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

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Date:	Fri, 24 Dec 2010 13:46:09 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Franck Bui-Huu <vagabon.xyz@...il.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()

(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.

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.

Anyway, thank you for looking into the code :-)

Thanks,

> 
> Signed-off-by: Franck Bui-Huu <fbuihuu@...il.com>
> ---
>  tools/perf/util/probe-event.c |    4 +++-
>  1 files changed, 3 insertions(+), 1 deletions(-)
> 
> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
> index adc2620..e453f13 100644
> --- a/tools/perf/util/probe-event.c
> +++ b/tools/perf/util/probe-event.c
> @@ -1058,9 +1058,11 @@ error:
>  static char *synthesize_perf_probe_point(struct perf_probe_point *pp)
>  {
>  	char *buf, *tmp;
> -	char offs[32] = "", line[32] = "", file[32] = "";
> +	char offs[32], line[32], file[32];
>  	int ret, len;
>  
> +	offs[0] = line[0] = file[0] = '\0';
> +
>  	buf = zalloc(MAX_CMDLEN);
>  	if (buf == NULL) {
>  		ret = -ENOMEM;


-- 
Masami HIRAMATSU
2nd Dept. Linux Technology Center
Hitachi, Ltd., Systems Development Laboratory
E-mail: masami.hiramatsu.pt@...achi.com
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