec_start = now;
> > + if (entity_is_task(se)) {
> > + struct task_struct *running = rq->curr;
> > + /*
> > + * If se is a task, we account the time against the running
> > + * task, as w/ proxy-exec they may not be the same.
> > + */
> > + running->se.exec_start = now;
> > + running->se.sum_exec_runtime += delta_exec;
> > + } else {
> > + /* If not task, account the time against se */
> > + se->sum_exec_runtime += delta_exec;
> > + }
>
> Or maybe: update_proxy_se() ?
I'm hesitant to call it update_proxy_se() since it's still used even
when proxy-exec isn't enabled.
update_se() could work, but also feels a little generic.
Maybe update_se_times()? or account_time_se()?
Appreciate the review and feedback!
thanks
-john
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