On 22/11/2022 07:11, Jing Zhang wrote:

在 2022/11/21 下午7:51, James Clark 写道:

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On 16/11/2022 15:26, Jing Zhang wrote:

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在 2022/11/16 下午7:19, James Clark 写道:

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On 31/10/2022 11:11, Jing Zhang wrote:

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This series add six metricgroups for neoverse-n2, among which, the
formula of topdown L1 is from the document:
https://documentation-service.arm.com/static/60250c7395978b529036da86?token=

Since neoverse-n2 does not yet support topdown L2, metricgroups such
as Cache, TLB, Branch, InstructionsMix, and PEutilization are added to
help further analysis of performance bottlenecks.

Hi Jing,

Thanks for working on this, these metrics look ok to me in general,
although we're currently working on publishing standardised metrics
across all new cores as part of a new project in Arm. This will include
N2, and our ones are very similar (or almost identical) to yours,
barring slightly different group names, metric names, and differences in
things like outputting topdown metrics as percentages.

We plan to publish our standard metrics some time in the next 2 months.
Would you consider holding off on merging this change so that we have
consistant group names and units going forward? Otherwise N2 would be> the odd one out. I will send you the metrics when they are ready, and we
will have a script to generate perf jsons from them, so you can review.

Do you mean that after you release the new standard metrics, I remake my
patch referring to them, such as consistent group names and unit?

Hi Jing,

I was planning to submit the patch myself, but there will be a script to
generate perf json files, so no manual work would be needed. Although
this is complicated by the fact that we won't be publishing the fixed
TopdownL1 metrics that you have for the existing N2 silicon so there
would be a one time copy paste to fix that part.

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We also have a slightly different forumula for one of the top down
metrics which I think would be slightly more accurate. We don't have

The v2 version of the patchset updated the formula of topdown L1.
Link: https://lore.kernel.org/all/1668411720-3581-1-git-send-email-renyu.zj@linux.alibaba.com/ (local)

The formula of the v2 version is more accurate than v1, and it has been
verified in our test environment. Can you share your formula first and we
can discuss it together? :)

I was looking at v2 but replied to the root of the thread by mistake. I
also had it the wrong way round. So your version corrects for the errata
on the current version of N2 (as you mentioned in the commit message).
Our version would be if there is a future new silicon revision with that
fixed, but it does have an extra improvement by subtracting the branch
mispredicts.

Perf doesn't currently match the jsons based on silicon revision, so
we'd have to add something in for that if a fixed silicon version is
released. But this is another problem for another time.

Hi James,

Let's do what Ian said, and you can improve it later with the standard metrics,
after the fixed silicon version is released.

Ok that's fine by me. I do have one update about our publishing progress
to share. This is the (currently empty) repo that we will be holding our
metrics in: https://gitlab.arm.com/telemetry-solution/telemetry-solution

We'll also have the conversion script in there as well. So there has at
least been some progress and we're getting close. I will keep you
updated when it is populated.

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This is the frontend bound metric we have for future revisions:

	"100 * ( (STALL_SLOT_FRONTEND/(CPU_CYCLES * 5)) - ((BR_MIS_PRED *
4)/CPU_CYCLES) )"

Other changes are, for example, your 'wasted' metric, we have
'bad_speculation', and without the
cycles subtraction:

	100 * ( ((1 - (OP_RETIRED/OP_SPEC)) * (1 - (STALL_SLOT/(CPU_CYCLES *
5)))) + ((BR_MIS_PRED * 4)/CPU_CYCLES) )

Thanks for sharing your metric version, But I still wonder, is BR_MIS_PRED not classified
as frontend bound? 

We're counting branch mispredicts as an extra cost so we subtract it
from frontend_bound because branch related stalls are covered by
bad_speculation where we have added BR_MIS_PRED instead of subtracting.

Unfortunately I'm just the middle man here, I didn't actually work
directly on producing these metrics so I hope nothing gets lost in my
explanation.

How do you judge the extra improvement by subtracting branch mispredicts?

As far as I know the repo that I mentioned above will have some
benchmarks and tooling that were used to validate our version. So it
should be apparent by running those.

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And some more details filled in around the units, for example:

    {
        "MetricName": "bad_speculation",
        "MetricExpr": "100 * ( ((1 - (OP_RETIRED/OP_SPEC)) * (1 -
(STALL_SLOT/(CPU_CYCLES * 5)))) + ((BR_MIS_PRED * 4)/CPU_CYCLES) )",
        "BriefDescription": "Bad Speculation",
        "PublicDescription": "This metric is the percentage of total
slots that executed operations and didn't retire due to a pipeline
flush.\nThis indicates cycles that were utilized but inefficiently.",
        "MetricGroup": "TopdownL1",
        "ScaleUnit": "1percent of slots"
    },

My "wasted" metric was changed according to the arm documentation description, it was originally
"bad_speculation".  I will change "wasted" back to "bad_speculation", if you wish.

Yeah that would be good. I think since that document we've tried to
align names more to what was already out there and bad_speculation was
probably judged to be a better description. For example it's already
used in tools/perf/pmu-events/arch/arm64/hisilicon/hip08/metrics.json

Thanks,
Jing

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So ignoring the errata issue, the main reason to hold off is for
consistency and churn because these metrics in this format will be
released for all cores going forwards.

Thanks
James

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