Messages in this thread Patch in this message | | | From | Vincent Donnefort <> | Subject | [PATCH v2] sched/fair: Fix detection of per-CPU kthreads waking a task | Date | Wed, 1 Dec 2021 14:34:50 +0000 |
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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>
--- v1 -> v2: * is_idle_thread() -> in_task() to also include spurious detection when current != swapper. (Vincent Guittot) ---
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; -- 2.25.1
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