linux-kernel - Re: [PATCHSET 00/16] perf top: Add multi-thread support (v1)

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Date:	Mon, 14 Dec 2015 07:55:32 -0700
From:	David Ahern <dsahern@...il.com>
To:	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>
Cc:	Namhyung Kim <namhyung@...il.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Jiri Olsa <jolsa@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Andi Kleen <andi@...stfloor.org>,
	Stephane Eranian <eranian@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>
Subject: Re: [PATCHSET 00/16] perf top: Add multi-thread support (v1)

On 12/14/15 2:38 AM, Ingo Molnar wrote:
>
>> And in an unrelated note, I absolutely detest --buildid being the
>> default, it makes perf-record blow chunks.

Yes, a .debug directory that gets bloated fast and being a dot-directory 
is off the primary radar. I forget about it and too often forget to add 
the option to disable it.

>
> So I'd absolutely _love_ to split up the singular perf.data into a hierarchy of
> files in a .perf directory, with a structure like this (4-core system):
>
> 	.perf/cmdline
> 	.perf/features
> 	.perf/evlist
> 	.perf/ring_buffers/cpu0/raw.trace
> 	.perf/ring_buffers/cpu1/raw.trace
> 	.perf/ring_buffers/cpu2/raw.trace
> 	.perf/ring_buffers/cpu3/raw.trace
> 	...

On a related note why a .perf directory?

>
> I.e. the current single file format of perf.data would be split up into individual
> files. Each CPU would get its own trace file output - any sorting and ordering
> would be done afterwards. 'perf record' itself would never by default have to do
> any of that, it's a pure recording session.
>
> 'perf archive' would still create a single file to make transport between machines
> easy.
>
> perf.data.old would be replaced by a .perf.old directory or so.
>
> Debugging would be easier too I think, as there's no complex perf data format
> anymore, it's all in individual (typically text, or binary dump) files in the
> .perf directory.
>
> This would solve all the scalability problems - and would make the format more
> extensible and generally more accessible as well.
>
> What do you think?

Big change to user experience.

I realize perf-archive has been around since I started using perf in 
mid-2010, but I for one never use it. I suspect it is not widely used 
(definitely not in the circles I have been involved and helped with 
perf), so suddenly requiring it is a change in user experience.

The only 2 files on the system I pull off the box are kallsyms and 
perf.data. Most of the systems where I use perf have limited symbols and 
there is nothing in .debug I need to pull of the box.

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