Re: Re: [PATCH v2 2/2] sched/fair: Fix premature check of WAKEUP_PREEMPTION

[Abel Wu]

On 2/28/25 10:26 PM, Vincent Guittot wrote:
> On Thu, 27 Feb 2025 at 09:58, Abel Wu <wuyun.abel@xxxxxxxxxxxxx> wrote:
> > The commit 6bc912b71b6f ("sched: SCHED_OTHER vs SCHED_IDLE isolation")
> > defines the behavior of SCHED_IDLE as following:
> >
> >   - no SCHED_IDLE buddies
> >   - never let SCHED_IDLE preempt on wakeup
> >   - always preempt SCHED_IDLE on wakeup
> >   - limit SLEEPER fairness for SCHED_IDLE
> >
> > and the 3rd rule is broken if !WAKEUP_PREEMPTION due to recently merged
> > commit faa42d29419d ("sched/fair: Make SCHED_IDLE entity be preempted in strict hierarchy")
> >
> > Although WAKEUP_PREEMPTION is mainly there for debug purpose to provide
> > a way to check whether a performance degrade of certain workload is due
> > to overscheduling or not, it is still kind of weird that we treat sched-
> > idle cpus as idle but don't let the non-idle tasks preempt the sched-idle
> > cpus in debug mode (!WAKEUP_PREEMPTION).
> >
> > Fix it by strictly following the aforementioned rules.
> >
> > Fixes: faa42d29419d ("sched/fair: Make SCHED_IDLE entity be preempted in strict hierarchy")
> > Signed-off-by: Abel Wu <wuyun.abel@xxxxxxxxxxxxx>
>
> WAKEUP_PREEMPTION seems to be still used so
>
> Acked-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>

Thanks!