linux-kernel - Re: perf failed with kernel 2.6.35-rc

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Date:	Wed, 14 Jul 2010 08:49:52 +0800
From:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	LKML <linux-kernel@...r.kernel.org>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: perf failed with kernel 2.6.35-rc

On Tue, 2010-07-13 at 10:50 +0200, Ingo Molnar wrote:
> * Zhang, Yanmin <yanmin_zhang@...ux.intel.com> wrote:
> 
> > Peter,
> > 
> > perf doesn't work on my Nehalem EX machine.
> > 1) The 1st start of 'perf top' is ok;
> > 2) Kill the 1st perf and restart it. It doesn't work. No data is showed.
> > 
> > I located below commit:
> > commit 1ac62cfff252fb668405ef3398a1fa7f4a0d6d15
> > Author: Peter Zijlstra <peterz@...radead.org>
> > Date:   Fri Mar 26 14:08:44 2010 +0100
> > 
> >     perf, x86: Add Nehelem PMU programming errata workaround
> >     
> >     workaround From: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> >     Date: Fri Mar 26 13:59:41 CET 2010
> >     
> >     Implement the workaround for Intel Errata AAK100 and AAP53.
> >     
> >     Also, remove the Core-i7 name for Nehalem events since there are
> >     also Westmere based i7 chips.
> > 
> > 
> > If I comment out the workaround in function intel_pmu_nhm_enable_all,
> > perf could work.
> > 
> > A quick glance shows:
> > wrmsrl(MSR_CORE_PERF_GLOBAL_CTRL, 0x3);
> > should be:
> > wrmsrl(MSR_CORE_PERF_GLOBAL_CTRL, 0x7);
> 
> > I triggered sysrq to dump PMU registers and found the last bit of
> > global status register is 1. I added a status reset operation like below patch:
> > 
> > --- linux-2.6.35-rc5/arch/x86/kernel/cpu/perf_event_intel.c	2010-07-14 09:38:11.000000000 +0800
> > +++ linux-2.6.35-rc5_fork/arch/x86/kernel/cpu/perf_event_intel.c	2010-07-14 14:41:42.000000000 +0800
> > @@ -505,8 +505,13 @@ static void intel_pmu_nhm_enable_all(int
> >  		wrmsrl(MSR_ARCH_PERFMON_EVENTSEL0 + 1, 0x4300B1);
> >  		wrmsrl(MSR_ARCH_PERFMON_EVENTSEL0 + 2, 0x4300B5);
> >  
> > -		wrmsrl(MSR_CORE_PERF_GLOBAL_CTRL, 0x3);
> > +		wrmsrl(MSR_CORE_PERF_GLOBAL_CTRL, 0x7);
> >  		wrmsrl(MSR_CORE_PERF_GLOBAL_CTRL, 0x0);
> > +		/*
> > +		 * Reset the last 3 bits of global status register in case
> > +		 * previous enabling causes overflows.
> > +		 */
> > +		wrmsrl(MSR_CORE_PERF_GLOBAL_OVF_CTRL, 0x7);
> >  
> >  		for (i = 0; i < 3; i++) {
> >  			struct perf_event *event = cpuc->events[i];
> >
> > 
> > However, it still doesn't work. Current right way is to comment out
> > the workaround.
> 
> Well, how about doing it like this:
> 
> 		wrmsrl(MSR_CORE_PERF_GLOBAL_CTRL, 0x7);
> 		/*
> 		 * Reset the last 3 bits of global status register in case
> 		 * previous enabling causes overflows.
> 		 */
> 		wrmsrl(MSR_CORE_PERF_GLOBAL_OVF_CTRL, 0x7);
>   
>  		for (i = 0; i < 3; i++) {
>   			struct perf_event *event = cpuc->events[i];
> 			...
> 		}
> 
>   		wrmsrl(MSR_CORE_PERF_GLOBAL_CTRL, 0x0);
> 

> I.e. global-mask, overflow-clear, explicit-enable, then global-enable?
Ingo,

wrmsrl(MSR_CORE_PERF_GLOBAL_CTRL, 0x7) is global enable. So it's
global-enable, overflow-clear, explicit-enable, then global-disable?

Yanmin


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