Re: [PATCH 1/5] perf metricgroup: Support printing metrics for arm64

[John Garry <john.garry@huawei.com>]

On 06/03/2021 19:34, Jiri Olsa wrote:
> On Fri, Mar 05, 2021 at 11:06:58AM +0000, John Garry wrote:
>> Hi Jirka,
>>
>>>> -	struct pmu_events_map *map = perf_pmu__find_map(NULL);
>>>> +	struct pmu_events_map *map = find_cpumap();
>>> so this is just for arm at the moment right?
>>>
>> Yes - but to be more accurate, arm64.
>>
>> At the moment, from the archs which use pmu-events, only arm64 and nds32
>> have versions of get_cpuid_str() which require a non-NULL pmu argument.
>>
>> But then apparently nds32 only supports a single CPU, so this issue of
>> heterogeneous CPUs should not be a concern there:)
>>
>>> could we rather make this arch specific code, so we don't need
>>> to do the scanning on archs where this is not needed?
>>>
>>> like marking perf_pmu__find_map as __weak and add arm specific
>>> version?
>> Well I was thinking that this code should not be in metricgroup.c anyway.
>>
>> So there is code which is common in current perf_pmu__find_map() for all
>> archs.
>>
>> I could factor that out into a common function, below. Just a bit worried
>> about perf_pmu__find_map() and perf_pmu__find_pmu_map() being confused.
> right, so perf_pmu__find_map does not take perf_pmu as argument
> anymore, so the prefix does not fit, how about pmu_events_map__find ?

I think it could be ok.

But now I am slightly concerned that we don't put anything like this in 
arch/arm64, based on this earlier discussion on close topic:

https://lore.kernel.org/lkml/20190719075450.xcm4i4a5sfaxlfap@willie-the-truck/

Hi Will, Mark,

Do you have any objection to add arm64 specific code here?

So what I had originally in this patch was to iterate PMUs  in common 
code and find the CPU PMU and use that to match CPU metrics, as long as 
it's not a heterogeneous system.

Now the suggestion was to move that into arch specific code, as it's not 
needed for all archs.

Thanks,
John