[PATCH] sched/rt: Make update_curr_rt() more accurate

[PATCH] sched/rt: Make update_curr_rt() more accurate

[Wen Yang]

rq->clock_task may be updated between the two calls of 
rq_clock_task() in update_curr_rt(). Calling rq_clock_task() only
once makes it more accurate and efficient, taking update_curr() as
reference.

Signed-off-by: Wen Yang <wen.yang99@zte.com.cn>
Reviewed-by: Jiang Biao <jiang.biao2@zte.com.cn>
---
 kernel/sched/rt.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 4056c19..d6d2a65 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -950,12 +950,13 @@ static void update_curr_rt(struct rq *rq)
 {
 	struct task_struct *curr = rq->curr;
 	struct sched_rt_entity *rt_se = &curr->rt;
+	u64 now = rq_clock_task(rq);
 	u64 delta_exec;
 
 	if (curr->sched_class != &rt_sched_class)
 		return;
 
-	delta_exec = rq_clock_task(rq) - curr->se.exec_start;
+	delta_exec = now - curr->se.exec_start;
 	if (unlikely((s64)delta_exec <= 0))
 		return;
 
@@ -968,7 +969,7 @@ static void update_curr_rt(struct rq *rq)
 	curr->se.sum_exec_runtime += delta_exec;
 	account_group_exec_runtime(curr, delta_exec);
 
-	curr->se.exec_start = rq_clock_task(rq);
+	curr->se.exec_start = now;
 	cgroup_account_cputime(curr, delta_exec);
 
 	sched_rt_avg_update(rq, delta_exec);
-- 
1.9.1

Re: [PATCH] sched/rt: Make update_curr_rt() more accurate

[Peter Zijlstra]

On Mon, Feb 05, 2018 at 11:18:41AM +0800, Wen Yang wrote:
> rq->clock_task may be updated between the two calls of 
> rq_clock_task() in update_curr_rt(). Calling rq_clock_task() only
> once makes it more accurate and efficient, taking update_curr() as
> reference.
> 
> Signed-off-by: Wen Yang <wen.yang99@zte.com.cn>
> Reviewed-by: Jiang Biao <jiang.biao2@zte.com.cn>

Thanks!

Re: [PATCH] sched/rt: Make update_curr_rt() more accurate

[Peter Zijlstra]

On Mon, Feb 05, 2018 at 11:30:38AM +0100, Peter Zijlstra wrote:
> On Mon, Feb 05, 2018 at 11:18:41AM +0800, Wen Yang wrote:
> > rq->clock_task may be updated between the two calls of 
> > rq_clock_task() in update_curr_rt(). Calling rq_clock_task() only
> > once makes it more accurate and efficient, taking update_curr() as
> > reference.
> > 
> > Signed-off-by: Wen Yang <wen.yang99@zte.com.cn>
> > Reviewed-by: Jiang Biao <jiang.biao2@zte.com.cn>
> 
> Thanks!

I just noticed update_curr_dl() has the exact same issue, could you also
do a patch for that?

Re: [PATCH] sched/rt: Make update_curr_rt() more accurate

[Ingo Molnar]

* Wen Yang <wen.yang99@zte.com.cn> wrote:

> rq->clock_task may be updated between the two calls of 
> rq_clock_task() in update_curr_rt(). Calling rq_clock_task() only
> once makes it more accurate and efficient, taking update_curr() as
> reference.
> 
> Signed-off-by: Wen Yang <wen.yang99@zte.com.cn>
> Reviewed-by: Jiang Biao <jiang.biao2@zte.com.cn>
> ---
>  kernel/sched/rt.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index 4056c19..d6d2a65 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -950,12 +950,13 @@ static void update_curr_rt(struct rq *rq)
>  {
>  	struct task_struct *curr = rq->curr;
>  	struct sched_rt_entity *rt_se = &curr->rt;
> +	u64 now = rq_clock_task(rq);
>  	u64 delta_exec;
>  
>  	if (curr->sched_class != &rt_sched_class)
>  		return;
>  
> -	delta_exec = rq_clock_task(rq) - curr->se.exec_start;
> +	delta_exec = now - curr->se.exec_start;

Small nit: shouldn't we calculate 'now' after the return?

