linux-kernel - Re: [PATCH] perf data: export to JSON

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Message-ID: <2d78b018-df5a-36cb-2f78-d3ca11bf9513@codeweavers.com>
Date:   Wed, 31 Mar 2021 06:38:16 -0400
From:   Nicholas Fraser <nfraser@...eweavers.com>
To:     Jiri Olsa <jolsa@...hat.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>,
        Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>,
        Stephane Eranian <eranian@...gle.com>,
        Tan Xiaojun <tanxiaojun@...wei.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf data: export to JSON

Hi Jiri,

Thanks for the review. I've addressed your suggestions; some notes are
below. I'll send a new patch.

On 2021-03-24 2:20 p.m., Jiri Olsa wrote:
> On Wed, Mar 24, 2021 at 09:06:50AM -0400, Nicholas Fraser wrote:
>> [...] We use this to import the data into a tool on Windows
>> where integrating perf or libbabeltrace is impractical.
> 
> hi,
> exciting ;-) and curious, which tool is that?
> 

The tool is called gpuvis. The perf JSON parsing support is here:

https://github.com/ludocode/gpuvis

The idea is to be able to line up samples from perf with GPU trace events, so
you can do things like timebox all perf samples in a particular frame of
rendering.

> we already have zstd support compiled in for compressing samples,
> should be easy to use it for compressing the output of this right
> away

This would require that apps that consume this integrate zstd as well. It's
simpler (both conceptually and from an integration standpoint) to just compress
on command-line if you need with whatever compressor you want. You can even do
this inline by writing to /dev/stdout, e.g.:

    perf data convert --to-json /dev/stdout --force | zstd > out.json.zstd

Since we're transferring to Windows, more likely we'd output the JSON and then
put it in a .zip container.

> I understand not supporting opts.all or opts.tod, but 'force'
> support means just assigning 'force' to struct perf_data

It's not clear to me what 'force' does on 'struct perf_data' since we're only
reading it. I assumed for data export it meant the output file should be
overwritten. I've made it do both in the replacement patch.

Nick