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

[Jing Zhang]

在 2023/1/6 下午6:14, John Garry 写道:
> On 05/01/2023 21:13, Ian Rogers wrote:
>>>> 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.
>>>>
>>> Maybe during runtime we could create a pseudo metric/event for SLOT.
>> For Intel we do this by just having a different constant for each
>> architecture. It is fairly easy to add a new "literal", so you could
>> add a #slots in expr__get_literal:
>> https://urldefense.com/v3/__https://git.kernel.org/pub/scm/linux/kernel/git/acme/linux.git/tree/tools/perf/util/expr.c?h=perf*core*n407__;LyM!!ACWV5N9M2RV99hQ!IHcZFuFaLdQDQvVOnHVlbbME2S4aW8GohWUkydlejpi7ifFz61r7RutGXReRt0d88X_vDfkTySCiuD2PqOA$ ; Populating it would be the challenge 😄

Yes! I was thinking the same as you, I found this method from the SMT_on variable in icl_metrics.json, then I
tried it and it worked, so excited!

> 
> Thanks for the pointer. I think that the challenge in populating it really comes down to whether we would really want to make this generic.
> 
> I suppose that for arm64 we could have a method which accesses this PMMIR_EL1 register, while for other archs we could have a weak function which just returns NAN. If other archs want to use this key expr, they can add their own method.
> 

Now I have to use this method, because I just found out that neoverse-n2 has been changed to neoverse-n2-v2,
merging n2 and v2. The slots of n2 are 5, and the slots of v2 are 8. I will release the v6 patch and put the
metric in the sbsa.json file. The metrics in sbsa.json is only applicable to arm64, so even if x86 cannot get
the slots value, there will be no conflict.


> Out of curiosity, do you know if x86 has such a capability to get this slot info from HW?
>