linux-kernel - Re: [PATCH 4/5] perf record: mmap output file

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Message-ID: <20131113121617.GL21461@twins.programming.kicks-ass.net>
Date:	Wed, 13 Nov 2013 13:16:17 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	David Ahern <dsahern@...il.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	linux-kernel@...r.kernel.org, jolsa@...hat.com,
	Frederic Weisbecker <fweisbec@...il.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Mike Galbraith <efault@....de>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 4/5] perf record: mmap output file - v5

On Wed, Nov 13, 2013 at 12:50:21PM +0100, Ingo Molnar wrote:
> 
> * Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > On Tue, Nov 12, 2013 at 10:11:21PM +0100, Ingo Molnar wrote:
> > > 
> > > * David Ahern <dsahern@...il.com> wrote:
> > > 
> > > > > Dunno.. it _should_ all work. Try it and see what it does.. Once the 
> > > > > events are bigger than a page things might get 'interesting' though.
> > > 
> > > Which could be the case with call-graph recording, right?
> > 
> > Not typically, I think we're limiting call graphs to 127 u64, which is 
> > ~1k. Maybe you can blow the single page if you also do a large 
> > top-of-stack copy for dwarf/unwind nonsense.
> 
> What I meant was dwarf style call graph recording:

Ah, one of those things I've never yet used ;-)

>  tools/perf/builtin-record.c:                    const unsigned long default_stack_dump_size = 8192;
> 
> Doesn't that mean 8K+ events?

Oh yes.. that's ideal to trigger this.
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