At Thu, 18 Jul 2013 15:43:18 -0700,
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
> v2: Actually memset the right area and also fix the NULL check before.
> Signed-off-by: Andi Kleen <a...@linux.intel.com>
> ---
> tools/perf/bench/mem-memcpy.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/tools/perf/bench/mem-memcpy.c b/tools/perf/bench/mem-memcpy.c
> index 93c83e3..0887b46 100644
> --- a/tools/perf/bench/mem-memcpy.c
> +++ b/tools/perf/bench/mem-memcpy.c
> @@ -115,8 +115,10 @@ static void alloc_mem(void **dst, void **src, size_t
> length)
> die("memory allocation failed - maybe length is too large?\n");
>
> *src = zalloc(length);
> - if (!src)
> + if (!*src)
In the latest mem-memcpy.c, this if (!src) is already fixed as if
(!*src). This modification makes applying fail.
Thanks,
Hitoshi
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