Messages in this thread Patch in this message | | | Date | Thu, 9 Dec 2021 12:34:48 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH v3] perf/core: Set event shadow time for inactive events too |
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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?
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); } 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); } 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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