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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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