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

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Date:	Wed, 14 Jul 2010 02:36:21 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: perf failed with kernel 2.6.35-rc

What about running simpler commands like perf stat?


On Wed, Jul 14, 2010 at 2:13 AM, Zhang, Yanmin
<yanmin_zhang@...ux.intel.com> wrote:
> On Tue, 2010-07-13 at 17:16 +0200, Stephane Eranian wrote:
>> On Tue, Jul 13, 2010 at 10:14 AM, 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:
>> >
>> What do you call the last bit? bit0 or bit63?
> Sorry for confusing you. It's bit0, mapping to PERFMON_EVENTSEL0.
>
>>
>> > --- 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.
>> > +                */
>>
>> The workaround cannot cause on overflow because the associated counters
>> won't count anything given their umask value is 0 (which does not correspond
>> to anything for event 0xB1, event 0xB5 is undocumented). This is for the events
>> described in table A.2. If NHM-EX has a different definition for 0xB1, 0xB5,
>> then that's another story.
> I found the status bit is set by triggering sysrq to dump PMU registers.
>
> If I start perf by gdb, sometimes, perf could work. I found one processor's 1st status
> register is equal to 0 while other processors' are 1. If just starting perf, all 1st
> status registers are equal to 1.
>
>>
>>
>> > +               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.
>
>
>
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