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.
M.
--
Jazz is not dead. It just smells funny...
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