OTOH that 'return' should only be triggered statistically AFAICS, i.e. very 
rarely.

Thanks,

	Ingo

[tip:sched/urgent] sched/rt: Make update_curr_rt() more accurate

[tip-bot for Wen Yang]

Commit-ID:  e7ad203166fff89b1d8253faf68fbe6966bf7181
Gitweb:     https://git.kernel.org/tip/e7ad203166fff89b1d8253faf68fbe6966bf7181
Author:     Wen Yang <wen.yang99@zte.com.cn>
AuthorDate: Mon, 5 Feb 2018 11:18:41 +0800
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 6 Feb 2018 10:20:34 +0100

sched/rt: Make update_curr_rt() more accurate

rq->clock_task may be updated between the two calls of
rq_clock_task() in update_curr_rt(). Calling rq_clock_task() only
once makes it more accurate and efficient, taking update_curr() as
reference.

Signed-off-by: Wen Yang <wen.yang99@zte.com.cn>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Jiang Biao <jiang.biao2@zte.com.cn>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: zhong.weidong@zte.com.cn
Link: http://lkml.kernel.org/r/1517800721-42092-1-git-send-email-wen.yang99@zte.com.cn
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/sched/rt.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 89a086e..663b235 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -950,12 +950,13 @@ static void update_curr_rt(struct rq *rq)
 {
 	struct task_struct *curr = rq->curr;
 	struct sched_rt_entity *rt_se = &curr->rt;
+	u64 now = rq_clock_task(rq);
 	u64 delta_exec;
 
 	if (curr->sched_class != &rt_sched_class)
 		return;
 
-	delta_exec = rq_clock_task(rq) - curr->se.exec_start;
+	delta_exec = now - curr->se.exec_start;
 	if (unlikely((s64)delta_exec <= 0))
 		return;
 
@@ -968,7 +969,7 @@ static void update_curr_rt(struct rq *rq)
 	curr->se.sum_exec_runtime += delta_exec;
 	account_group_exec_runtime(curr, delta_exec);
 
-	curr->se.exec_start = rq_clock_task(rq);
+	curr->se.exec_start = now;
 	cgroup_account_cputime(curr, delta_exec);
 
 	sched_rt_avg_update(rq, delta_exec);

[tip:sched/urgent] sched/rt: Make update_curr_rt() more accurate

[tip-bot for Wen Yang]

Commit-ID:  a7711602c7b79950ea437178f601b52ab08ef659
Gitweb:     https://git.kernel.org/tip/a7711602c7b79950ea437178f601b52ab08ef659
Author:     Wen Yang <wen.yang99@zte.com.cn>
AuthorDate: Tue, 6 Feb 2018 09:53:28 +0800
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 13 Feb 2018 11:44:41 +0100

sched/rt: Make update_curr_rt() more accurate

rq->clock_task may be updated between the two calls of
rq_clock_task() in update_curr_rt(). Calling rq_clock_task() only
once makes it more accurate and efficient, taking update_curr() as
reference.

Signed-off-by: Wen Yang <wen.yang99@zte.com.cn>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Jiang Biao <jiang.biao2@zte.com.cn>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: zhong.weidong@zte.com.cn
Link: http://lkml.kernel.org/r/1517882008-44552-1-git-send-email-wen.yang99@zte.com.cn
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/sched/rt.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 663b235..aad49451 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -950,12 +950,13 @@ static void update_curr_rt(struct rq *rq)
 {
 	struct task_struct *curr = rq->curr;
 	struct sched_rt_entity *rt_se = &curr->rt;
-	u64 now = rq_clock_task(rq);
 	u64 delta_exec;
+	u64 now;
 
 	if (curr->sched_class != &rt_sched_class)
 		return;
 
+	now = rq_clock_task(rq);
 	delta_exec = now - curr->se.exec_start;
 	if (unlikely((s64)delta_exec <= 0))
 		return;