lkml.org 
[lkml]   [2021]   [Jun]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Date
    From
    SubjectRe: [PATCH 3/6] sched,perf,kvm: Fix preemption condition
    ----- On Jun 2, 2021, at 9:12 AM, Peter Zijlstra peterz@infradead.org wrote:

    > 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

    > 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

    \
     
     \ /
      Last update: 2021-06-02 15:59    [W:4.617 / U:0.012 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site