linux-kernel - Re: [PATCH -tip/perf/core] perf, x86: P4 PMU

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Date:	Wed, 06 Jul 2011 13:38:41 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Cyrill Gorcunov <gorcunov@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Don Zickus <dzickus@...hat.com>,
	Stephane Eranian <eranian@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -tip/perf/core] perf, x86: P4 PMU - Drop redundant
 WARN_ON_ONCE

On Wed, 2011-07-06 at 21:24 +0400, Cyrill Gorcunov wrote:
> This WARN_ON_ONCE triggers a false alarm on SMP because
> nmi-watchdog uses a single global 'wd_hw_attr' variable
> to serve perf event attributes and once p4_hw_watchdog_set_attr
> has modified it subsequent calls on the rest cpus trigger
> the warning.
> 
> It is safe to simply drop it since we know the caller may
> pass already altered type and config.
> 
> Repoted-by: Steven Rostedt <rostedt@...dmis.org>

Repoted? Hmm, maybe symbolically I put this code in a different pot.

Reported-and-tested-by: Steven Rostedt <rostedt@...dmis.org>

-- Steve

> Signed-off-by: Cyrill Gorcunov <gorcunov@...nvz.org>
> ---
>  arch/x86/kernel/cpu/perf_event_p4.c |    3 ---
>  1 file changed, 3 deletions(-)
> 
> Index: linux-2.6.git/arch/x86/kernel/cpu/perf_event_p4.c
> ===================================================================
> --- linux-2.6.git.orig/arch/x86/kernel/cpu/perf_event_p4.c
> +++ linux-2.6.git/arch/x86/kernel/cpu/perf_event_p4.c
> @@ -726,9 +726,6 @@ static void p4_hw_watchdog_set_attr(stru
>  	 * that named "non-sleeping" ticks as recommended
>  	 * by Intel SDM Vol3b.
>  	 */
> -	WARN_ON_ONCE(wd_attr->type	!= PERF_TYPE_HARDWARE ||
> -		     wd_attr->config	!= PERF_COUNT_HW_CPU_CYCLES);
> -
>  	wd_attr->type	= PERF_TYPE_RAW;
>  	wd_attr->config	=
>  		p4_config_pack_escr(P4_ESCR_EVENT(P4_EVENT_EXECUTION_EVENT)		|


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