[PATCH v2] sched/core: Skip sched_core_fork/free() when core sched is disabled

[PATCH v2] sched/core: Skip sched_core_fork/free() when core sched is disabled

[Cruz Zhao]

As __put_task_struct() and copy_process() are hot path functions,
the call of sched_core_fork/free() will bring overhead when core
sched is disabled, and we skip them in these cases.

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Cruz Zhao <CruzZhao@linux.alibaba.com>
---
 kernel/sched/core_sched.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/core_sched.c b/kernel/sched/core_sched.c
index 38a2cec..72a8ef8 100644
--- a/kernel/sched/core_sched.c
+++ b/kernel/sched/core_sched.c
@@ -108,13 +108,16 @@ static unsigned long sched_core_clone_cookie(struct task_struct *p)
 
 void sched_core_fork(struct task_struct *p)
 {
-	RB_CLEAR_NODE(&p->core_node);
-	p->core_cookie = sched_core_clone_cookie(current);
+	if (!sched_core_disabled()) {
+		RB_CLEAR_NODE(&p->core_node);
+		p->core_cookie = sched_core_clone_cookie(current);
+	}
 }
 
 void sched_core_free(struct task_struct *p)
 {
-	sched_core_put_cookie(p->core_cookie);
+	if (!sched_core_disabled())
+		sched_core_put_cookie(p->core_cookie);
 }
 
 static void __sched_core_set(struct task_struct *p, unsigned long cookie)
-- 
1.8.3.1

Re: [PATCH v2] sched/core: Skip sched_core_fork/free() when core sched is disabled

[Peter Zijlstra]

On Mon, Apr 25, 2022 at 04:17:34AM +0800, Cruz Zhao wrote:
> As __put_task_struct() and copy_process() are hot path functions,
> the call of sched_core_fork/free() will bring overhead when core
> sched is disabled, and we skip them in these cases.

Only if you have profile data.. mostly these functions do whole lot of
nothing.

Re: [PATCH v2] sched/core: Skip sched_core_fork/free() when core sched is disabled

[cruzzhao]

在 2022/4/25 下午4:14, Peter Zijlstra 写道:
> On Mon, Apr 25, 2022 at 04:17:34AM +0800, Cruz Zhao wrote:
>> As __put_task_struct() and copy_process() are hot path functions,
>> the call of sched_core_fork/free() will bring overhead when core
>> sched is disabled, and we skip them in these cases.
> 
> Only if you have profile data.. mostly these functions do whole lot of
> nothing.

Many thanks for suggestion, I'll test it.

Best wishes,
Cruz Zhao