linux-kernel - Re: [PATCH 03/11] perf tool: Use PERF_EVENT_IOC

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Message-ID: <87ehkrj5wb.fsf@sejong.aot.lge.com>
Date:	Mon, 22 Oct 2012 16:57:24 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>, Paul Mackerras <paulus@...ba.org>,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH 03/11] perf tool: Use PERF_EVENT_IOC_ID perf ioctl to read event id

Hi,

Just a minor nitpicking..


On Sat, 20 Oct 2012 16:33:11 +0200, Jiri Olsa wrote:
> Changing the way we retrieve the event ID. Instead of parsing out
> the ID out of the read data, using the PERF_EVENT_IOC_ID ioctl.
>
> Keeping the old way in place to support kernels without
> PERF_EVENT_IOC_ID ioctl support.
[snip]
> +	} else if (errno)
> +		return -1;

Is this check really needed?  I think that returning non-zero from the
ioctl always sets the errno, no?  How about this:

	ret = ioctl(fd, PERF_EVENT_IOC_ID, &id);
	if (!ret)
		goto add;

	if (errno != ENOTTY)
		return -1;

	...

I guess that it'll show you better diff stat. :)

Thanks,
Namhyung

>  
> -	perf_evlist__id_add(evlist, evsel, cpu, thread, read_data[id_idx]);
> + add:
> +	perf_evlist__id_add(evlist, evsel, cpu, thread, id);
>  	return 0;
>  }
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