> On Mar 12, 2018, at 5:38 AM, Peter Zijlstra <pet...@infradead.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 <songliubrav...@fb.com>
>> Reported-by: Ephraim Park <ephiep...@fb.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
