Messages in this thread | | | Subject | Re: [PATCH v3 10/10] perf/cgroup: Do not switch system-wide events in cgroup switch | From | "Liang, Kan" <> | Date | Thu, 14 Nov 2019 10:16:53 -0500 |
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On 11/14/2019 8:57 AM, Peter Zijlstra wrote: > 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. > Why we want to switch !cgroup system-wide event in context switch?
How should current perf handle this case? For example, User A: perf stat -e cycles -G cgroup1 User B: perf stat -e instructions -a
There is only one cpuctx for each CPU. So both cycles and instructions are tracked in flexible_active list. When user A left, the cgroup context-switch schedule out everything including both cycles and instructions. It seems that we will never switch the instructions event back for user B.
Thanks, Kan
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