Messages in this thread Patch in this message |  | | From | Sebastian Andrzej Siewior <> | Subject | [PATCH 1/2] perf bench futex: cache align the worer struct | Date | Sun, 16 Oct 2016 21:08:02 +0200 |
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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. The 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@linutronix.de> --- 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 8024cd5febd2..d9e5e80bb4d0 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"), -- 2.9.3
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