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    SubjectRe: perf failed with kernel 2.6.35-rc
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    What about running simpler commands like perf stat?


    On Wed, Jul 14, 2010 at 2:13 AM, Zhang, Yanmin
    <yanmin_zhang@linux.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@linux.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@infradead.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@chello.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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