Commit a198996c authored Jul 18, 2013 by Andi Kleen Committed by Arnaldo Carvalho de Melo Jul 22, 2013

perf bench: Fix memcpy benchmark for large sizes



The glibc calloc() function has an optimization to not explicitely
memset() very large calloc allocations that just came from mmap(),
because they are known to be zero.

This could result in the perf memcpy benchmark reading only from
the zero page, which gives unrealistic results.

Always call memset explicitly on the source area to avoid this problem.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Cc: Hitoshi Mitake <h.mitake@gmail.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Link: http://lkml.kernel.org/n/tip-pzz2qrdq9eymxda0y8yxdn33@git.kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

parent 2b821cce

tools/perf/bench/mem-memcpy.c

+2 −0

Original line number	Diff line number	Diff line
		@@ -117,6 +117,8 @@ static void alloc_mem(void dst, void src, size_t length)
		*src = zalloc(length);
		if (!*src)
		die("memory allocation failed - maybe length is too large?\n");
		/* Make sure to always replace the zero pages even if MMAP_THRESH is crossed */
		memset(*src, 0, length);
		}

		static u64 do_memcpy_cycle(memcpy_t fn, size_t len, bool prefault)