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

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Message-ID: <2d52edc4-c6e6-b641-b291-d1726cc20b30@arm.com>
Date:   Tue, 8 Feb 2022 15:58:55 +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 27/01/2022 11:42, Andrew Kilroy wrote:
> 
> 
> 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.
> 

Thanks for the feedback on this RFC, I think we'll resubmit these 
patches at a later time, when we've got a json metrics file or two.

Thanks,
Andrew