linux-kernel - Re: [BUG] perf_event: inst_retired:any_p:c=16:i=1 is not equivalent to cpu_clk_unhalted:thread

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Message-ID: <1295375793.30950.1056.camel@laptop>
Date:	Tue, 18 Jan 2011 19:36:33 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, mingo@...e.hu,
	Lin Ming <ming.m.lin@...el.com>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [BUG] perf_event: inst_retired:any_p:c=16:i=1 is not
 equivalent to cpu_clk_unhalted:thread_p

On Tue, 2011-01-18 at 19:05 +0100, Stephane Eranian wrote:
> Peter,
> 
> commit 7639dae0ca11038286bbbcda05f2bef601c1eb8d
> Author: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Date:   Tue Dec 14 21:26:40 2010 +0100
> 
>     perf, x86: Provide a PEBS capable cycle event
> 
> 
> 
> Even with the transformation cmask=16:invert=1, you are not quite
> counting the same thing.
> 
> inst_retired:any_p:c=16:i=1  is different from cpu_clk_unhalted:thread_p
> 
> Simply because, I think, this form of inst_retired counts in HALTED state.

Drad it does indeed:

# perf stat -a -e cycles:p -e cycles sleep 1

 Performance counter stats for 'sleep 1':

        61,634,870 cycles                  
        26,703,249 cycles                  

        1.000860820  seconds time elapsed


> This automatic transformation would be "okay" in per-thread mode, but
> not in system-wide mode. It should not be done under the cover. I would
> rather have this option at the user level.

Agreed, since its not identical it had best be done in userspace, too
bad :/ I'll revert this patch.
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