linux-kernel - Re: [PATCH -tip] perf_counter/x86: Correct some event and umask values for Intel processors

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Message-ID: <20090612081526.GB2286@ywang-moblin2.bj.intel.com>
Date:	Fri, 12 Jun 2009 16:15:26 +0800
From:	Yong Wang <yong.y.wang@...ux.intel.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [PATCH -tip] perf_counter/x86: Correct some event and umask
	values for Intel processors

On Wed, Jun 10, 2009 at 12:42:42PM +0200, Ingo Molnar wrote:
> 
> * Yong Wang <yong.y.wang@...ux.intel.com> wrote:
> 
> > On Tue, Jun 09, 2009 at 04:16:21PM +0200, Ingo Molnar wrote:
> > > 
> > > * Yong Wang <yong.y.wang@...ux.intel.com> wrote:
> > > 
> > > > Correct some event and UMASK values according to Intel SDM.
> > > 
> > > Very nice, thanks!
> > > 
> > > were you able to test the Atom ones by any chance?
> > > 
> > 
> > You bet I was as I'm working on Moblin ;-) [...]
> 
> Heh :-)
> 
> > [...] However, some work while some do not. I'll take a look at 
> > the problematic ones. With the previous event and umask values, 
> > the pmc does not count at all for some events, like l1d-write-ops.
> 
> Interesting. I had a good look at the Atom details in the docs but 
> couldnt find anything suspicious. There's various umask level 
> extensions (sometimes cflags level ones) like whether to measure the 
> core or the thread, but the defaults (zero) seem to have OK 
> semantics for most of the events.
> 
> Btw., when mapping out event tables there's one little trick i used 
> to 'scan' an event, using 'perf stat' and raw event numbers:
> 
>   for ((i=0;i<256;i++)); do                                    \
>     perf stat -e $(printf "r%02x%02x\n" $i 0xc0) true 2>&1 |   \
>       grep -w raw | grep -vw 0;                                \
>   done
> 
> This scans all 256 umask values for the main event code of 0xc0, and 
> displays the umask values where the counter show some activity.
> 
> ( if it's some rare event then you might want to run something else 
>   that excercises that event, not /bin/true. )
> 

Just took a look at the problematics ones and found that the fixed
function PMCs do not work on current Atom processors. I tested on 3 Atom
netbooks and the results are the same. Just sent a quirk patch for that.

-Yong
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