Messages in this thread Patch in this message | | | Date | Sat, 4 Dec 2021 10:53:16 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH v2] sched/fair: Fix detection of per-CPU kthreads waking a task |
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On Wed, Dec 01, 2021 at 02:34:50PM +0000, Vincent Donnefort wrote: > select_idle_sibling() has a special case for tasks woken up by a per-CPU > kthread, where the selected CPU is the previous one. However, the current > condition for this exit path is incomplete. A task can wake up from an > interrupt context (e.g. hrtimer), while a per-CPU kthread is running. A > such scenario would spuriously trigger the special case described above. > Also, a recent change made the idle task like a regular per-CPU kthread, > hence making that situation more likely to happen > (is_per_cpu_kthread(swapper) being true now). > > Checking for task context makes sure select_idle_sibling() will not > interpret a wake up from any other context as a wake up by a per-CPU > kthread. > > Fixes: 52262ee567ad ("sched/fair: Allow a per-CPU kthread waking a task to stack on the same CPU, to fix XFS performance regression") > Signed-off-by: Vincent Donnefort <vincent.donnefort@arm.com> > ---
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 945d987246c5..56db4ae85995 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -6399,6 +6399,7 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target) > * pattern is IO completions. > */ > if (is_per_cpu_kthread(current) && > + in_task() && > prev == smp_processor_id() && > this_rq()->nr_running <= 1) { > return prev;
Hurmph, so now I have two 'trivial' patches from you that touch this same function and they's conflicting. I've fixed it up, but perhaps it would've been nice to have them combined in a series or somesuch :-)
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