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

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Date:	Mon, 22 Jul 2013 21:32:43 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Arnaldo Carvalho de Melo <acme@...radead.org>
Cc:	Hitoshi Mitake <mitake.hitoshi@...il.com>,
	Andi Kleen <andi@...stfloor.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

On Mon, Jul 22, 2013 at 01:00:45PM -0300, Arnaldo Carvalho de Melo wrote:
> Em Sat, Jul 20, 2013 at 12:57:27AM +0900, Hitoshi Mitake escreveu:
> > At Thu, 18 Jul 2013 15:43:18 -0700, Andi Kleen wrote:
> > > 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.
> 
> > > +++ b/tools/perf/bench/mem-memcpy.c
> > > @@ -115,8 +115,10 @@ static void alloc_mem(void **dst, void **src, size_t length)
> > >  	*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.
> 
> I fixed this up, please take a look at:
> 
> https://git.kernel.org/cgit/linux/kernel/git/acme/linux.git/commit/?h=perf/core&id=a198996c7afae0097c67a61851f19863e59697b2
> 
> https://git.kernel.org/cgit/linux/kernel/git/acme/linux.git/log/?h=perf/core

Looks good. Thanks.
-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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