Messages in this thread | | | From | Namhyung Kim <> | Date | Thu, 9 Dec 2021 13:51:42 -0800 | Subject | Re: [PATCH v3] perf/core: Set event shadow time for inactive events too |
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On Thu, Dec 9, 2021 at 3:35 AM Peter Zijlstra <peterz@infradead.org> wrote: > > On Thu, Dec 09, 2021 at 12:26:32PM +0100, Peter Zijlstra wrote: > > On Sun, Dec 05, 2021 at 02:48:43PM -0800, Namhyung Kim wrote: > > > > > Actually 18446744069443110306 is 0xffffffff01b345a2 so it seems to > > > have a negative enabled time. In fact, bperf keeps values returned by > > > bpf_perf_event_read_value() which calls perf_event_read_local(), and > > > accumulates delta between two calls. When event->shadow_ctx_time is > > > not set, it'd return invalid enabled time which is bigger than normal. > > > > *that*, how does it happen that shadow_time isn't set? It should be last > > set when the event switches to INACTIVE, no? At which point the logic in > > perf_event_read_local() should make @enabled move forward while @running > > stays put. > > > > Let me go rummage around a bit... either I'm missing something obvious > > or something's smelly. > > How's this then?
Still the same :(
Maybe because the event is enabled from the beginning. Then it might miss set_state/update_time at all.
> > diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h > index 7b7525e9155f..82baa8bdfc86 100644 > --- a/include/linux/perf_event.h > +++ b/include/linux/perf_event.h > @@ -686,9 +686,7 @@ struct perf_event { > /* > * timestamp shadows the actual context timing but it can > * be safely used in NMI interrupt context. It reflects the > - * context time as it was when the event was last scheduled in, > - * or when ctx_sched_in failed to schedule the event because we > - * run out of PMC. > + * context time as it was when the event was last scheduled in. > * > * ctx_time already accounts for ctx->timestamp. Therefore to > * compute ctx_time for a sample, simply add perf_clock(). > diff --git a/kernel/events/core.c b/kernel/events/core.c > index 28aaeacdaea1..20637b7f420c 100644 > --- a/kernel/events/core.c > +++ b/kernel/events/core.c > @@ -640,6 +640,9 @@ __perf_update_times(struct perf_event *event, u64 now, u64 *enabled, u64 *runnin > *running += delta; > } > > +static void perf_set_shadow_time(struct perf_event *event, > + struct perf_event_context *ctx); > + > static void perf_event_update_time(struct perf_event *event) > { > u64 now = perf_event_time(event); > @@ -647,6 +650,7 @@ static void perf_event_update_time(struct perf_event *event) > __perf_update_times(event, now, &event->total_time_enabled, > &event->total_time_running); > event->tstamp = now; > + perf_set_shadow_time(event, event->ctx);
I like this.
> } > > static void perf_event_update_sibling_time(struct perf_event *leader) > @@ -2552,8 +2556,6 @@ event_sched_in(struct perf_event *event, > > perf_pmu_disable(event->pmu); > > - perf_set_shadow_time(event, ctx); > - > perf_log_itrace_start(event); > > if (event->pmu->add(event, PERF_EF_START)) { > @@ -3707,29 +3709,6 @@ static noinline int visit_groups_merge(struct perf_cpu_context *cpuctx, > return 0; > } > > -static inline bool event_update_userpage(struct perf_event *event) > -{ > - if (likely(!atomic_read(&event->mmap_count))) > - return false; > - > - perf_event_update_time(event); > - perf_set_shadow_time(event, event->ctx); > - perf_event_update_userpage(event); > - > - return true; > -} > - > -static inline void group_update_userpage(struct perf_event *group_event) > -{ > - struct perf_event *event; > - > - if (!event_update_userpage(group_event)) > - return; > - > - for_each_sibling_event(event, group_event) > - event_update_userpage(event); > -} > - > static int merge_sched_in(struct perf_event *event, void *data) > { > struct perf_event_context *ctx = event->ctx; > @@ -3748,15 +3727,14 @@ static int merge_sched_in(struct perf_event *event, void *data) > } > > if (event->state == PERF_EVENT_STATE_INACTIVE) { > - *can_add_hw = 0; > if (event->attr.pinned) { > perf_cgroup_event_disable(event, ctx); > perf_event_set_state(event, PERF_EVENT_STATE_ERROR); > - } else { > - ctx->rotate_necessary = 1; > - perf_mux_hrtimer_restart(cpuctx); > - group_update_userpage(event); > } > + > + *can_add_hw = 0; > + ctx->rotate_necessary = 1; > + perf_mux_hrtimer_restart(cpuctx);
Not sure about this. We might not want to rotate them if a pinned event failed...?
Thanks, Namhyung
> } > > return 0; > @@ -6349,7 +6327,6 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma) > ring_buffer_attach(event, rb); > > perf_event_update_time(event); > - perf_set_shadow_time(event, event->ctx); > perf_event_init_userpage(event); > perf_event_update_userpage(event); > } else {
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