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    SubjectRe: [PATCH v0 3/5] perf: Introduce instruction trace filtering
    Date
    Peter Zijlstra <peterz@infradead.org> writes:

    > On Fri, Dec 11, 2015 at 03:36:36PM +0200, Alexander Shishkin wrote:
    >> +static int __perf_event_itrace_filters_setup(void *info)
    >> +{
    >> + struct perf_event *event = info;
    >> + int ret;
    >> +
    >> + if (READ_ONCE(event->state) != PERF_EVENT_STATE_ACTIVE)
    >> + return -EAGAIN;
    >> +
    >> + /* matches smp_wmb() in event_sched_in() */
    >> + smp_rmb();
    >> +
    >> + /*
    >> + * There is a window with interrupts enabled before we get here,
    >> + * so we need to check again lest we try to stop another cpu's event.
    >> + */
    >> + if (READ_ONCE(event->oncpu) != smp_processor_id())
    >> + return -EAGAIN;
    >> +
    >> + event->pmu->stop(event, PERF_EF_UPDATE);
    >> + rcu_read_lock();
    >> + ret = event->pmu->itrace_filter_setup(event);
    >> + rcu_read_unlock();
    >> + event->pmu->start(event, PERF_EF_RELOAD);
    >
    > Would it not be more sensible to let the ::itrace_filter_setup() method
    > do the stop/start-ing if and when needed?

    Ok, so keeping in mind the other mails, if I add "int flags" to the
    signature and have it do the stop/start when called like

    event->pmu->itrace_filter_setup(event, PERF_EF_RELOAD);

    and not otherwise?

    Regards,
    --
    Alex


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