linux-kernel - Re: [RFC PATCH v2 0/5] topdown with metrics

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Date:   Thu, 27 Jan 2022 11:42:27 +0000
From:   Andrew Kilroy <andrew.kilroy@....com>
To:     John Garry <john.garry@...wei.com>, linux-kernel@...r.kernel.org,
        linux-perf-users@...r.kernel.org, acme@...nel.org,
        irogers@...gle.com, ak@...ux.intel.com
Cc:     Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>
Subject: Re: [RFC PATCH v2 0/5] topdown with metrics



On 20/01/2022 09:26, John Garry wrote:
> On 11/01/2022 15:07, Andrew Kilroy wrote:
>> This patch series adds the ability for the --topdown option to use
>> metrics (defined in json files in the pmu-events directory) to describe
>> how to calculate and determine the output columns for topdown level 1.
>>
>> For this to work, a number of metrics have to be defined for the
>> relevant processor with the MetricGroup name "TopDownL1".  perf will
>> arrange for the events defined in each metric to be collected, and each
>> metric will be displayed in the output, as if
>>
>>    perf stat -M 'TopDownL1' --metric-only -- exampleapp
>>
>> had been used.
>>
>> Topdown was already implemented where certain kernel events are defined.
>> If these kernel events are defined, the new json metrics behaviour is
>> not used.  The json metrics approach is only used if the kernel events
>> are absent.
>>
>> The last patch in the series disables the json metrics behaviour on x86.
>> This is because of concerns that due to SMT it's not straightforward to
>> express the various formulas as json for certain x86 cpus.  See
> 
> I suppose this solution is ok.
> 

Thanks, would you mind giving it a Reviewed-By?

> A concern is that today we only have 1x arm64 platform which actually 
> supports this in mainline.
> 
> Do you have any more which you plan to support?
> 

The Neoverse cores, mainly.

> I think that it's the frontend bound and fetch_bubble event which 
> doesn't have a standard arm solution.
> 
> Note that I do have a series for perf tool which can read arm cpu pmu 
> sysfs events folder to find events which are implemented (I don't think 
> all required events are mandated) and match that against the common arch 
> events JSON, so that we don't need a JSON definition file for each core 
> implementation from all implementators - this would improve scalability. 
> However a concern is that some events - like inst_spec - have imp def 
> meaning, so may not be good to always use by default for all cores metrics.
> 
> Thanks,
> John

Thanks,
Andrew