linux-kernel - Re: [PATCH] perf, tools, bench: Fix memcpy benchmark for large sizes v2

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Date:	Sat, 20 Jul 2013 00:57:27 +0900
From:	Hitoshi Mitake <mitake.hitoshi@...il.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	acme@...radead.org, linux-kernel@...r.kernel.org,
	Andi Kleen <ak@...ux.intel.com>, h.mitake@...il.com,
	kirill.shutemov@...ux.intel.com
Subject: Re: [PATCH] perf, tools, bench: Fix memcpy benchmark for large sizes v2

At Thu, 18 Jul 2013 15:43:18 -0700,
Andi Kleen wrote:
> 
> From: Andi Kleen <ak@...ux.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@...il.com
> Cc: kirill.shutemov@...ux.intel.com
> v2: Actually memset the right area and also fix the NULL check before.
> Signed-off-by: Andi Kleen <ak@...ux.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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