linux-kernel - Re: [patch] perf

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Date:	Wed, 08 Jul 2009 23:45:29 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Vince Weaver <vince@...ter.net>
Cc:	Ingo Molnar <mingo@...e.hu>, Paul Mackerras <paulus@...ba.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [patch] perf_counter: Add p6 PMU

On Wed, 2009-07-08 at 17:46 -0400, Vince Weaver wrote:
> On Wed, 8 Jul 2009, Peter Zijlstra wrote:
> 
> >   doesn't sound like the right kind of event.. but then, it doesn't
> >   have anything better either.
> 
> Is there a way to specify "invalid event"?  Just setting it to 0 doesn't 
> work, on the Pentium Pro event 0 returns what looks like essentially
> random numbers.

Hmm, bugger. I was assuming writing 0 to the evensel would disable the
counter. Apparently that only works for eventsel1, which would mean we
cannot run counter1 without counter0. That means we'd need to do a
counter swap at times... :/

I think we can extend __hw_perf_counter_init() to return failure when
->event_map() returns 0 or something.

> > 
> >  - s/CORE_/P6_/ for the evntsel masks
> 
> thanks, I missed that.
> 
> > -	int err;
> > -	err = checking_wrmsrl(hwc->config_base + idx,
> > +	(void)checking_wrmsrl(hwc->config_base + idx,
> 
> the patches that do the above seem to be unrelated to p6 support.
> Did they get mixed in somehow?

Yeah, random cleanups..

> The patch as it stands will break non-p6 intel perf counters, as Core2 and 
> atom are also cpu family 6.  The attached patch takes the updated version 
> you sent out, and includes a fix to the detection logic.

Ah, thanks!

> Also the current patch gives the following warning:
>  arch/x86/kernel/cpu/perf_counter.c: In function p6_pmu_disable_counter:
>  arch/x86/kernel/cpu/perf_counter.c:925: warning: right shift count >= width of type

#define checking_wrmsrl(msr, val) wrmsr_safe((msr), (u32)(val),         \
                                             (u32)((val) >> 32))

and I passed in a unsigned long, which on ia32 is well 32 bits :-)

> though I don't see where that actually happens, unless some deep macro 
> magic is going on.
> 
> Patch attached below.  This is my first attempt at kernel development in 
> the modern era, so I have no idea how to do the signed off by if multiple 
> people are involved.  Do I just put then all together?

Yeah, that usually works..

Thanks, I'll have a got at it tomorrow.


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