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Peter Zijlstra
b0ebeb5956
[ Upstream commitf06cc667f7] Namhyung reported thatbd27568117("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:bd27568117("perf: Rewrite core context handling") Reported-by: Namhyung Kim <namhyung@kernel.org> Debugged-by: Namhyung Kim <namhyung@kernel.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/20231009210425.GC6307@noisy.programming.kicks-ass.net Signed-off-by: Sasha Levin <sashal@kernel.org>
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