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Date: Wed, 05 Jan 2011 12:23:38 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: eranian@...gle.com
Cc: linux-kernel@...r.kernel.org, mingo@...e.hu, paulus@...ba.org,
davem@...emloft.net, fweisbec@...il.com,
perfmon2-devel@...ts.sf.net, eranian@...il.com,
robert.richter@....com, acme@...hat.com, lizf@...fujitsu.com
Subject: Re: [PATCH 4/5] perf_events: add cgroup support (v7)
On Mon, 2011-01-03 at 18:20 +0200, Stephane Eranian wrote:
> +#ifdef CONFIG_CGROUP_PERF
> +/*
> + * perf_cgroup_info keeps track of time_enabled for a cgroup.
> + * This is a per-cpu dynamically allocated data structure.
> + */
> +struct perf_cgroup_info {
> + u64 time;
> + u64 timestamp;
> +};
> +
> +struct perf_cgroup {
> + struct cgroup_subsys_state css;
> + struct perf_cgroup_info *info; /* timing info, one per cpu */
I think 'they' want a __percpu annotation there.
> +};
> +#endif
> diff --git a/kernel/perf_event.c b/kernel/perf_event.c
> index b782b7a..905b91a 100644
> --- a/kernel/perf_event.c
> +++ b/kernel/perf_event.c
> +static inline void __update_cgrp_time(struct perf_cgroup *cgrp)
> +{
> + struct perf_cgroup_info *t;
> + u64 now;
> +
> + now = perf_clock();
> +
> + t = per_cpu_ptr(cgrp->info, smp_processor_id());
this_cpu_ptr(cgrp->info);
> +
> + t->time += now - t->timestamp;
> + t->timestamp = now;
> +}
> +static inline void
> +perf_cgroup_set_timestamp(struct task_struct *task, u64 now)
> +{
> + struct perf_cgroup *cgrp;
> + struct perf_cgroup_info *info;
> +
> + if (!task)
> + return;
> +
> + cgrp = perf_cgroup_from_task(task);
> + info = per_cpu_ptr(cgrp->info, smp_processor_id());
this_cpu_ptr();
> + info->timestamp = now;
> +}
> +
> +/*
> + * called from perf_event_ask_sched_out() conditional to jump label
> + */
> +void
> +perf_cgroup_switch(struct task_struct *task, struct task_struct *next)
> +{
> + struct perf_cgroup *cgrp_out = perf_cgroup_from_task(task);
> + struct perf_cgroup *cgrp_in = perf_cgroup_from_task(next);
> + struct perf_cpu_context *cpuctx;
> + struct pmu *pmu;
> + /*
> + * if task is DEAD, then css_out is irrelevant, it has
> + * been changed to init_cgrp in cgroup_exit() from do_exit().
> + * Furthermore, perf_cgroup_exit_task(), has scheduled out
> + * all css constrained events, only unconstrained events
> + * remain. Therefore we need to reschedule based on css_in.
> + */
> + if (task->state != TASK_DEAD && cgrp_out == cgrp_in)
> + return;
I think that check is broken, TASK_DEAD is set way after calling
cgroup_exit(), so if we get preempted in between there you'll still go
funny.
We do set PF_EXITING before calling cgroup_exit() though.
> + rcu_read_lock();
> +
> + list_for_each_entry_rcu(pmu, &pmus, entry) {
> +
> + cpuctx = this_cpu_ptr(pmu->pmu_cpu_context);
> +
> + perf_pmu_disable(cpuctx->ctx.pmu);
> +
> + /*
> + * perf_cgroup_events says at least one
> + * context on this CPU has cgroup events.
> + *
> + * ctx->nr_cgroups reports the number of cgroup
> + * events for a context. Given there can be multiple
> + * PMUs, there can be multiple contexts.
> + */
> + if (cpuctx->ctx.nr_cgroups > 0) {
> + /*
> + * schedule out everything we have
> + * task == DEAD: only unconstrained events
> + * task != DEAD: css constrained + unconstrained events
> + *
Does this comment want an update? As per the above (broken) check, we
should never get here for DEAD tasks, hmm?
> + * We kick out all events (even if unconstrained)
> + * to allow the constrained events to be scheduled
> + * based on their position in the event list (fairness)
> + */
> + cpu_ctx_sched_out(cpuctx, EVENT_ALL);
> + /*
> + * reschedule css_in constrained + unconstrained events
> + */
> + cpu_ctx_sched_in(cpuctx, EVENT_ALL, next, 1);
> + }
> +
> + perf_pmu_enable(cpuctx->ctx.pmu);
> + }
> +
> + rcu_read_unlock();
> +}
> +
> +static inline void
Copy/paste fail?
> +perf_cgroup_exit_task(struct task_struct *task)
> +{
> +}
> +
> +static inline int perf_cgroup_connect(int fd, struct perf_event *event,
> + struct perf_event_attr *attr,
> + struct perf_event *group_leader)
Again, do we really need this 'inline' ?
> +{
> + struct perf_cgroup *cgrp;
> + struct cgroup_subsys_state *css;
> + struct file *file;
> + int ret = 0, fput_needed;
> +
> + file = fget_light(fd, &fput_needed);
> + if (!file)
> + return -EBADF;
> +
> + css = cgroup_css_from_dir(file, perf_subsys_id);
> + if (IS_ERR(css))
> + return PTR_ERR(css);
> +
> + cgrp = container_of(css, struct perf_cgroup, css);
> + event->cgrp = cgrp;
If we do that perf_get_cgroup() here (unconditional).
> + /*
> + * all events in a group must monitor
> + * the same cgroup because a thread belongs
> + * to only one perf cgroup at a time
> + */
> + if (group_leader && group_leader->cgrp != cgrp) {
> + perf_detach_cgroup(event);
> + ret = -EINVAL;
> + } else {
> + /* must be done before we fput() the file */
> + perf_get_cgroup(event);
> + }
Then you can have that conditional perf_detach_cgroup() here, right?
> + fput_light(file, fput_needed);
> + return ret;
> +}
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