Messages in this thread | | | From | "Kirill A. Shutemov" <> | Subject | RE: [PATCH] perf, tools, bench: Fix memcpy benchmark for large sizes | Date | Mon, 15 Jul 2013 11:15:32 +0300 (EEST) |
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Andi Kleen wrote: > From: Andi Kleen <ak@linux.intel.com> > > glibc calloc() 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. > > Cc: h.mitake@gmail.com > Cc: kirill.shutemov@linux.intel.com > Signed-off-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> --- > tools/perf/bench/mem-memcpy.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/tools/perf/bench/mem-memcpy.c b/tools/perf/bench/mem-memcpy.c > index 93c83e3..690f75f 100644 > --- a/tools/perf/bench/mem-memcpy.c > +++ b/tools/perf/bench/mem-memcpy.c > @@ -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) > -- > 1.8.1.4
-- Kirill A. Shutemov
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