linux-kernel - Re: [PATCH 5/6] perf_counter: kerneltop: mmap

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Date:	Wed, 25 Mar 2009 13:57:12 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	linux-kernel@...r.kernel.org, Paul Mackerras <paulus@...ba.org>,
	Mike Galbraith <efault@....de>,
	Arjan van de Ven <arjan@...radead.org>,
	Wu Fengguang <fengguang.wu@...el.com>
Subject: Re: [PATCH 5/6] perf_counter: kerneltop: mmap_pages argument

On Wed, 2009-03-25 at 13:54 +0100, Ingo Molnar wrote:
> * Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> 
> > On Wed, 2009-03-25 at 13:35 +0100, Ingo Molnar wrote:
> > 
> > > > Also, when mixing streams (events,mmap) is a single: you missed 
> > > > 'n' events still good?
> > > 
> > > How would such mixing work? Multiple counters streaming into the 
> > > same mmap area?
> > 
> > No basically having overflow events and mmap-vma changed events in 
> > a single output stream.
> 
> ah, and i missed the impact of variable size records - that too 
> makes it somewhat impractical to emit overflow records in situ. (the 
> kernel does not really know the precise start of the previous 
> record, typically.)

Alternatively, we could simply not emit new events until the read
position increases,. that's much simpler.

Still don't like mapping the stuff writable though..

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