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

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Message-ID: <20130722160045.GG2157@ghostprotocols.net>
Date:	Mon, 22 Jul 2013 13:00:45 -0300
From:	Arnaldo Carvalho de Melo <acme@...radead.org>
To:	Hitoshi Mitake <mitake.hitoshi@...il.com>
Cc:	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

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

- Arnaldo
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