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Message-ID: <36C68BD5-8FF4-4D2D-B35A-A94393EF6E24@fb.com>
Date: Mon, 12 Mar 2018 14:52:15 +0000
From: Song Liu <songliubraving@...com>
To: Peter Zijlstra <peterz@...radead.org>
CC: LKML <linux-kernel@...r.kernel.org>, Jiri Olsa <jolsa@...hat.com>,
"Kernel Team" <Kernel-team@...com>,
Ephraim Park <ephiepark@...com>, Tejun Heo <tj@...nel.org>,
Stephane Eranian <eranian@...gle.com>,
Lin Xiulei <linxiulei@...il.com>
Subject: Re: [PATCH] perf: update perf_cgroup time for ancestor cgroup(s)
> On Mar 12, 2018, at 5:38 AM, Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Sun, Mar 11, 2018 at 10:32:44PM -0700, Song Liu wrote:
>> When a perf_event is attached to parent cgroup, it should count events
>> for all children cgroups:
>>
>> parent_group <---- perf_event
>> \
>> - child_group <---- process(es)
>>
>> However, in our tests, we found this perf_event cannot report reliable
>> results. This is because perf_event->cgrp and cpuctx->cgrp are not
>> identical, thus perf_event->cgrp are not updated properly.
>
> It might help now and in for our older selves, if you could provide a
> simple reproducer for this.
I will add a repro to v2.
>
>> Signed-off-by: Song Liu <songliubraving@...com>
>> Reported-by: Ephraim Park <ephiepark@...com>
>> ---
>> kernel/events/core.c | 68 +++++++++++++++++++++++++++++++++++++++++++++++++++-
>> 1 file changed, 67 insertions(+), 1 deletion(-)
>>
>> diff --git a/kernel/events/core.c b/kernel/events/core.c
>> index 5789810..623d38f 100644
>> --- a/kernel/events/core.c
>> +++ b/kernel/events/core.c
>
>> @@ -766,6 +821,17 @@ perf_cgroup_set_timestamp(struct task_struct *task,
>> cgrp = perf_cgroup_from_task(task, ctx);
>> info = this_cpu_ptr(cgrp->info);
>> info->timestamp = ctx->timestamp;
>> +
>> + /* set timestamp for ancestor cgroups */
>> + if (cgrp->css.cgroup->level > 1) {
>> + struct perf_cgroup_info *info = this_cpu_ptr(cgrp->info);
>> + struct perf_event *event;
>> +
>> + list_for_each_entry(event, &ctx->pinned_groups, group_entry)
>> + perf_ancestor_cgroup_set_timestamp(event, cgrp, info);
>> + list_for_each_entry(event, &ctx->flexible_groups, group_entry)
>> + perf_ancestor_cgroup_set_timestamp(event, cgrp, info);
>> + }
>> }
>
> That doesn't make any kind of sense... if we're interested in ancestor
> groups, then WTH are you iterating _events_ ?
>
> I'm expecting something like:
>
> struct cgroup_subsys_state *css;
>
> for (css = cgrp->css; css; css = css->parent) {
> /* fudge time */
> }
I guess this is what I have been looking for! Thanks Peter!
V2 coming soon...
Song
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