* [PATCH v1] sched: there is no need to call switch_mm_irqs_off when sched between two user thread.
@ 2022-05-31 11:56 Ming Wang
2022-05-31 14:46 ` Peter Zijlstra
0 siblings, 1 reply; 3+ messages in thread
From: Ming Wang @ 2022-05-31 11:56 UTC (permalink / raw)
To: Ingo Molnar, Peter Zijlstra, Juri Lelli, Vincent Guittot
Cc: Dietmar Eggemann, Steven Rostedt, Ben Segall, Mel Gorman,
Daniel Bristot de Oliveira, Valentin Schneider, linux-kernel
When condition (prev->active_mm == next->mm && !prev->mm) is met,
the situation is as follows:
user thread -> user thread
There is not need switch_mm when sched between two user thread.
Because they share the mm_struct. This can provide better
performance when testing UnixBench.
Signed-off-by: Ming Wang <wangming01@loongson.cn>
---
kernel/sched/core.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 696c649..9d7f6fb 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5099,7 +5099,8 @@ asmlinkage __visible void schedule_tail(struct task_struct *prev)
* case 'prev->active_mm == next->mm' through
* finish_task_switch()'s mmdrop().
*/
- switch_mm_irqs_off(prev->active_mm, next->mm, next);
+ if ((prev->active_mm != next->mm) || (!prev->mm))
+ switch_mm_irqs_off(prev->active_mm, next->mm, next);
if (!prev->mm) { // from kernel
/* will mmdrop() in finish_task_switch(). */
--
1.8.3.1
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: [PATCH v1] sched: there is no need to call switch_mm_irqs_off when sched between two user thread.
2022-05-31 11:56 [PATCH v1] sched: there is no need to call switch_mm_irqs_off when sched between two user thread Ming Wang
@ 2022-05-31 14:46 ` Peter Zijlstra
2022-06-01 6:45 ` Ming Wang
0 siblings, 1 reply; 3+ messages in thread
From: Peter Zijlstra @ 2022-05-31 14:46 UTC (permalink / raw)
To: Ming Wang
Cc: Ingo Molnar, Juri Lelli, Vincent Guittot, Dietmar Eggemann,
Steven Rostedt, Ben Segall, Mel Gorman,
Daniel Bristot de Oliveira, Valentin Schneider, linux-kernel
On Tue, May 31, 2022 at 07:56:41PM +0800, Ming Wang wrote:
> When condition (prev->active_mm == next->mm && !prev->mm) is met,
> the situation is as follows:
>
> user thread -> user thread
>
> There is not need switch_mm when sched between two user thread.
> Because they share the mm_struct. This can provide better
> performance when testing UnixBench.
>
> Signed-off-by: Ming Wang <wangming01@loongson.cn>
> ---
> kernel/sched/core.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 696c649..9d7f6fb 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -5099,7 +5099,8 @@ asmlinkage __visible void schedule_tail(struct task_struct *prev)
> * case 'prev->active_mm == next->mm' through
> * finish_task_switch()'s mmdrop().
> */
> - switch_mm_irqs_off(prev->active_mm, next->mm, next);
> + if ((prev->active_mm != next->mm) || (!prev->mm))
> + switch_mm_irqs_off(prev->active_mm, next->mm, next);
I think this needs to be inside switch_mm(). Architectures are free to
play silly games with what the current active mm is (and iirc x86
actually does this).
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH v1] sched: there is no need to call switch_mm_irqs_off when sched between two user thread.
2022-05-31 14:46 ` Peter Zijlstra
@ 2022-06-01 6:45 ` Ming Wang
0 siblings, 0 replies; 3+ messages in thread
From: Ming Wang @ 2022-06-01 6:45 UTC (permalink / raw)
To: Peter Zijlstra
Cc: Ingo Molnar, Juri Lelli, Vincent Guittot, Dietmar Eggemann,
Steven Rostedt, Ben Segall, Mel Gorman,
Daniel Bristot de Oliveira, Valentin Schneider, linux-kernel
On 2022/5/31 下午10:46, Peter Zijlstra wrote:
> On Tue, May 31, 2022 at 07:56:41PM +0800, Ming Wang wrote:
>> When condition (prev->active_mm == next->mm && !prev->mm) is met,
>> the situation is as follows:
>>
>> user thread -> user thread
>>
>> There is not need switch_mm when sched between two user thread.
>> Because they share the mm_struct. This can provide better
>> performance when testing UnixBench.
>>
>> Signed-off-by: Ming Wang <wangming01@loongson.cn>
>> ---
>> kernel/sched/core.c | 3 ++-
>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>> index 696c649..9d7f6fb 100644
>> --- a/kernel/sched/core.c
>> +++ b/kernel/sched/core.c
>> @@ -5099,7 +5099,8 @@ asmlinkage __visible void schedule_tail(struct task_struct *prev)
>> * case 'prev->active_mm == next->mm' through
>> * finish_task_switch()'s mmdrop().
>> */
>> - switch_mm_irqs_off(prev->active_mm, next->mm, next);
>> + if ((prev->active_mm != next->mm) || (!prev->mm))
>> + switch_mm_irqs_off(prev->active_mm, next->mm, next);
> I think this needs to be inside switch_mm(). Architectures are free to
> play silly games with what the current active mm is (and iirc x86
> actually does this).
ok, thanks! And I will do it in architecture code.
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2022-06-01 6:45 UTC | newest]
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2022-05-31 11:56 [PATCH v1] sched: there is no need to call switch_mm_irqs_off when sched between two user thread Ming Wang
2022-05-31 14:46 ` Peter Zijlstra
2022-06-01 6:45 ` Ming Wang
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