Re: [PATCH 3/6] sched,perf,kvm: Fix preemption condition
From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: 2021-06-02 13:59:12
Also in:
dm-devel, kvm, linux-block, linux-fsdevel, linux-mm, linux-perf-users, linux-pm, linux-usb, lkml, netdev, rcu
----- On Jun 2, 2021, at 9:12 AM, Peter Zijlstra peterz@infradead.org wrote:
quoted hunk ↗ jump to hunk
When ran from the sched-out path (preempt_notifier or perf_event), p->state is irrelevant to determine preemption. You can get preempted with !task_is_running() just fine. The right indicator for preemption is if the task is still on the runqueue in the sched-out path. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> --- kernel/events/core.c | 7 +++---- virt/kvm/kvm_main.c | 2 +- 2 files changed, 4 insertions(+), 5 deletions(-)--- a/kernel/events/core.c +++ b/kernel/events/core.c@@ -8568,13 +8568,12 @@ static void perf_event_switch(struct tas}, }; - if (!sched_in && task->state == TASK_RUNNING) + if (!sched_in && current->on_rq) {
This changes from checking task->state to current->on_rq, but this change from "task" to "current" is not described in the commit message, which is odd. Are we really sure that task == current here ? Thanks, Mathieu
quoted hunk ↗ jump to hunk
switch_event.event_id.header.misc |= PERF_RECORD_MISC_SWITCH_OUT_PREEMPT; + } - perf_iterate_sb(perf_event_switch_output, - &switch_event, - NULL); + perf_iterate_sb(perf_event_switch_output, &switch_event, NULL); } /*--- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c@@ -4869,7 +4869,7 @@ static void kvm_sched_out(struct preempt{ struct kvm_vcpu *vcpu = preempt_notifier_to_vcpu(pn); - if (current->state == TASK_RUNNING) { + if (current->on_rq) { WRITE_ONCE(vcpu->preempted, true); WRITE_ONCE(vcpu->ready, true); }
-- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com