Re: [RFC 2/2] perf/core: Invoke pmu::sched_task callback for per-cpu events

Namhyung Kim
2020-11-05T15:54:29Z

On Thu, Nov 5, 2020 at 11:48 PM Liang, Kan <kan.liang@linux.intel.com> wrote:
>
>
>
> On 11/2/2020 9:52 AM, Namhyung Kim wrote:
> > The commit 44fae179ce73 ("perf/core: Pull pmu::sched_task() into
> > perf_event_context_sched_out()") moved the pmu::sched_task callback to
> > be called for task event context. But it missed to call it for
> > per-cpu events to flush PMU internal buffers (i.e. for PEBS, ...).
> >
> > This commit basically reverts the commit but keeps the optimization
> > for task events and only add missing calls for cpu events.
> >
> > Fixes: 44fae179ce73 ("perf/core: Pull pmu::sched_task() into perf_event_context_sched_out()")
> > Signed-off-by: Namhyung Kim <namhyung@kernel.org>
> > ---
[SNIP]
> > @@ -3850,6 +3880,9 @@ void __perf_event_task_sched_in(struct task_struct *prev,
> >
> > if (atomic_read(&nr_switch_events))
> > perf_event_switch(task, prev, true);
> > +
> > + if (__this_cpu_read(perf_sched_cb_usages))
> > + perf_pmu_sched_task(prev, task, true);
> > }
>
> It looks like the ("perf/core: Pull pmu::sched_task() into
> perf_event_context_sched_in()") is also reverted in the patch.

Ah, right..

>
> >
> > static u64 perf_calculate_period(struct perf_event *event, u64 nsec, u64 count)
> > @@ -12999,6 +13032,7 @@ static void __init perf_event_init_all_cpus(void)
> > #ifdef CONFIG_CGROUP_PERF
> > INIT_LIST_HEAD(&per_cpu(cgrp_cpuctx_list, cpu));
> > #endif
> > + INIT_LIST_HEAD(&per_cpu(sched_cb_list, cpu));
> > }
> > }
> >
> >
>
> Can we only update the perf_sched_cb_usages and sched_cb_list for
> per-cpu event as below patch (not tested)?
>
> If user only uses the per-process event, we don't need to go through the
> list.

Hmm... ok.

>
>
> diff --git a/arch/powerpc/perf/core-book3s.c
> b/arch/powerpc/perf/core-book3s.c
> index 6586f7e71cfb..63c9b87cab5e 100644
> --- a/arch/powerpc/perf/core-book3s.c
> +++ b/arch/powerpc/perf/core-book3s.c
> @@ -380,7 +380,7 @@ static void power_pmu_bhrb_enable(struct perf_event
> *event)
> cpuhw->bhrb_context = event->ctx;
> }
> cpuhw->bhrb_users++;
> - perf_sched_cb_inc(event->ctx->pmu);
> + perf_sched_cb_inc(event->ctx->pmu, !(event->attach_state &
> PERF_ATTACH_TASK));
> }
>
> static void power_pmu_bhrb_disable(struct perf_event *event)
> diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c
> index 444e5f061d04..a34b90c7fa6d 100644
> --- a/arch/x86/events/intel/ds.c
> +++ b/arch/x86/events/intel/ds.c
> @@ -1022,9 +1022,9 @@ pebs_update_state(bool needed_cb, struct
> cpu_hw_events *cpuc,
>
> if (needed_cb != pebs_needs_sched_cb(cpuc)) {
> if (!needed_cb)
> - perf_sched_cb_inc(pmu);
> + perf_sched_cb_inc(pmu, !(event->attach_state & PERF_ATTACH_TASK));
> else
> - perf_sched_cb_dec(pmu);
> + perf_sched_cb_dec(pmu, !(event->attach_state & PERF_ATTACH_TASK));
>
> update = true;
> }
> diff --git a/arch/x86/events/intel/lbr.c b/arch/x86/events/intel/lbr.c
> index 8961653c5dd2..8d4d02cde3d4 100644
> --- a/arch/x86/events/intel/lbr.c
> +++ b/arch/x86/events/intel/lbr.c
> @@ -693,7 +693,7 @@ void intel_pmu_lbr_add(struct perf_event *event)
> */
> if (x86_pmu.intel_cap.pebs_baseline && event->attr.precise_ip > 0)
> cpuc->lbr_pebs_users++;
> - perf_sched_cb_inc(event->ctx->pmu);
> + perf_sched_cb_inc(event->ctx->pmu, !(event->attach_state &
> PERF_ATTACH_TASK));
> if (!cpuc->lbr_users++ && !event->total_time_running)
> intel_pmu_lbr_reset();
>
> @@ -740,7 +740,7 @@ void intel_pmu_lbr_del(struct perf_event *event)
> cpuc->lbr_users--;
> WARN_ON_ONCE(cpuc->lbr_users < 0);
> WARN_ON_ONCE(cpuc->lbr_pebs_users < 0);
> - perf_sched_cb_dec(event->ctx->pmu);
> + perf_sched_cb_dec(event->ctx->pmu, !(event->attach_state &
> PERF_ATTACH_TASK));
> }
>
> static inline bool vlbr_exclude_host(void)
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index abb70a557cb5..5a02239ca8fd 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -966,8 +966,8 @@ extern const struct perf_event_attr
> *perf_event_attrs(struct perf_event *event);
> extern void perf_event_print_debug(void);
> extern void perf_pmu_disable(struct pmu *pmu);
> extern void perf_pmu_enable(struct pmu *pmu);
> -extern void perf_sched_cb_dec(struct pmu *pmu);
> -extern void perf_sched_cb_inc(struct pmu *pmu);
> +extern void perf_sched_cb_dec(struct pmu *pmu, bool systemwide);
> +extern void perf_sched_cb_inc(struct pmu *pmu, bool systemwide);
> extern int perf_event_task_disable(void);
> extern int perf_event_task_enable(void);
>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index e6b98507734a..2d7c07af02f8 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -3484,25 +3484,29 @@ static void perf_event_context_sched_out(struct
> task_struct *task, int ctxn,
>
> static DEFINE_PER_CPU(struct list_head, sched_cb_list);
>
> -void perf_sched_cb_dec(struct pmu *pmu)
> +void perf_sched_cb_dec(struct pmu *pmu, bool systemwide)
> {
> struct perf_cpu_context *cpuctx = this_cpu_ptr(pmu->pmu_cpu_context);
>
> - this_cpu_dec(perf_sched_cb_usages);
> + --cpuctx->sched_cb_usage;
>
> - if (!--cpuctx->sched_cb_usage)
> + if (systemwide) {
> + this_cpu_dec(perf_sched_cb_usages);
> list_del(&cpuctx->sched_cb_entry);
> + }
> }
>
>
> -void perf_sched_cb_inc(struct pmu *pmu)
> +void perf_sched_cb_inc(struct pmu *pmu, bool systemwide)
> {
> struct perf_cpu_context *cpuctx = this_cpu_ptr(pmu->pmu_cpu_context);
>
> - if (!cpuctx->sched_cb_usage++)
> - list_add(&cpuctx->sched_cb_entry, this_cpu_ptr(&sched_cb_list));
> + cpuctx->sched_cb_usage++;
>
> - this_cpu_inc(perf_sched_cb_usages);
> + if (systemwide) {
> + this_cpu_inc(perf_sched_cb_usages);
> + list_add(&cpuctx->sched_cb_entry, this_cpu_ptr(&sched_cb_list));

You need to check the value and make sure it's added only once.

Thanks
Namhyung

> + }
> }
>
> /*
>
> Thanks,
> Kan