linux-kernel - Re: [PATCH 07/13] perf evlist: Fix creation of cpu map

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Date:	Fri, 04 May 2012 13:05:48 +0900
From:	Namhyung Kim <namhyung.kim@....com>
To:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Cc:	David Ahern <dsahern@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 07/13] perf evlist: Fix creation of cpu map

Hi,

On Wed, 2 May 2012 15:40:33 -0300, Arnaldo Carvalho de Melo wrote:
> Em Fri, Apr 27, 2012 at 09:16:18AM +0900, Namhyung Kim escreveu:
>> So as long as you set perf_event_paranoid to -1 or run perf test as
>> root, you cannot see the failure.
>
> Ok, as root try 'perf top', here I get, with this patch:
>
> [root@...dy ~]# perf top --stdio
> Warning:
> The sys_perf_event_open() syscall returned with 22 (Invalid argument).
> /bin/dmesg may provide additional information.
> No CONFIG_PERF_EVENTS=y kernel support configured?
> [root@...dy ~]#
>
> Skipping this one, will look again later.
>
> - Arnaldo

Sorry. It is because perf top depends on an undefined behaviour that
if neither target nor command line argument was specified it'd open
events for all online cpus. In contrast, perf record and perf stat will
show the help message in this case.

This patch makes it clear that we have to prepare a sane target
configuration before opening a perf event fd. So I think we should fix
perf top to set top.target.system_wide to true by default.

Thanks,
Namhyung
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