On 11/30/2016 07:37 AM, Marc Zyngier wrote:
> On 30/11/16 11:48, Marc Zyngier wrote:
>> + Shannon
>>
>> On 29/11/16 22:04, Itaru Kitayama wrote:
>>> Hi,
>>>
>>> In a VM (virsh controlled, KVM acceleration enabled) on a recent
>>> kvmarm kernel host, I find I am unable to use perf to obtain
>>> performance statistics for a complex task like kernel build.
>>> (I've verified this is seen with a Fedora 25 VM and host combination
>>> as well)
>>> APM folks CC'ed think this might be caused by a bug in the core PMU
>>> framework code, thus I'd like to have experts opinion on this issue.
>>>
>>> [root@localhost linux]# perf stat -B make
>>> CHK include/config/kernel.release
>>> [ 119.617684] git[1144]: undefined instruction: pc=fffffc000808ff30
>>> [ 119.623040] Code: 51000442 92401042 d51b9ca2 d5033fdf (d53b9d40)
>>> [ 119.627607] Internal error: undefined instruction: 0 [#1] SMP
>>
>> [...]
>>
>> In a VM running mainline hosted on an AMD Seattle box:
>>
>> Performance counter stats for 'make':
>>
>> 1526089.499304 task-clock:u (msec) # 0.932 CPUs utilized
>> 0 context-switches:u # 0.000 K/sec
>> 0 cpu-migrations:u # 0.000 K/sec
>> 29527793 page-faults:u # 0.019 M/sec
>> 2913174122673 cycles:u # 1.909 GHz
>> 2365040892322 instructions:u # 0.81 insn per cycle
>> <not supported> branches:u
>> 32049215378 branch-misses:u # 0.00% of all branches
>>
>> 1637.531444837 seconds time elapsed
>>
>> Running the same host kernel on a Mustang system, the guest explodes
>> in the way you reported. The failing instruction always seems to be
>> an access to pmxevcntr_el0 (I've seen both reads and writes).
>>
>> Funnily enough, it dies if you try any HW event other than cycles
>> ("perf stat -e cycles ls" works, and "perf stat -e instructions ls"
>> explodes). Which would tend to indicate that we're screwing up
>> the counter selection, but I have no proof of that (specially that
>> the Seattle guest is working just as expected).
>
> It turns out that we *don't* inject an undef. It seems to be generated
> locally at EL1.
>
> Still digging.
Just FYI: I saw it on Mustang before. My initial thought was HW related,
but without proof. I am interested to see your findings...
>
> M.
>
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