Subject: Re: [RFC][PATCH 0/9] perf trace: support for general-purpose
 scripting
From: Peter Zijlstra <peterz@infradead.org>
To: Ingo Molnar <mingo@elte.hu>
Cc: Tom Zanussi <tzanussi@gmail.com>, linux-kernel@vger.kernel.org,
       fweisbec@gmail.com, rostedt@goodmis.org, lizf@cn.fujitsu.com,
       hch@infradead.org
In-Reply-To: <20091006090954.GA19325@elte.hu>
References: <1254809398-8078-1-git-send-email-tzanussi@gmail.com>
	 <20091006090954.GA19325@elte.hu>
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Date: Tue, 06 Oct 2009 15:25:54 +0200
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On Tue, 2009-10-06 at 11:09 +0200, Ingo Molnar wrote:
> * Tom Zanussi <tzanussi@gmail.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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