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    SubjectRe: 2.6.31-rc5 regression: x86 MCE malfunction on Thinkpad T42p

    * Johannes Stezenbach <js@sig21.net> wrote:

    > On Mon, Aug 10, 2009 at 10:14:06PM +0200, Ingo Molnar wrote:
    > > * Johannes Stezenbach <js@sig21.net> wrote:
    > > >
    > > > # ./perf stat true
    > > >
    > > > Performance counter stats for 'true':
    > > >
    > > > 0.985808 task-clock-msecs # 0.779 CPUs
    > > > 0 context-switches # 0.000 M/sec
    > > > 0 CPU-migrations # 0.000 M/sec
    > > > 110 page-faults # 0.112 M/sec
    > > > 583873 cycles # 592.279 M/sec
    > > > 500937 instructions # 0.858 IPC
    > > > <not counted> cache-references
    > > > <not counted> cache-misses
    > > >
    > > > 0.001265524 seconds time elapsed
    > >
    > > That looks almost normal - except for cache-references and
    > > cache-misses that is not counted. Could you send the /proc/cpuinfo
    > > info please?
    >
    > # cat /proc/cpuinfo
    > processor : 0
    > vendor_id : GenuineIntel
    > cpu family : 6
    > model : 13
    > model name : Intel(R) Pentium(R) M processor 1.80GHz

    ah, yes. There's no cache-references/misses, because in
    arch/x86/kernel/cpu/perf_counter.c we have two zero entries:

    static const u64 p6_perfmon_event_map[] =
    {
    [PERF_COUNT_HW_CPU_CYCLES] = 0x0079,
    [PERF_COUNT_HW_INSTRUCTIONS] = 0x00c0,
    [PERF_COUNT_HW_CACHE_REFERENCES] = 0x0000, <----------
    [PERF_COUNT_HW_CACHE_MISSES] = 0x0000, <----------
    [PERF_COUNT_HW_BRANCH_INSTRUCTIONS] = 0x00c4,
    [PERF_COUNT_HW_BRANCH_MISSES] = 0x00c5,
    [PERF_COUNT_HW_BUS_CYCLES] = 0x0062,
    };

    i.e. PERF_COUNT_HW_CACHE_REFERENCES and PERF_COUNT_HW_CACHE_MISSES
    is not filled in yet.

    Could you try something like:

    perf stat -e r0f2e true

    (0x2e: L2 requests, 0x0f: all units)

    if i checked the docs right that counter would give us L2 cache
    stats - does it display non-zero values?

    > stepping : 6
    > cpu MHz : 600.000
    > cache size : 2048 KB
    > fdiv_bug : no
    > hlt_bug : no
    > f00f_bug : no
    > coma_bug : no
    > fpu : yes
    > fpu_exception : yes
    > cpuid level : 2
    > wp : yes
    > flags : fpu vme de pse tsc msr mce cx8 apic sep mtrr pge mca cmov clflush dts acpi mmx fxsr sse sse2 ss tm pbe bts est tm2
    > bogomips : 1196.15
    > clflush size : 64
    > power management:
    >
    >
    > > The warning is probably harmless - oprofile sampling still works
    > > fine, right?
    >
    > I haven't done much testing so far, but so far it looks promising.
    >
    > Could the warning be caused by the cpufreq ondemand governor? ISTR
    > that one should switch to the performance governor before doing
    > any profiling, but I forgot for this test.

    there might be a connection - it could in theory cause sched_clock()
    transients and confuse the ring-buffer time-stamping.

    Ingo


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