Messages in this thread | | | Date | Fri, 16 Dec 2022 19:25:25 +0800 | Subject | Re: [PATCH v2] perf/core: Fix cgroup events tracking | From | Chengming Zhou <> |
| |
Hello, ping :-)
On 2022/12/7 20:40, Chengming Zhou wrote: > We encounter perf warnings when using cgroup events like: > ``` > cd /sys/fs/cgroup > mkdir test > perf stat -e cycles -a -G test > ``` > > WARNING: CPU: 0 PID: 690 at kernel/events/core.c:849 perf_cgroup_switch+0xb2/0xc0 > Call Trace: > <TASK> > __schedule+0x4ae/0x9f0 > ? _raw_spin_unlock_irqrestore+0x23/0x40 > ? __cond_resched+0x18/0x20 > preempt_schedule_common+0x2d/0x70 > __cond_resched+0x18/0x20 > wait_for_completion+0x2f/0x160 > ? cpu_stop_queue_work+0x9e/0x130 > affine_move_task+0x18a/0x4f0 > > WARNING: CPU: 0 PID: 690 at kernel/events/core.c:829 ctx_sched_in+0x1cf/0x1e0 > Call Trace: > <TASK> > ? ctx_sched_out+0xb7/0x1b0 > perf_cgroup_switch+0x88/0xc0 > __schedule+0x4ae/0x9f0 > ? _raw_spin_unlock_irqrestore+0x23/0x40 > ? __cond_resched+0x18/0x20 > preempt_schedule_common+0x2d/0x70 > __cond_resched+0x18/0x20 > wait_for_completion+0x2f/0x160 > ? cpu_stop_queue_work+0x9e/0x130 > affine_move_task+0x18a/0x4f0 > > The above two warnings are not complete here since I remove other > unimportant information. The problem is caused by the perf cgroup > events tracking: > > CPU0 CPU1 > perf_event_open() > perf_event_alloc() > account_event() > account_event_cpu() > atomic_inc(perf_cgroup_events) > __perf_event_task_sched_out() > if (atomic_read(perf_cgroup_events)) > perf_cgroup_switch() > // kernel/events/core.c:849 > WARN_ON_ONCE(cpuctx->ctx.nr_cgroups == 0) > if (READ_ONCE(cpuctx->cgrp) == cgrp) // false > return > perf_ctx_lock() > ctx_sched_out() > cpuctx->cgrp = cgrp > ctx_sched_in() > perf_cgroup_set_timestamp() > // kernel/events/core.c:829 > WARN_ON_ONCE(!ctx->nr_cgroups) > perf_ctx_unlock() > perf_install_in_context() > cpu_function_call() > __perf_install_in_context() > add_event_to_ctx() > list_add_event() > perf_cgroup_event_enable() > ctx->nr_cgroups++ > cpuctx->cgrp = X > > We can see from above that we wrongly use percpu atomic perf_cgroup_events > to check if we need to perf_cgroup_switch(), which should only be used > when we know this CPU has cgroup events enabled. > > The commit bd2756811766 ("perf: Rewrite core context handling") change > to have only one context per-CPU, so we can just use cpuctx->cgrp to > check if this CPU has cgroup events enabled. > > So percpu atomic perf_cgroup_events is not needed. > > Fixes: bd2756811766 ("perf: Rewrite core context handling") > Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com> > Tested-by: Ravi Bangoria <ravi.bangoria@amd.com> > --- > v2: > - Remove timestamps and fix race graph in commit log per Ravi Bangoria. > - Add Fixes tag and Tested-by tag. > --- > kernel/events/core.c | 42 ++++++++++-------------------------------- > 1 file changed, 10 insertions(+), 32 deletions(-) > > diff --git a/kernel/events/core.c b/kernel/events/core.c > index eacc3702654d..5d97a9f26003 100644 > --- a/kernel/events/core.c > +++ b/kernel/events/core.c > @@ -380,7 +380,6 @@ enum event_type_t { > > /* > * perf_sched_events : >0 events exist > - * perf_cgroup_events: >0 per-cpu cgroup events exist on this cpu > */ > > static void perf_sched_delayed(struct work_struct *work); > @@ -389,7 +388,6 @@ static DECLARE_DELAYED_WORK(perf_sched_work, perf_sched_delayed); > static DEFINE_MUTEX(perf_sched_mutex); > static