Subject: Re: [PATCH 5/6] perf_counter: kerneltop: mmap_pages argument
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Ingo Molnar <mingo@elte.hu>
Cc: linux-kernel@vger.kernel.org, Paul Mackerras <paulus@samba.org>,
       Mike Galbraith <efault@gmx.de>, Arjan van de Ven <arjan@infradead.org>,
       Wu Fengguang <fengguang.wu@intel.com>
In-Reply-To: <20090325125407.GA32744@elte.hu>
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	 <1237984864.7972.896.camel@twins>  <20090325125407.GA32744@elte.hu>
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Date: Wed, 25 Mar 2009 13:57:12 +0100
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On Wed, 2009-03-25 at 13:54 +0100, Ingo Molnar wrote:
> * Peter Zijlstra <a.p.zijlstra@chello.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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