linux-kernel - Re: [PATCH v2] perf bench: fix order of arguments to memcpy_alloc

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Date:	Thu, 19 Feb 2015 01:31:11 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Bruce Merry <bmerry@....ac.za>
Cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Jiri Olsa <jolsa@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...radead.org>
Subject: Re: [PATCH v2] perf bench: fix order of arguments to memcpy_alloc_mem


* Bruce Merry <bmerry@....ac.za> wrote:

> This was causing the destination instead of the source to be filled.
> As a result, the source was typically all mapped to one zero page,
> and hence very cacheable.
> 
> Signed-off-by: Bruce Merry <bmerry@....ac.za>
> ---
>  tools/perf/bench/mem-memcpy.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/perf/bench/mem-memcpy.c b/tools/perf/bench/mem-memcpy.c
> index 6c14afe..db1d3a2 100644
> --- a/tools/perf/bench/mem-memcpy.c
> +++ b/tools/perf/bench/mem-memcpy.c
> @@ -289,7 +289,7 @@ static u64 do_memcpy_cycle(const struct routine *r, size_t len, bool prefault)
>  	memcpy_t fn = r->fn.memcpy;
>  	int i;
>  
> -	memcpy_alloc_mem(&src, &dst, len);
> +	memcpy_alloc_mem(&dst, &src, len);
>  
>  	if (prefault)
>  		fn(dst, src, len);
> @@ -312,7 +312,7 @@ static double do_memcpy_gettimeofday(const struct routine *r, size_t len,
>  	void *src = NULL, *dst = NULL;
>  	int i;
>  
> -	memcpy_alloc_mem(&src, &dst, len);
> +	memcpy_alloc_mem(&dst, &src, len);
>  
>  	if (prefault)
>  		fn(dst, src, len);

Acked-by: Ingo Molnar <mingo@...nel.org>

Thanks,

	Ingo
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