Re: [PATCHv6 0/3] arm64: perf: Add support for ARMv8.5-PMU 64-bit counters

[Mark Rutland <mark.rutland@arm.com>]

On Mon, Mar 02, 2020 at 06:17:49PM +0000, Mark Rutland wrote:
> This is a respin of Andrew Murray's series to enable support for 64-bit
> counters as introduced in ARMv8.5.
> 
> I've given this a spin on (ARMv8.2) hardware, to test that there are no
> regressions, but I have not had the chance to test in an ARMv8.5 model (which I
> beleive Andrew had previously tested).

Bad news; this is broken. :(

While perf-stat works as expected, perf-record doesn't get samples for
any of the programmable counters.

In ARMv8.4 mode I can do:

| / # perf record -a -c 1 -e armv8_pmuv3/inst_retired/ true
| [ perf record: Woken up 1 times to write data ]
| [ perf record: Captured and wrote 0.023 MB perf.data (367 samples) ]
| / # perf record -a -c 1 -e armv8_pmuv3/inst_retired,long/ true
| [ perf record: Woken up 1 times to write data ]
| [ perf record: Captured and wrote 0.022 MB perf.data (353 samples) ]

... so regular 32-bit and chained events work correctly.

But in ARMv8.5 mode I get no samples in either case:

| / # perf record -a -c 1 -e armv8_pmuv3/inst_retired/ true
| [ perf record: Woken up 1 times to write data ]
| [ perf record: Captured and wrote 0.008 MB perf.data ]
| / # perf report | grep samples
| Error:
| The perf.data file has no samples!
| / # perf record -a -c 1 -e armv8_pmuv3/inst_retired,long/ true
| [ perf record: Woken up 1 times to write data ]
| [ perf record: Captured and wrote 0.008 MB perf.data ]
| / # perf report | grep samples
| Error:
| The perf.data file has no samples!

I'll have to trace the driver to see what's going on. I suspect we've
missed some bias handling, but it's possible that this is a model bug.

Thanks,
Mark.
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