Messages in this thread |  | | Date | Sun, 4 Dec 2022 15:10:37 +0800 | Subject | Re: [PATCH v3 5/6] perf vendor events arm64: Add PE utilization metrics for neoverse-n2 | From | Jing Zhang <> |
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在 2022/12/3 上午4:05, Ian Rogers 写道: > On Thu, Dec 1, 2022 at 3:08 AM Jing Zhang <renyu.zj@linux.alibaba.com> wrote: >> >> >> >> 在 2022/12/1 上午2:58, Ian Rogers 写道: >>> On Thu, Nov 24, 2022 at 9:15 AM Jing Zhang <renyu.zj@linux.alibaba.com> wrote: >>>> >>>> Add PE utilization related metrics. >>>> >>>> Signed-off-by: Jing Zhang <renyu.zj@linux.alibaba.com> >>>> --- >>>> .../arch/arm64/arm/neoverse-n2/metrics.json | 45 ++++++++++++++++++++++ >>>> 1 file changed, 45 insertions(+) >>>> >>>> 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 23c7d62..7b54819 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 >>>> @@ -189,5 +189,50 @@ >>>> "MetricGroup": "Branch", >>>> "MetricName": "branch_miss_pred_rate", >>>> "ScaleUnit": "100%" >>>> + }, >>>> + { >>>> + "MetricExpr": "instructions / CPU_CYCLES", >>>> + "PublicDescription": "The average number of instructions executed for each cycle.", >>>> + "BriefDescription": "Instructions per cycle", >>>> + "MetricGroup": "PEutilization", >>>> + "MetricName": "ipc" >>>> + }, >>> >>> A related useful metric is percentage of peak, so if the peak IPC is 8 >>> (usually a constant related to the number of functional units) then >>> you can just compute the ratio of IPC with this. >>> >> >> Glad to discuss these with you. >> The peak ipc value of neoverse-n2 is 5. Maybe I should add an ipc_rate metric? >> >>>> + { >>>> + "MetricExpr": "INST_RETIRED / CPU_CYCLES", >>>> + "PublicDescription": "Architecturally executed Instructions Per Cycle (IPC)", >>>> + "BriefDescription": "Architecturally executed Instructions Per Cycle (IPC)", >>> >>> >>> The duplicated descriptions are unnecessary. Drop the public one for >>> consistency with what we do for Intel: >>> https://github.com/intel/perfmon/blob/main/scripts/create_perf_json.py#L299 >>> >> >> Sounds good, will do. >> >>>> + "MetricGroup": "PEutilization", >>>> + "MetricName": "retired_ipc" >>>> + }, >>>> + { >>>> + "MetricExpr": "INST_SPEC / CPU_CYCLES", >>>> + "PublicDescription": "Speculatively executed Instructions Per Cycle (IPC)", >>>> + "BriefDescription": "Speculatively executed Instructions Per Cycle (IPC)", >>>> + "MetricGroup": "PEutilization", >>>> + "MetricName": "spec_ipc" >>>> + }, >>>> + { >>>> + "MetricExpr": "OP_RETIRED / OP_SPEC", >>>> + "PublicDescription": "Fraction of operations retired", >>>> + "BriefDescription": "Fraction of operations retired", >>> >>> Would instructions be clearer than operations here? >>> >> >> operation and instruction are different. OP_RETIRED counts any operation (not instruction) >> that has been architecturally executed, For example, speculatively executed operations that >> have been abandoned for a branch mispredict will not be counted. So I think operation might >> be more accurate. > > Thanks, I see this note in the N2 PMU guide: > > """ > For PMU event definitions, some events specifically count > instructions, while other events count micro-operations (which are > referred to as operations). Please be aware of the use of the word > "operations" or "instructions" in the event description. > """ > > From your explanation I wasn't sure if operation was a superset of > instruction that included both retired and speculated ones, or whether > operation had another meaning. I don't see operation being used in the > micro-operation sense elsewhere in the ARM perf json, I think > micro-operation is more consistent and also clearer: > https://git.kernel.org/pub/scm/linux/kernel/git/acme/linux.git/tree/tools/perf/pmu-events/arch/arm64/arm/cortex-a75/pipeline.json?h=perf/core#n27 > > Perhaps the description can be something like: > Of all the micro-operations issued, what percentage were retired. A > lower number indicates bad speculation. > > An alternate way to add documentation is the perf wiki's glossary: > https://perf.wiki.kernel.org/index.php/Glossary > > I added the Neoverse N2 PMU Guide to: > https://perf.wiki.kernel.org/index.php/Useful_Links#Manuals >
Thanks.
The operation here is micro-operation, perhaps it is more accurate to change it to micro-operation.
Description of op_retired and op_spec: https://git.kernel.org/pub/scm/linux/kernel/git/acme/linux.git/tree/tools/perf/pmu-events/arch/arm64/common-and-microarch.json?h=perf/core#n315
The event of op_retired counts Micro-operation architecturally executed. The counter counts each operation counted by OP_SPEC that would be executed in a simple sequential execution of the program.
The event of op_spec counts Micro-operation speculatively executed. The counter counts the number of operations executed by the processing element, including those that are executed speculatively and would not be executed in a simple sequential execution of the program.
So "op_retired/op_spec" is indeed "of all the micro-operations issued, what percentage were retired". But not "a lower number indicates bad speculation". I think "retired" here means "committed".
In the N2 PMU guide: """ If the branch is mispredicted, and the instructions are speculatively executed, they will not be considered architecturally executed. The Arm® Architecture Reference Manual also refers to architecturally executed instructions as “retired” or “committed”. Speculatively executed instructions that are not architecturally executed will be abandoned; that is, their results will be discarded and not counted as part of the program flow. """
> >>>> + "MetricGroup": "PEutilization", >>>> + "MetricName": "retired_rate", >>>> + "ScaleUnit": "100%" >>>> + }, >>>> + { >>>> + "MetricExpr": "1 - OP_RETIRED / OP_SPEC", >>> >>> Should OP_RETIRED be greater than OP_SPEC? In which case won't this >>> metric be negative? >>> >> >> OP_RETIRED will not be greater than OP_SPEC. OP_SPEC counts any operation that has been >> speculatively executed. OP_SPEC is a superset of the OP_RETIRED event. There is a >> description about OP_SPEC and OP_RETIRED in this neoverse-n2 document. >> Link: https://documentation-service.arm.com/static/62cfe21e31ea212bb6627393?token= >> >>>> + "PublicDescription": "Fraction of operations wasted", >>>> + "BriefDescription": "Fraction of operations wasted", >>>> + "MetricGroup": "PEutilization", >>>> + "MetricName": "wasted_rate", >>>> + "ScaleUnit": "100%" >>>> + }, >>>> + { >>>> + "MetricExpr": "OP_RETIRED / OP_SPEC * (1 - (STALL_SLOT - CPU_CYCLES) / (CPU_CYCLES * 5))", >>>> + "PublicDescription": "Utilization of CPU", >>>> + "BriefDescription": "Utilization of CPU", >>> >>> Some more detail in the description would be useful. >>> >> >> Ok, I'll describe it in more detail. CPU_utilization reflects the truly effective ratio of operation >> executed by the CPU, which means that misprediction and stall are not included. Note that stall_slot >> minus cpu_cycles is a correction to the stall_slot error count. >> >>>> + "MetricGroup": "PEutilization", >>>> + "MetricName": "cpu_utilization", >>>> + "ScaleUnit": "100%" >>>> } >>>> ] >>>> -- >>>> 1.8.3.1 >>>>
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