linux-kernel - Re: [RFC][PATCH 0/9] perf trace: support for general-purpose scripting

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Message-Id: <1254835554.21044.278.camel@laptop>
Date:	Tue, 06 Oct 2009 15:25:54 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Tom Zanussi <tzanussi@...il.com>, linux-kernel@...r.kernel.org,
	fweisbec@...il.com, rostedt@...dmis.org, lizf@...fujitsu.com,
	hch@...radead.org
Subject: Re: [RFC][PATCH 0/9] perf trace: support for general-purpose
 scripting

On Tue, 2009-10-06 at 11:09 +0200, Ingo Molnar wrote:
> * Tom Zanussi <tzanussi@...il.com> wrote:
> 
> > Known problems/shortcomings:
> > 
> > Probably the biggest problem right now is the sorting hack I added as 
> > the last patch.  It's just meant as a temporary thing, but is there 
> > because tracing scripts in general want to see events in the order 
> > they happened i.e. timestamp order. [...]
> 
> Btw., have you seen the -M/--multiplex option to perf record? It 
> multiplexes all events into a single buffer - making them all ordered. 
> (The events are in causal ordering in this case even if there's some TSC 
> asynchronity)

It also wrecks large machines.. I've been thinking about limiting the
number of CPUs you can redirect into a single output stream using the
output_fd thing, but then the inherited stuff makes that very hard.

And we also need a solution for the inhertited counters, the best would
be the per-cpu inherited things, where we use both cpu and pid, instead
of either.

In short, -M is nice, but it also has significant down sides, esp. with
machines getting more and more cores.

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