Messages in this thread | | | Date | Thu, 24 Nov 2022 16:51:03 +0000 | Subject | Re: [External] : [RFC PATCH v2 1/6] perf vendor events arm64: Add topdown L1 metrics for neoverse-n2 | From | James Clark <> |
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On 24/11/2022 16:32, Jing Zhang wrote: > > > 在 2022/11/23 下午10:26, James Clark 写道: >> >> >> On 22/11/2022 15:41, Jing Zhang wrote: >>> >>> >>> 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. >> >> Because this would apply to all CPUs rather than just N2, I still think >> it's best to wait for our metrics repo to be published. Otherwise Arm >> will start publishing metrics with names and group names for all future >> CPUs that have different names to the common ones added as part of this >> change. >> >> It's something that we've been working on for quite a while and we've >> taken care to make sure that it applies to future products and is scalable. >> >> It would be easier to add these right now only for N2, and then >> afterwards we can start to look at what is common and could be factored >> out into the top level folder. >> >>> If the topdown metrics are different in other CPUs, we can overwrite the >>> metric expression. >> >> True, but with different group names and metric names and units it could >> get slightly complicated. >> >>> >>> 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)", >>> + } >>> +] >>> >> >> With the auto generation of metrics file I don't really see too much >> benefit of doing it this way. >> >> You also run into the issue where if a platform happens to define all of >> the events required by a metric, will that metric appear automatically, >> even if it's not valid? >> > > Ok, I agree to put the topdown metric in the n2 metric instead of arch_std_event. > There is no unified formula for the topdown metric currently, and the slots of each > CPU may be different. > > After the standard are pubulished in the future, please consider what John said, and > use the general metric as arch_std_event.
Yep that sounds good, will do!
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