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

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Message-ID: <m3tyhzvsjr.fsf@gmail.com>
Date:	Mon, 27 Dec 2010 22:01:44 +0100
From:	Franck Bui-Huu <vagabon.xyz@...il.com>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	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()

Masami Hiramatsu <masami.hiramatsu.pt@...achi.com> writes:

> (2010/12/24 0:27), Franck Bui-Huu wrote:
>> From: Franck Bui-Huu <fbuihuu@...il.com>
>> 
>> 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.
>

No problem :)

>
> 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'm not sure to understand this.

But my point is that you're clearing the whole buffers with 0 although
you just need to initialize them with the null string (a single null
byte at the beginning).

So you're doing useless memory accesses (cached or not).

I agree with you that it won't make any speed improvements though, but
it was just clearer for me, since what you want are null strings and not
a char arrays fill with 0.

Thanks.
-- 
		Franck
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