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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@linutronix.de>
Cc: Davidlohr Bueso <dbueso@suse.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20161016190803.3392-1-bigeasy@linutronix.de
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
hifive-unleashed-5.1
Sebastian Andrzej Siewior 2016-10-16 21:08:02 +02:00 committed by Arnaldo Carvalho de Melo
parent 899735066a
commit 34b753007d
1 changed files with 4 additions and 1 deletions
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5
tools/perf/bench/futex-hash.c
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@ -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"),