On 2019-08-06 9:52 pm, Vasily Khoruzhick wrote:

On Tue, Aug 6, 2019 at 1:19 PM Harald Geyer [off-list ref] wrote:

quoted

Vasily Khoruzhick writes:

quoted

On Tue, Aug 6, 2019 at 7:35 AM Robin Murphy [off-list ref] wrote:

quoted

On 06/08/2019 15:01, Vasily Khoruzhick wrote:

quoted

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.

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel