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Subject[PATCH v1] sched: there is no need to call switch_mm_irqs_off when sched between two user thread.
Date
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
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