Re: [PATCH] sched: Combine ENQUEUE_MIGRATED check in activate_task()

[Zhongqiu Han]

On 7/25/2025 3:14 PM, K Prateek Nayak wrote:
> Hello Zhongqiu,
>
> On 7/24/2025 5:42 PM, Zhongqiu Han wrote:
> > Combine the task_on_rq_migrating() check and the sched_mm_cid_migrate_to()
> > invocation into a single conditional block. This removes a redundant flag
> > check and slightly reduces the instruction count in a hot path.
> >
> > Signed-off-by: Zhongqiu Han <quic_zhonhan@xxxxxxxxxxx>
> > ---
> > - This is a slight optimization and code cleanup, please let me know if you'd prefer to keep the current structure.
> > - Thanks
> >
> >   kernel/sched/core.c | 4 ++--
> >   1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index 2343f5691c54..d6063cf503ee 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -2118,10 +2118,10 @@ inline bool dequeue_task(struct rq *rq, struct task_struct *p, int flags)
> >   
> >   void activate_task(struct rq *rq, struct task_struct *p, int flags)
> >   {
> > -	if (task_on_rq_migrating(p))
> > +	if (task_on_rq_migrating(p)) {
> >   		flags |= ENQUEUE_MIGRATED;
> > -	if (flags & ENQUEUE_MIGRATED)
>
> I think "ENQUEUE_MIGRATED" can be individually set without
> task_on_rq_migrating() in the wakeup path via ttwu_do_activate().
>
> In that case "p->on_rq", goes from "0" to "TASK_ON_RQ_QUEUED" directly
> without going through an intermediate "TASK_ON_RQ_MIGRATING" but
> "ENQUEUE_MIGRATED" will be set if "p->task_cpu" was changed during
> wakeup.
Hi Prateek

You're right. Thanks for the nice review~



--
Thx and BRs,
Zhongqiu Han