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Date: Mon, 24 Oct 2016 12:06:24 -0700 From: tip-bot for Sebastian Andrzej Siewior <tipbot@...or.com> To: linux-tip-commits@...r.kernel.org Cc: acme@...hat.com, peterz@...radead.org, tglx@...utronix.de, dbueso@...e.de, hpa@...or.com, mingo@...nel.org, bigeasy@...utronix.de, linux-kernel@...r.kernel.org Subject: [tip:perf/core] perf bench futex: Cache align the worker struct Commit-ID: 34b753007d646482a4125a7095e1d1986d395f95 Gitweb: http://git.kernel.org/tip/34b753007d646482a4125a7095e1d1986d395f95 Author: Sebastian Andrzej Siewior <bigeasy@...utronix.de> AuthorDate: Sun, 16 Oct 2016 21:08:02 +0200 Committer: Arnaldo Carvalho de Melo <acme@...hat.com> CommitDate: Mon, 24 Oct 2016 11:07:45 -0300 perf bench futex: Cache align the worker struct It popped up in perf testing that the worker consumes some amount of CPU. It boils down to the increment of `ops` which causes cache line bouncing between the individual threads. This patch aligns the struct by 256 bytes to ensure that not a cache line is shared among CPUs. 128 byte is the x86 worst case and grep says that L1_CACHE_SHIFT is set to 8 on s390. Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de> Cc: Davidlohr Bueso <dbueso@...e.de> Cc: Peter Zijlstra <peterz@...radead.org> Link: http://lkml.kernel.org/r/20161016190803.3392-1-bigeasy@linutronix.de Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com> --- tools/perf/bench/futex-hash.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/tools/perf/bench/futex-hash.c b/tools/perf/bench/futex-hash.c index 8024cd5..d9e5e80 100644 --- a/tools/perf/bench/futex-hash.c +++ b/tools/perf/bench/futex-hash.c @@ -39,12 +39,15 @@ static unsigned int threads_starting; static struct stats throughput_stats; static pthread_cond_t thread_parent, thread_worker; +#define SMP_CACHE_BYTES 256 +#define __cacheline_aligned __attribute__ ((aligned (SMP_CACHE_BYTES))) + struct worker { int tid; u_int32_t *futex; pthread_t thread; unsigned long ops; -}; +} __cacheline_aligned; static const struct option options[] = { OPT_UINTEGER('t', "threads", &nthreads, "Specify amount of threads"),
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