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authorDavid Carrillo-Cisneros <davidcc@google.com>2017-01-18 22:24:53 +0300
committerIngo Molnar <mingo@kernel.org>2017-01-30 14:01:13 +0300
commit058fe1c0440e68a1ba3c2270ae43e9f0298b27d8 (patch)
treecc8ea7d1890dbfdcc62b9fdf5e73e7a243a875a2 /include/linux/perf_event.h
parentae5112a825ac7460c0c2c6c3daf21142c741d058 (diff)
downloadlinux-058fe1c0440e68a1ba3c2270ae43e9f0298b27d8.tar.xz
perf/core: Make cgroup switch visit only cpuctxs with cgroup events
This patch follows from a conversation in CQM/CMT's last series about speeding up the context switch for cgroup events: https://patchwork.kernel.org/patch/9478617/ This is a low-hanging fruit optimization. It replaces the iteration over the "pmus" list in cgroup switch by an iteration over a new list that contains only cpuctxs with at least one cgroup event. This is necessary because the number of PMUs have increased over the years e.g modern x86 server systems have well above 50 PMUs. The iteration over the full PMU list is unneccessary and can be costly in heavy cache contention scenarios. Below are some instrumentation measurements with 10, 50 and 90 percentiles of the total cost of context switch before and after this optimization for a simple array read/write microbenchark. Contention Level Nr events Before (us) After (us) Median L2 L3 types (10%, 50%, 90%) (10%, 50%, 90% Speedup -------------------------------------------------------------------------- Low Low 1 (1.72, 2.42, 5.85) (1.35, 1.64, 5.46) 29% High Low 1 (2.08, 4.56, 19.8) (1720, 2.20, 13.7) 51% High High 1 (2.86, 10.4, 12.7) (2.54, 4.32, 12.1) 58% Low Low 2 (1.98, 3.20, 6.89) (1.68, 2.41, 8.89) 24% High Low 2 (2.48, 5.28, 22.4) (2150, 3.69, 14.6) 30% High High 2 (3.32, 8.09, 13.9) (2.80, 5.15, 13.7) 36% where: 1 event type = cycles 2 event types = cycles,intel_cqm/llc_occupancy/ Contention L2 Low: workset < L2 cache size. High: " >> L2 " " . Contention L3 Low: workset of task on all sockets < L3 cache size. High: " " " " " " >> L3 " " . Median Speedup is (50%ile Before - 50%ile After) / 50%ile Before Unsurprisingly, the benefits of this optimization decrease with the number of cpuctxs with a cgroup events, yet, is never detrimental. Tested-by: Mark Rutland <mark.rutland@arm.com> Signed-off-by: David Carrillo-Cisneros <davidcc@google.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Mark Rutland <mark.rutland@arm.com> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> Cc: Arnaldo Carvalho de Melo <acme@kernel.org> Cc: Arnaldo Carvalho de Melo <acme@redhat.com> Cc: Borislav Petkov <bp@suse.de> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Jiri Olsa <jolsa@redhat.com> Cc: Kan Liang <kan.liang@intel.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul Turner <pjt@google.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com> Cc: Stephane Eranian <eranian@google.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Vikas Shivappa <vikas.shivappa@linux.intel.com> Cc: Vince Weaver <vince@deater.net> Cc: Vince Weaver <vincent.weaver@maine.edu> Link: http://lkml.kernel.org/r/20170118192454.58008-2-davidcc@google.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'include/linux/perf_event.h')
-rw-r--r--include/linux/perf_event.h1
1 files changed, 1 insertions, 0 deletions
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 78ed8105e64d..dfa725723f28 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -788,6 +788,7 @@ struct perf_cpu_context {
struct pmu *unique_pmu;
#ifdef CONFIG_CGROUP_PERF
struct perf_cgroup *cgrp;
+ struct list_head cgrp_cpuctx_entry;
#endif
struct list_head sched_cb_entry;