At Mon, 15 Jul 2013 11:15:32 +0300 (EEST),
Kirill A. Shutemov wrote:
>
> Andi Kleen wrote:
> > From: Andi Kleen <a...@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.mit...@gmail.com
> > Cc: kirill.shute...@linux.intel.com
> > Signed-off-by: Andi Kleen <a...@linux.intel.com>
>
> Acked-by: Kirill A. Shutemov <kirill.shute...@linux.intel.com>
Thanks for this fix, Andi.
Acked-by: Hitoshi Mitake <mitake.hito...@lab.ntt.co.jp>
>
> > ---
> > 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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