Messages in this thread | | | From | Ian Rogers <> | Date | Fri, 2 Dec 2022 12:05:04 -0800 | Subject | Re: [PATCH v3 5/6] perf vendor events arm64: Add PE utilization metrics for neoverse-n2 |
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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, Ian
> >> + "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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