linux-kernel - Re: [PATCH RFC 4/9] perf jevents: Add sys_events_find_events

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Date:   Fri, 14 Jul 2023 12:58:36 +0100
From:   John Garry <john.g.garry@...cle.com>
To:     Ian Rogers <irogers@...gle.com>
Cc:     acme@...nel.org, namhyung@...nel.org, jolsa@...nel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        renyu.zj@...ux.alibaba.com, shangxiaojing@...wei.com,
        kjain@...ux.ibm.com, kan.liang@...ux.intel.com
Subject: Re: [PATCH RFC 4/9] perf jevents: Add sys_events_find_events_table()

On 13/07/2023 22:35, Ian Rogers wrote:
>>
>> {
>>                  "MetricExpr": "pmu_unit@...nt_foo@ * pmu_unit@...nt_bar@ * 2",
>>                  "MetricName": "metric_baz",
>> },
>> {
>>                  "EventCode": "0x84",
>>                  "EventName": "event_foo ",
>>                  "Compat": "0x00000040",
>>                  "Unit": "pmu_unit"
>> },
>> {
>>                  "EventCode": "0x85",
>>                  "EventName": "event_bar ",
>>                  "Compat": "0x00000040",
>>                  "Unit": "pmu_unit"
>> },
>>
>> And we have a pmu with name and hw id matching "pmu_unit" and
>> "0x00000040" present, that we select metric metric_baz for soc_b
> Not sure I'm fully understanding.With the sysfs layout we'd have to
> have a way of supporting CPUIDs, we could have a mapfile.csv style
> approach or perhaps encode the CPUID into the path. It is complex as
> CPUIDs are wildcards in the tool.

I am not sure why you mention CPUIDs. sys events and their metrics are 
matched only on Unit and Compat.

Furthermore, my solution here is based what we have today, and would not 
be based on this sysfs solution which you mention.

> 
>>> I think Unit may be useful, say on Intel
>>> hybrid I want the tma_fround_bound metric on just cpu_atom. Currently
>>> the use of Unit is messy for metrics, ie uncore metrics are associated
>>> with core PMUs, and what to do with a MetricExpr with >1 PMU. I think
>>> we're learning from trying. I'm just hoping the migration to a sysfs
>>> style layout will still be possible, as I can see lots of upside in
>>> terms of testing, 1 approach, etc.
>> Do you have an RFC or something for this "sysfs style layout"? I think
>> that it would be easier for me to understand your idea by seeing the SW.
> When I get a chance 😄 My thought is to first extend jevents.py to
> have a second output format, so sysfs style rather than pmu-events.c.
> This way we can merge the changes as a jevents.py feature even if we
> don't change the perf tool to support it.

ok, fine, but I would still like this progress this work now. It has 
been sitting around for some time and was really difficult to rebase 
(since I was not tumbling my baseline).

Thanks,
John