Messages in this thread | | | Date | Mon, 16 May 2022 19:05:27 +0100 | Subject | Re: [PATCH 00/20] perf vendors events arm64: Multiple Arm CPUs | From | Nick Forrington <> |
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On 15/05/2022 23:03, Ian Rogers wrote: > On Thu, May 12, 2022 at 8:53 AM John Garry <john.garry@huawei.com> wrote: > > Generally this looks ok: > > Reviewed-by: John Garry <john.garry@huawei.com> > > If you are feeling particularly helpful then you can add support for any > events missing to pre-existing core support, like a57-a72. > > I'll raise John's "ok" and say this looks great! :-D Some thoughts:
Thanks Ian!
> The mapfile.csv cpuid values don't directly align with: > https://github.com/ARM-software/data/blob/master/cpus.json > but this definitely looks deliberate.
Correct - they use different formats.
mapfile.csv uses the MIDR format
https://developer.arm.com/documentation/100442/0100/register-descriptions/aarch64-system-registers/midr-el1--main-id-register--el1
The cpus.json "cpuid" is the implementer and part number from the MIDR (the other fields are always fixed in mapfile.csv) > The new events lack the PMU "Unit" value. The current perf json is > pretty free form and leads to problems if two PMUs are present. > Context is here: > https://lore.kernel.org/lkml/CAP-5=fWRRZsyJZ-gky-FOFz79zW_3r78d_0APpj5sf66HqTpLw@mail.gmail.com/ > > My idea to rationalize this is to mirror what is already done in > sysfs, that is the event data is specific to a PMU. As a lot of "Unit" > values are missing from events on x86 a reasonable guess if the "Unit" > is missing is to use "cpu". Poking a Google Pixel 4a, I see that all > PMU data is in "armv8_pmuv3". So for ARM I could guess this is always > the case, ie all events should belong to armv8_pmuv3. This may not be > right and could lead to confusion like an event BR_COND_MIS_PRED > having an alias of "armv8_pmuv3/BR_COND_MIS_PRED/" but it really > should have some other PMU name in there. I just raise this in case > there is a fix for this we could incorporate into this patch series, > maybe "armv8_pmuv3" is always the PMU and my life is easy.
My understanding is that all JSON events under arm64/arm apply to the CPU PMU, although there could be 2 (or more) armv8_pmuv3 devices in a herterogeneous system (armv8_pmuv3_0, armv8_pmuv3_1, ...) - each with different events.
So I don't think static "Unit" data would be helpful, but it should be possible to map JSON events to appropriate CPUs with existing data.
e.g. /sys/bus/event_source/devices/armv8_pmuv3_0/cpus shows the CPUs associated with a PMU device, and each CPU can be mapped to JSON events via the MIDR (as is done already)
Thanks, Nick
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