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SubjectRe: [PATCH v3 10/10] perf/cgroup: Do not switch system-wide events in cgroup switch
On Thu, Nov 14, 2019 at 08:46:51AM -0500, Liang, Kan wrote:
>
>
> On 11/14/2019 5:43 AM, Peter Zijlstra wrote:
> > On Wed, Nov 13, 2019 at 04:30:42PM -0800, Ian Rogers wrote:
> > > From: Kan Liang <kan.liang@linux.intel.com>
> > >
> > > When counting system-wide events and cgroup events simultaneously, the
> > > system-wide events are always scheduled out then back in during cgroup
> > > switches, bringing extra overhead and possibly missing events. Switching
> > > out system wide flexible events may be necessary if the scheduled in
> > > task's cgroups have pinned events that need to be scheduled in at a higher
> > > priority than the system wide flexible events.
> >
> > I'm thinking this patch is actively broken. groups->index 'group' wide
> > and therefore across cpu/cgroup boundaries.
> >
> > There is no !cgroup to cgroup hierarchy as this patch seems to assume,
> > specifically look at how the merge sort in visit_groups_merge() allows
> > cgroup events to be picked before !cgroup events.
>
>
> No, the patch intends to avoid switch !cgroup during cgroup context switch.

Which is wrong.

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