atomic_t perf_sched_count; > > -static DEFINE_PER_CPU(atomic_t, perf_cgroup_events); > static DEFINE_PER_CPU(struct pmu_event_list, pmu_sb_events); > > static atomic_t nr_mmap_events __read_mostly; > @@ -844,9 +842,16 @@ static void perf_cgroup_switch(struct task_struct *task) > struct perf_cpu_context *cpuctx = this_cpu_ptr(&perf_cpu_context); > struct perf_cgroup *cgrp; > > - cgrp = perf_cgroup_from_task(task, NULL); > + /* > + * cpuctx->cgrp is set when the first cgroup event enabled, > + * and is cleared when the last cgroup event disabled. > + */ > + if (READ_ONCE(cpuctx->cgrp) == NULL) > + return; > > WARN_ON_ONCE(cpuctx->ctx.nr_cgroups == 0); > + > + cgrp = perf_cgroup_from_task(task, NULL); > if (READ_ONCE(cpuctx->cgrp) == cgrp) > return; > > @@ -3631,8 +3636,7 @@ void __perf_event_task_sched_out(struct task_struct *task, > * to check if we have to switch out PMU state. > * cgroup event are system-wide mode only > */ > - if (atomic_read(this_cpu_ptr(&perf_cgroup_events))) > - perf_cgroup_switch(next); > + perf_cgroup_switch(next); > } > > static bool perf_less_group_idx(const void *l, const void *r) > @@ -4974,15 +4978,6 @@ static void unaccount_pmu_sb_event(struct perf_event *event) > detach_sb_event(event); > } > > -static void unaccount_event_cpu(struct perf_event *event, int cpu) > -{ > - if (event->parent) > - return; > - > - if (is_cgroup_event(event)) > - atomic_dec(&per_cpu(perf_cgroup_events, cpu)); > -} > - > #ifdef CONFIG_NO_HZ_FULL > static DEFINE_SPINLOCK(nr_freq_lock); > #endif > @@ -5048,8 +5043,6 @@ static void unaccount_event(struct perf_event *event) > schedule_delayed_work(&perf_sched_work, HZ); > } > > - unaccount_event_cpu(event, event->cpu); > - > unaccount_pmu_sb_event(event); > } > > @@ -11679,15 +11672,6 @@ static void account_pmu_sb_event(struct perf_event *event) > attach_sb_event(event); > } > > -static void account_event_cpu(struct perf_event *event, int cpu) > -{ > - if (event->parent) > - return; > - > - if (is_cgroup_event(event)) > - atomic_inc(&per_cpu(perf_cgroup_events, cpu)); > -} > - > /* Freq events need the tick to stay alive (see perf_event_task_tick). */ > static void account_freq_event_nohz(void) > { > @@ -11775,8 +11759,6 @@ static void account_event(struct perf_event *event) > } > enabled: > > - account_event_cpu(event, event->cpu); > - > account_pmu_sb_event(event); > } > > @@ -12822,13 +12804,11 @@ static void __perf_pmu_remove(struct perf_event_context *ctx, > > perf_event_groups_for_cpu_pmu(event, groups, cpu, pmu) { > perf_remove_from_context(event, 0); > - unaccount_event_cpu(event, cpu); > put_pmu_ctx(event->pmu_ctx); > list_add(&event->migrate_entry, events); > > for_each_sibling_event(sibling, event) { > perf_remove_from_context(sibling, 0); > - unaccount_event_cpu(sibling, cpu); > put_pmu_ctx(sibling->pmu_ctx); > list_add(&sibling->migrate_entry, events); > } > @@ -12847,7 +12827,6 @@ static void __perf_pmu_install_event(struct pmu *pmu, > > if (event->state >= PERF_EVENT_STATE_OFF) > event->state = PERF_EVENT_STATE_INACTIVE; > - account_event_cpu(event, cpu); > perf_install_in_context(ctx, event, cpu); > } > > @@ -13742,8 +13721,7 @@ static int __perf_cgroup_move(void *info) > struct task_struct *task = info; > > preempt_disable(); > - if (atomic_read(this_cpu_ptr(&perf_cgroup_events))) > - perf_cgroup_switch(task); > + perf_cgroup_switch(task); > preempt_enable(); > > return 0;
| |