From f06cc667f79909e9175460b167c277b7c64d3df0 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Mon, 9 Oct 2023 23:04:25 +0200 Subject: perf: Optimize perf_cgroup_switch() Namhyung reported that bd2756811766 ("perf: Rewrite core context handling") regresses context switch overhead when perf-cgroup is in use together with 'slow' PMUs like uncore. Specifically, perf_cgroup_switch()'s perf_ctx_disable() / ctx_sched_out() etc.. all iterate the full list of active PMUs for that CPU, even if they don't have cgroup events. Previously there was cgrp_cpuctx_list which linked the relevant PMUs together, but that got lost in the rework. Instead of re-instruducing a similar list, let the perf_event_pmu_context iteration skip those that do not have cgroup events. This avoids growing multiple versions of the perf_event_pmu_context iteration. Measured performance (on a slightly different patch): Before) $ taskset -c 0 ./perf bench sched pipe -l 10000 -G AAA,BBB # Running 'sched/pipe' benchmark: # Executed 10000 pipe operations between two processes Total time: 0.901 [sec] 90.128700 usecs/op 11095 ops/sec After) $ taskset -c 0 ./perf bench sched pipe -l 10000 -G AAA,BBB # Running 'sched/pipe' benchmark: # Executed 10000 pipe operations between two processes Total time: 0.065 [sec] 6.560100 usecs/op 152436 ops/sec Fixes: bd2756811766 ("perf: Rewrite core context handling") Reported-by: Namhyung Kim Debugged-by: Namhyung Kim Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20231009210425.GC6307@noisy.programming.kicks-ass.net --- include/linux/perf_event.h | 1 + 1 file changed, 1 insertion(+) (limited to 'include/linux') diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h index f31f962a6445..0367d748fae0 100644 --- a/include/linux/perf_event.h +++ b/include/linux/perf_event.h @@ -878,6 +878,7 @@ struct perf_event_pmu_context { unsigned int embedded : 1; unsigned int nr_events; + unsigned int nr_cgroups; atomic_t refcount; /* event <-> epc */ struct rcu_head rcu_head; -- cgit v1.2.3