Re: [External] : [RFC PATCH v2 1/6] perf vendor events arm64: Add topdown L1 metrics for neoverse-n2
From: James Clark
Date: Tue Nov 22 2022 - 09:00:29 EST
On 21/11/2022 17:55, John Garry wrote:
> On 21/11/2022 15:17, Jing Zhang wrote:
>> I'm sorry that I misunderstood the purpose of putting metric as
>> arch_std_event at first,
>> and now it works after the modification over your suggestion.
>>
>> But there are also a few questions:
>>
>> 1. The value of the slot in the topdownL1 is various in different
>> architectures, for example,
>> the slot is 5 on neoverse-n2. If I put topdownL1 metric as
>> arch_std_event, then I need to
>> specify the slot to 5 in n2. I can specify slot values in metric like
>> below, but is there any
>> other concise way to do this?
>>
>> diff --git
>> a/tools/perf/pmu-events/arch/arm64/arm/neoverse-n2/metrics.json
>> b/tools/perf/pmu-events/arch/arm64/arm/neoverse-n2/metrics.json
>> index 8ff1dfe..b473baf 100644
>> --- a/tools/perf/pmu-events/arch/arm64/arm/neoverse-n2/metrics.json
>> +++ b/tools/perf/pmu-events/arch/arm64/arm/neoverse-n2/metrics.json
>> @@ -1,4 +1,23 @@
>> [
>> + {
>> + "MetricExpr": "5",
>> + "PublicDescription": "A pipeline slot represents the
>> hardware resources needed to process one uOp",
>> + "BriefDescription": "A pipeline slot represents the
>> hardware resources needed to process one uOp",
>> + "MetricName": "slot"
>
> Ehhh....I'm not sure if that is a good idea. Ian or anyone else have an
> opinion on this? It is possible to reuse metrics, so it should work, but...
>
> One problem is that "slot" would show up as a metric, which you would
> not want.
>
> Alternatively I was going to suggest that you can overwrite specific std
> arch event attributes. So for example of frontend_bound, you could have:
I would agree with not having this and just hard coding the 5 wherever
it's needed. Once we have a few different sets of metrics in place maybe
we can start to look at deduplication, but for now I don't see the value.
>
> + b/tools/perf/pmu-events/arch/arm64/arm/neoverse-n2/metrics.json
> @@ -0,0 +1,30 @@
> [
> {
> "ArchStdEvent": "FRONTEND_BOUND",
> "MetricExpr": "(stall_slot_frontend - cpu_cycles) / (5 *
> cpu_cycles)",
> },
>
>> + }
>> + {
>> + "ArchStdEvent": "FRONTEND_BOUND"
>> + },
>> + {
>> + "ArchStdEvent": "BACKEND_BOUND"
>> + },
>> + {
>> + "ArchStdEvent": "WASTED"
>> + },
>> + {
>> + "ArchStdEvent": "RETIRING"
>> + },
>>
>>
>> 2. Should I add the topdownL1 metric to
>> tools/perf/pmu-event/recommended.json,
>> or create a new json file to place the general metric?
>
> It would not belong in recommended.json as that is specifically for
> arch-recommended events. It would really just depend on where the value
> comes from, i.e. arm arm or sbsa.
>
For what we're going to publish shortly we'll be generating a
metrics.json file for each CPU. It will be autogenerated so I don't
think duplication will be an issue and I'm expecting that there will be
differences in the topdown metrics between CPUs anyway. So I would also
vote to not put it in recommended.json
>>
>> Looking forward to your reply.
>