Messages in this thread | | | Date | Mon, 6 Dec 2021 09:57:47 +0000 | From | Vincent Donnefort <> | Subject | Re: [PATCH v2] sched/fair: Fix detection of per-CPU kthreads waking a task |
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On Sat, Dec 04, 2021 at 10:53:16AM +0100, Peter Zijlstra wrote: > 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 :-) >
I definitely should have created a single patchset. Apologies for the extra work and thanks for taking those two patches!
On another subject, in case you missed them, I also have two tiny fixes, reviewed by Vincent:
[PATCH v2 1/2] sched/fair: Fix asym_fits_capacity() task_util type [PATCH v2 2/2] sched/fair: Fix task_fits_capacity() capacity type
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