linux-kernel - Re: [RFC PATCH 1/2] perf_events: add support for per-cpu per-cgroup monitoring (v3)

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Date:	Thu, 9 Sep 2010 23:41:39 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	linux-kernel@...r.kernel.org, peterz@...radead.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
Subject: Re: [RFC PATCH 1/2] perf_events: add support for per-cpu per-cgroup
 monitoring (v3)

Eric,

On Thu, Sep 9, 2010 at 3:52 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> Le jeudi 09 septembre 2010 à 06:09 -0700, Stephane Eranian a écrit :
>> This kernel patch adds the ability to filter monitoring based on
>> container groups (cgroups). This is for use in per-cpu mode only.
>>
>> The patch adds perf_event_attr.cgroup, a boolean, to activate
>> this new mode. The cgroup is designated by passing in
>> perf_event_attr.cgroup_fd, an opened file descriptor to
>> the <mnt>/<cgroup>/perf_event.perf file.
>>
>> This is the second version of this patch. It corrects the way
>> time_enabled is accounted for. In cgroup mode, time_enabled reflects
>> the time the cgroup was active, i.e., threads from the cgroup executed
>> on the monitored CPU.  This is a more useful metric than just
>> wall-clock. The meaning of time_enabled without cgroup is unaffected.
>>
>> Signed-off-by: Stephane Eranian <eranian@...gle.com>
>
>
>> +#ifdef CONFIG_CGROUPS
>> +struct perf_cgroup_time {
>> +     u64 time;
>> +     u64 timestamp;
>> +};
>> +
>> +struct perf_cgroup {
>> +     struct cgroup_subsys_state css;
>> +     struct perf_cgroup_time *time;
>
>        struct perf_cgroup_time __percpu *time;
>
> Please run sparse  after this "__percpu" change.
>
>
Will do.

>> +     jc->time = alloc_percpu(struct perf_cgroup_time);
>> +     if (!jc->time) {
>> +             vfree(jc);
>> +             return ERR_PTR(-ENOMEM);
>> +     }
>> +
>> +     for_each_possible_cpu(c) {
>> +             t = per_cpu_ptr(jc->time, c);
>> +             t->time = 0;
>> +             t->timestamp = 0;
>> +     }
>
> alloc_percpu() is zalloc_percpu() in fact, memory is already cleared.
>
I remember thinking about this and trying to trace to the code down
to figure this out. But it is rather complicated. If alloc_percpu() always
clears the memory, then I think that calling is zalloc_percpu()
would be more helpful....

>
>
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