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    SubjectRe: [PATCH V7 07/14] perf/core: Add a new PERF_EV_CAP_COEXIST event capability
    On Thu, Jul 23, 2020 at 10:11:10AM -0700, kan.liang@linux.intel.com wrote:

    > diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
    > index 3b22db08b6fb..93631e5389bf 100644
    > --- a/include/linux/perf_event.h
    > +++ b/include/linux/perf_event.h
    > @@ -576,9 +576,14 @@ typedef void (*perf_overflow_handler_t)(struct perf_event *,
    > * PERF_EV_CAP_SOFTWARE: Is a software event.
    > * PERF_EV_CAP_READ_ACTIVE_PKG: A CPU event (or cgroup event) that can be read
    > * from any CPU in the package where it is active.
    > + * PERF_EV_CAP_COEXIST: An event with this flag must coexist with other sibling
    > + * events, which have the same flag. If any event with the flag is detached
    > + * from the group, split the group into singleton events, and move the events
    > + * with the flag to the unrecoverable ERROR state.
    > */
    > #define PERF_EV_CAP_SOFTWARE BIT(0)
    > #define PERF_EV_CAP_READ_ACTIVE_PKG BIT(1)
    > +#define PERF_EV_CAP_COEXIST BIT(2)
    >
    > #define SWEVENT_HLIST_BITS 8
    > #define SWEVENT_HLIST_SIZE (1 << SWEVENT_HLIST_BITS)
    > diff --git a/kernel/events/core.c b/kernel/events/core.c
    > index 7c436d705fbd..e35d549a356d 100644
    > --- a/kernel/events/core.c
    > +++ b/kernel/events/core.c
    > @@ -2133,10 +2133,28 @@ static inline struct list_head *get_event_list(struct perf_event *event)
    > return event->attr.pinned ? &ctx->pinned_active : &ctx->flexible_active;
    > }
    >
    > +/*
    > + * If the event has PERF_EV_CAP_COEXIST capability,
    > + * schedule it out and move it into the ERROR state.
    > + */
    > +static inline void perf_remove_coexist_events(struct perf_event *event)
    > +{
    > + struct perf_event_context *ctx = event->ctx;
    > + struct perf_cpu_context *cpuctx = __get_cpu_context(ctx);
    > +
    > + if (!(event->event_caps & PERF_EV_CAP_COEXIST))
    > + return;
    > +
    > + event_sched_out(event, cpuctx, ctx);
    > + perf_event_set_state(event, PERF_EVENT_STATE_ERROR);
    > +}

    Ah, so the problem here is that ERROR is actually recoverable using
    IOC_ENABLE. We don't want that either. Let me try and figure out of EXIT
    would work.

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