Messages in this thread Patch in this message | | | Subject | Re: [PATCH V7 07/14] perf/core: Add a new PERF_EV_CAP_COEXIST event capability | From | "Liang, Kan" <> | Date | Fri, 24 Jul 2020 09:43:44 -0400 |
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On 7/24/2020 7:46 AM, peterz@infradead.org wrote: > On Fri, Jul 24, 2020 at 12:55:43PM +0200, peterz@infradead.org wrote: >>> + 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. > > EXIT is difficult too.. Also, that COEXIST thing hurt my brian, can't we > do a simpler SIBLING thing that simply requires the event to be a group > sibling? > > The consequence is that SLOTS must be the leader, is that really a > problem? You keep providing the {cycles, slots, metric-things} example, > but afaict {slots, metric-thing, cycles} should work just fine too. > PERF_SAMPLE_READ with PERF_FORMAT_GROUP doesn't need to the the leader.
I'm not sure I get your point. For the PERF_SAMPLE_READ with PERF_FORMAT_GROUP case, other events can be the leader, e.g., {cycles, slots, metric-things}:S. In this case, the SLOTS event is not a leader. I don't think we can assume that the SLOTS event must be the leader.
I think the case should be a useful case. Users may want to read the Topdown values for each sample.
Thanks, Kan
> > The thing is, with COEXIST, if you have: > > {cycles, slots, metric1, metric2} > > and you say that COEXIST events need to co-exist with at least one other > COEXIST event you end up with a problem when: close(fd_slots) happens, > because in the above case, there's two more COEXIST events, so the > requirement holds, even through this is very much not what we want. > > You 'fixed' this by saying closing any COEXIST event will tear the group > up, but that's 'weird' and unexpected if you were to do: > close(fd_metric2). > > > So something like this. > > --- > Subject: perf/core: Add a new PERF_EV_CAP_SIBLING event capability > > Current perf assumes that events in a group are independent. Close an > event doesn't impact the value of the other events in the same group. > If the closed event is a member, after the event closure, other events > are still running like a group. If the closed event is a leader, other > events are running as singleton events. > > Add PERF_EV_CAP_SIBLING to allow events to indicate they require being > part of a group, and when the leader dies they cannot exist > independently. > > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> > --- > include/linux/perf_event.h | 4 ++++ > kernel/events/core.c | 38 +++++++++++++++++++++++++++++++++----- > 2 files changed, 37 insertions(+), 5 deletions(-) > > --- a/include/linux/perf_event.h > +++ b/include/linux/perf_event.h > @@ -576,9 +576,13 @@ typedef void (*perf_overflow_handler_t)( > * 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_SIBLING: An event with this flag must be a group sibling and > + * cannot be a group leader. If an event with this flag is detached from the > + * group it is scheduled out and moved into an unrecoverable ERROR state. > */ > #define PERF_EV_CAP_SOFTWARE BIT(0) > #define PERF_EV_CAP_READ_ACTIVE_PKG BIT(1) > +#define PERF_EV_CAP_SIBLING BIT(2) > > #define SWEVENT_HLIST_BITS 8 > #define SWEVENT_HLIST_SIZE (1 << SWEVENT_HLIST_BITS) > --- a/kernel/events/core.c > +++ b/kernel/events/core.c > @@ -2133,8 +2133,24 @@ static inline struct list_head *get_even > return event->attr.pinned ? &ctx->pinned_active : &ctx->flexible_active; > } > > +/* > + * Events that have PERF_EV_CAP_SIBLING require being part of a group and > + * cannot exist on their own, schedule them out and move them into the ERROR > + * state. Also see _perf_event_enable(), it will not be able to recover > + * this ERROR state. > + */ > +static inline void perf_remove_sibling_event(struct perf_event *event) > +{ > + struct perf_event_context *ctx = event->ctx; > + struct perf_cpu_context *cpuctx = __get_cpu_context(ctx); > + > + event_sched_out(event, cpuctx, ctx); > + perf_event_set_state(event, PERF_EVENT_STATE_ERROR); > +} > + > static void perf_group_detach(struct perf_event *event) > { > + struct perf_event *leader = event->group_leader; > struct perf_event *sibling, *tmp; > struct perf_event_context *ctx = event->ctx; > > @@ -2153,7 +2169,7 @@ static void perf_group_detach(struct per > /* > * If this is a sibling, remove it from its group. > */ > - if (event->group_leader != event) { > + if (leader != event) { > list_del_init(&event->sibling_list); > event->group_leader->nr_siblings--; > goto out; > @@ -2166,6 +2182,9 @@ static void perf_group_detach(struct per > */ > list_for_each_entry_safe(sibling, tmp, &event->sibling_list, sibling_list) { > > + if (sibling->event_caps & PERF_EV_CAP_SIBLING) > + perf_remove_sibling_event(sibling); > + > sibling->group_leader = sibling; > list_del_init(&sibling->sibling_list); > > @@ -2183,10 +2202,10 @@ static void perf_group_detach(struct per > } > > out: > - perf_event__header_size(event->group_leader); > - > - for_each_sibling_event(tmp, event->group_leader) > + for_each_sibling_event(tmp, leader) > perf_event__header_size(tmp); > + > + perf_event__header_size(leader); > } > > static bool is_orphaned_event(struct perf_event *event) > @@ -2979,6 +2998,7 @@ static void _perf_event_enable(struct pe > raw_spin_lock_irq(&ctx->lock); > if (event->state >= PERF_EVENT_STATE_INACTIVE || > event->state < PERF_EVENT_STATE_ERROR) { > +out: > raw_spin_unlock_irq(&ctx->lock); > return; > } > @@ -2990,8 +3010,16 @@ static void _perf_event_enable(struct pe > * has gone back into error state, as distinct from the task having > * been scheduled away before the cross-call arrived. > */ > - if (event->state == PERF_EVENT_STATE_ERROR) > + if (event->state == PERF_EVENT_STATE_ERROR) { > + /* > + * Detached SIBLING events cannot leave ERROR state. > + */ > + if (event->event_caps & PERF_EV_CAP_SIBLING && > + event->group_leader == event) > + goto out; > + > event->state = PERF_EVENT_STATE_OFF; > + } > raw_spin_unlock_irq(&ctx->lock); > > event_function_call(event, __perf_event_enable, NULL); >
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