linux-kernel - Re: [RFC PATCH 00/12] Topdown parser

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Date:   Wed, 11 Nov 2020 13:46:46 -0800
From:   Andi Kleen <ak@...ux.intel.com>
To:     Ian Rogers <irogers@...gle.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-kernel@...r.kernel.org, Jin Yao <yao.jin@...ux.intel.com>,
        John Garry <john.garry@...wei.com>,
        Paul Clarke <pc@...ibm.com>, kajoljain <kjain@...ux.ibm.com>,
        Stephane Eranian <eranian@...gle.com>,
        Sandeep Dasgupta <sdasgup@...gle.com>,
        linux-perf-users@...r.kernel.org
Subject: Re: [RFC PATCH 00/12] Topdown parser

On Tue, Nov 10, 2020 at 02:03:34AM -0800, Ian Rogers wrote:
> This RFC is for a new tool that reads TMA_Metrics.csv as found on
> download.01.org/perfmon and generates metrics and metric groups from
> it. To show the functionality the TMA_Metrics.csv is downloaded, but
> an accepted change would most likely include a copy of this file from
> Intel. With this tool rather than just level 1 topdown metrics, a full
> set of topdown metrics to level 4 are generated.

I'm not sure I understand the motivation for making the spreadsheet parsing
part of the perf tool? It only needs to run once when the metrics are generated
to build perf.

FWIW I did something similar in python (that's how the current metrics
json files were generated from the spreadsheet) and it was a lot
simpler and shorter in a higher level language.

One problem I see with putting the full TopDown model into perf is 
that to do a full job it requires a lot more infrastructure that is
currently not implemented in metrics: like an event scheduler,
hierarchical thresholding over different nodes, SMT mode support etc.

I implemented it all in toplev, but it was a lot of work to get it all right.
I'm not saying it's not doable, but it will be a lot of additional work
to work out all the quirks using the metrics infrastructure.

I think adding one or two more levels is probably ok, but doing all levels
without these mechanisms might be difficult to use in the end.

-Andi