2022-04-25 11:44:24

by Cruz Zhao

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

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 <[email protected]>
Signed-off-by: Cruz Zhao <[email protected]>
---
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

2022-04-25 11:57:17

by Peter Zijlstra

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

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.

2022-04-25 16:01:55

by Cruz Zhao

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

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