linux-kernel - Re: [PATCH 1/2] perf tools: Add reference timestamp to perf header

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Date:	Mon, 13 Dec 2010 15:43:30 -0200
From:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	"David S. Ahern" <daahern@...co.com>,
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] perf tools: Add reference timestamp to perf header

Em Mon, Dec 13, 2010 at 06:35:16PM +0100, Peter Zijlstra escreveu:
> On Mon, 2010-12-13 at 15:22 -0200, Arnaldo Carvalho de Melo wrote:
> > > No, the last one already happened, you cannot postpone the last one,
> > > there will always be another excuse.
> > 
> > Did you understand the use case? How to have multiple reference times
> > when appending?
> 
> Yes, I understood it perfectly, I just detest the existence of these
> pure user records, they need to die ASAP.

Heck, that was be the first I suggested to introduce ;-)
 
> > "last one" means adding a multiplexor, PERF_RECORD_LAST_ONE if you will,
> > and inside it we add new events if the need arises. Then never again we
> > add a PERF_RECORD_ event in userspace. 
> 
> Nah, that sucks too, the whole concept of pure user-space events in that
> stream sucks.
> 
> There's multiple things you can do, you could:
> 
>  - create a kernel event PERF_RECORD_NEW_BUFFER and stuff that into each
> fresh buffer when its created, it could contain all kinds of 1-time
> information, like:
> 	* this CLOCK_MONOTONIC offset (for what little good that does, since
> our clock isn't strictly sync'ed to CLOCK_MONOTONIC so we can incur
> arbitrary drift).
>  	* architecture details, like 64/32 host info needed for the
> PERF_SAMPLE_REGS stuff.
> 
>  - extend the existing header infrastructure to write a new header in
> front of the new stream. The main header already has a data section that

Ok, so for this specific case its just a matter of s/event/header/g ?
:-)

I.e. just add a new header when appending and have the size of the
"sessions" in each header? Fine with me as well, the information will be
at the same place I intended, i.e. before each recording session.

> points to the end of the stream, add a continuation header section that
> points to a continuation-header used to appends and record the clock
> offset data in there.
> 
>  - something else entirely.
> 
> Just stop using these stupid fake events and be somewhat creative.

Whatever, never introduced one, they are inserted, IIRC, in the
beggining of the stream, so I guess we can just do that sed and call
them headers and be done with it.

Will verify if that is the case.

- Arnaldo
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