Re: [PATCH] arm64: dts: allwinner: a64: Drop PMU node

Robin Murphy
2019-08-06T21:14:47Z

On 2019-08-06 9:52 pm, Vasily Khoruzhick wrote:
> On Tue, Aug 6, 2019 at 1:19 PM Harald Geyer <harald@ccbib.org> wrote:
>>
>> Vasily Khoruzhick writes:
>>> On Tue, Aug 6, 2019 at 7:35 AM Robin Murphy <robin.murphy@arm.com> wrote:
>>>>
>>>> On 06/08/2019 15:01, Vasily Khoruzhick wrote:
>>>>> Looks like PMU in A64 is broken, it generates no interrupts at all and
>>>>> as result 'perf top' shows no events.
>>>>
>>>> Does something like 'perf stat sleep 1' at least count cycles correctly?
>>>> It could well just be that the interrupt numbers are wrong...
>>>
>>> Looks like it does, at least result looks plausible:
>>
>> I'm using perf stat regularly (cache benchmarks) and it works fine.
>>
>> Unfortunately I wasn't aware that perf stat is a poor test for
>> the interrupts part of the node, when I added it. So I'm not too
>> surprised I got it wrong.
>>
>> However, it would be unfortunate if the node got removed completely,
>> because perf stat would not work anymore. Maybe we can only remove
>> the interrupts or just fix them even if the HW doesn't work?
>
> I'm not familiar with PMU driver. Is it possible to get it working
> without interrupts?

Yup - you get a grumpy message from the driver, it will refuse sampling
events (the ones which weren't working anyway), and if you measure
anything for long enough that a counter overflows you'll get wonky
results. But for counting hardware events over relatively short periods
it'll still do the job.

Robin.