linux-kernel - Re: [PATCH] perf-probe: no need to initialize the entire temporary buffers in synthesize_perf_probe

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Message-ID: <m3pqsnvsbo.fsf@gmail.com>
Date:	Mon, 27 Dec 2010 22:06:35 +0100
From:	Franck Bui-Huu <vagabon.xyz@...il.com>
To:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Cc:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	linux-kernel@...r.kernel.org, 2nddept-manager@....hitachi.co.jp
Subject: Re: [PATCH] perf-probe: no need to initialize the entire temporary buffers in synthesize_perf_probe_point()

Arnaldo Carvalho de Melo <acme@...stprotocols.net> writes:

> Em Fri, Dec 24, 2010 at 01:46:09PM +0900, Masami Hiramatsu escreveu:
>> (2010/12/24 0:27), Franck Bui-Huu wrote:
>> > This patches only put a single null byte at the beginning of each
>> > temporary buffers line[], offs[], file[] instead of filling their
>> > full contents with null bytes.
>
>> Hmm, sorry but NAK it.
>
>> IMHO, with modern chips, the original code has no problem from the
>> viewpoint of memory access (all are cached and no need to access just
>> one byte) nor a bottleneck.
>> I'd rather use '= ""' style initialization for local variables from the
>> viewpoint of readability.
>
> No strong feelings here, not really a fast path, just learned something
> new, I thought that that kind of initialization would be equivalent to
> what Franck proposed, but gcc really uses the most efficient way of
> zeroing the whole string (movq for things like that, and rep stos for
> bigger arrays, etc).
> 

gcc has no other choice than clearing the whole buffers here since it's
how C initialisation works.

Thanks
-- 
		Franck
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