Messages in this thread | | | Date | Wed, 23 Mar 2022 21:07:01 +0800 | Subject | Re: [External] Re: [PATCH v2 2/6] perf/core: Introduce percpu perf_cgroup | From | Chengming Zhou <> |
| |
On 2022/3/23 8:51 下午, Peter Zijlstra wrote: > On Tue, Mar 22, 2022 at 08:08:30PM +0800, Chengming Zhou wrote: > >> diff --git a/kernel/events/core.c b/kernel/events/core.c >> index 8b5cf2aedfe6..848a3bfa9513 100644 >> --- a/kernel/events/core.c >> +++ b/kernel/events/core.c > >> @@ -843,11 +845,21 @@ static void perf_cgroup_switch(struct task_struct *task) >> */ >> local_irq_save(flags); >> >> + cgrp = perf_cgroup_from_task(task, NULL); >> + if (cgrp == __this_cpu_read(cpu_perf_cgroup)) >> + goto out; >> + >> + __this_cpu_write(cpu_perf_cgroup, cgrp); >> + >> list = this_cpu_ptr(&cgrp_cpuctx_list); >> list_for_each_entry_safe(cpuctx, tmp, list, cgrp_cpuctx_entry) { >> WARN_ON_ONCE(cpuctx->ctx.nr_cgroups == 0); >> >> perf_ctx_lock(cpuctx, cpuctx->task_ctx); >> + >> + if (cpuctx->cgrp == cgrp) >> + continue; >> + >> perf_pmu_disable(cpuctx->ctx.pmu); >> >> cpu_ctx_sched_out(cpuctx, EVENT_ALL); > > This is just straight up broken.. you can't continue after taking a > lock, that'll miss unlock.
Yes, Namhyung has pointed it out, I will fix it next version.
> > Also, I really don't see the point of cpu_perf_cgroup, cpuctx->cgrp > should be able to do this.
But the problem is that we have two cpuctx on the percpu list, do you mean we should use perf_cgroup of the first cpuctx to compare with the next task's perf_cgroup ?
Or we should delete the cgrp in cpuctx, and use this new percpu cpu_perf_cgroup?
> > Also, perhaps merge this in the previous patch, I'm not sure it makes > sense to split this.
Ok, will do. I put it in one patch in v1 RFC, then split it for easier review. I will put it together in the next version.
Thanks.
> > --- a/kernel/events/core.c > +++ b/kernel/events/core.c > @@ -833,6 +833,7 @@ static DEFINE_PER_CPU(struct list_head, > */ > static void perf_cgroup_switch(struct task_struct *task) > { > + struct perf_cgroup *cgrp; > struct perf_cpu_context *cpuctx, *tmp; > struct list_head *list; > unsigned long flags; > @@ -843,11 +844,20 @@ static void perf_cgroup_switch(struct ta > */ > local_irq_save(flags); > > + cgrp = perf_cgroup_from_task(task, NULL); > + > list = this_cpu_ptr(&cgrp_cpuctx_list); > list_for_each_entry_safe(cpuctx, tmp, list, cgrp_cpuctx_entry) { > WARN_ON_ONCE(cpuctx->ctx.nr_cgroups == 0); > > + if (READ_ONCE(cpuctx->cgrp == cgrp)) > + continue > + > perf_ctx_lock(cpuctx, cpuctx->task_ctx); > + > + if (cpuctx->cgrp == cgrp) > + goto next; > + > perf_pmu_disable(cpuctx->ctx.pmu); > > cpu_ctx_sched_out(cpuctx, EVENT_ALL); > @@ -855,50 +865,22 @@ static void perf_cgroup_switch(struct ta > * must not be done before ctxswout due > * to event_filter_match() in event_sched_out() > */ > - cpuctx->cgrp = perf_cgroup_from_task(task, > - &cpuctx->ctx); > + WRITE_ONCE(cpuctx->cgrp, cgrp); > /* > * set cgrp before ctxsw in to allow > * event_filter_match() to not have to pass > * task around > - * we pass the cpuctx->ctx to perf_cgroup_from_task() > - * because cgroup events are only per-cpu > */ > cpu_ctx_sched_in(cpuctx, EVENT_ALL, task); > > perf_pmu_enable(cpuctx->ctx.pmu); > +next: > perf_ctx_unlock(cpuctx, cpuctx->task_ctx); > } > > local_irq_restore(flags); > } > > -static inline void perf_cgroup_sched_switch(struct task_struct *task, > - struct task_struct *next) > -{ > - struct perf_cgroup *cgrp1; > - struct perf_cgroup *cgrp2 = NULL; > - > - rcu_read_lock(); > - /* > - * we come here when we know perf_cgroup_events > 0 > - * we do not need to pass the ctx here because we know > - * we are holding the rcu lock > - */ > - cgrp1 = perf_cgroup_from_task(task, NULL); > - cgrp2 = perf_cgroup_from_task(next, NULL); > - > - /* > - * only schedule out current cgroup events if we know > - * that we are switching to a different cgroup. Otherwise, > - * do no touch the cgroup events. > - */ > - if (cgrp1 != cgrp2) > - perf_cgroup_switch(task); > - > - rcu_read_unlock(); > -} > - > static int perf_cgroup_ensure_storage(struct perf_event *event, > struct cgroup_subsys_state *css) > { > @@ -1062,11 +1044,6 @@ static inline void update_cgrp_time_from > { > } > > -static inline void perf_cgroup_sched_switch(struct task_struct *task, > - struct task_struct *next) > -{ > -} > - > static inline int perf_cgroup_connect(pid_t pid, struct perf_event *event, > struct perf_event_attr *attr, > struct perf_event *group_leader) > @@ -1080,11 +1057,6 @@ perf_cgroup_set_timestamp(struct task_st > { > } > > -static inline void > -perf_cgroup_sched_switch(struct task_struct *task, struct task_struct *next) > -{ > -} > - > static inline u64 perf_cgroup_event_time(struct perf_event *event) > { > return 0; > @@ -1104,6 +1076,10 @@ static inline void > perf_cgroup_event_disable(struct perf_event *event, struct perf_event_context *ctx) > { > } > + > +static void perf_cgroup_switch(struct task_struct *task) > +{ > +} > #endif > > /* > @@ -3625,7 +3601,7 @@ void __perf_event_task_sched_out(struct > * cgroup event are system-wide mode only > */ > if (atomic_read(this_cpu_ptr(&perf_cgroup_events))) > - perf_cgroup_sched_switch(task, next); > + perf_cgroup_switch(next); > } > > /*
| |