On 06/03/15 10:36, Peter Zijlstra wrote:
> On Wed, Jun 03, 2015 at 10:03:48AM +0200, Imre Palik wrote:
>> From: "Palik, Imre" <im...@amazon.de>
>>
>> perf doesn't seem to honor the number of fixed counters specified by cpuid
>> leaf 0xa. It always assume that intel CPUs have at least 3 fixed counters.
>>
>> So if some of the fixed counters are masked out by the hypervisor, it still
>> tries to check/set them. This is good for testing the masking code in the
>> hypervisor, but not so nice otherwise.
>>
>> This patch makes perf pehave somewhat nicer when the number of fixed
>> counters is less than three.
>
>> @@ -3042,13 +3042,6 @@ __init int intel_pmu_init(void)
>>
>> x86_pmu.max_pebs_events = min_t(unsigned, MAX_PEBS_EVENTS,
>> x86_pmu.num_counters);
>>
>> - /*
>> - * Quirk: v2 perfmon does not report fixed-purpose events, so
>> - * assume at least 3 events:
>> - */
>> - if (version > 1)
>> - x86_pmu.num_counters_fixed =
>> max((int)edx.split.num_counters_fixed, 3);
>> -
>> if (boot_cpu_has(X86_FEATURE_PDCM)) {
>> u64 capabilities;
>
> So the problem is that there is real hardware out there that gets the
> CPUID stuff wrong, and this patch penalizes that by then not using the
> fixed counters.
I haven't thought about this. Thanks.
> Further, the Intel Arch PerfMon v2 spec actually specifies there to be 3
> fixed function counters.
>
> So anything that says it is v2+ and does not have the 3, is non
> compliant.
>
> I would suggest you go fix your hypervisor.
If I set up the hypervisor to advertise Arch PerfMon v1 (0 fixed counters),
then without my patch, perf still tries to use fixed counters. So something
is clearly broken here.
> Lacking that option; you could probe the MSRs to see if they're really
> there using wrmsr_safe() or something like that -- see
> check_hw_exists().
I'll send something along these lines soon.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
