Re: [PATCH] perf/core: Introduce cpuctx->cgrp_ctx_list

[Peter Zijlstra]

On Tue, Oct 03, 2023 at 09:08:44PM -0700, Namhyung Kim wrote:

> But after the change, it ended up iterating all pmus/events in the cpu
> context if there's a cgroup event somewhere on the cpu context.
> Unfortunately it includes uncore pmus which have much longer latency to
> control.

Can you describe the problem in more detail please?

We have cgrp as part of the tree key: {cpu, pmu, cgroup, idx},
so it should be possible to find a specific cgroup for a cpu and or skip
to the next cgroup on that cpu in O(log n) time.

> To fix the issue, I restored a linked list equivalent to cgrp_cpuctx_list
> in the perf_cpu_context and link perf_cpu_pmu_contexts that have cgroup
> events only.  Also add new helpers to enable/disable and does ctx sched
> in/out for cgroups.

Adding a list and duplicating the whole scheduling infrastructure seems
'unfortunate' at best.