Re: [External] : [RFC PATCH v2 1/6] perf vendor events arm64: Add topdown L1 metrics for neoverse-n2

Jing Zhang
2022-11-22T15:41:33Z

在 2022/11/22 下午10:00, James Clark 写道:
>
>
> 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
>

I will create a new sbsa.json file in tools/perf/pmu-events/arch/arm64/
to place metrics that may be common between some CPUs, just like arch_std_event.
If the topdown metrics are different in other CPUs, we can overwrite the
metric expression.

For example:

+++ b/tools/perf/pmu-events/arch/arm64/sbsa.json
@@ -0,0 +1,9 @@
+[
+ {
+ "MetricExpr": "stall_slot_frontend / (slot * cpu_cycles)",
+ "PublicDescription": "Frontend bound L1 topdown metric",
+ "BriefDescription": "Frontend bound L1 topdown metric",
+ "MetricGroup": "TopDownL1",
+ "MetricName": "FRONTEND_BOUND"
+ }
+]

+ 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)",
+ }
+]

In addition, I can also add TLB, Cache, Branch, InstructionMix, PEutilization
and other metric groups into sbsa.json, because they are also applicable to
neoverse-n1. Above metrics are described in the documentation of neoverse-n1:
https://developer.arm.com/documentation/PJDOC-466751330-547673/r4p1/

Thanks,
Jing

>>>
>>> Looking forward to your reply.
>>