Re: [PATCH v5 1/6] perf vendor events arm64: Add topdown L1 metrics for neoverse-n2

[Jing Zhang]

在 2023/1/5 上午1:26, John Garry 写道:
> On 04/01/2023 05:05, Jing Zhang wrote:
>>
>>
>> 在 2023/1/3 下午7:52, John Garry 写道:
>>> On 03/01/2023 11:39, Jing Zhang wrote:
>>>> The formula of topdown L1 on neoverse-n2 is from ARM sbsa7.0 platform
>>>> design document [0], D37-38.
>>>
>>> I think that I mentioned this before - if the these metrics are coming from an sbsa doc, then they are standard. As such, we can make them "arch std events" and put them in a common json such as sbsa.json, so that other cores may reuse.
>>>
>>> You don't strictly have to do do this now, but it would be better.
>>>
>>
>> Hi John,
> 
> Hi Jing,
> 
>>
>> I would really like to do this, but as discussed earlier, slot is different on each architectures.
>> If I do not specify the value of the slot in sbsa.json, then in the json file of n2/v1, I need to
>> overwrite each topdown "MetricExpr". In other words, the metrics placed in the sbsa.json file only
>> reuse "BriefDescription", "MetricGroup" and "ScaleUnit". So I'm not sure if it's acceptable?
> 
> I don't see a lot of value in that really.
> 
> However, for this value of slot, isn't this discoverable from a system register per core? Quoting the sbsa: "The IMPLEMENTATION DEFINED constant SLOTS is discoverable from the system register PMMIR_EL1.SLOTS." Did you consider how this could be used?
> 


This may be a feasible idea. The value of slots comes from the register PMMIR_EL1, which I can read in
/sys/bus/event_source/device/armv8_pmuv3_*/caps/slots. But how do I replace the slots in MetricExpr with the
read slots values? Currently I understand that parameters in metricExpr only support events and constants.