linux-kernel - Re: Performance counter API review was [patch] Performance Counters for Linux, v3

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Date:	Wed, 04 Feb 2009 11:51:44 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Paul Mackerras <paulus@...ba.org>
Cc:	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	Andi Kleen <andi@...stfloor.org>, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Stephane Eranian <eranian@...glemail.com>,
	Eric Dumazet <dada1@...mosbay.com>,
	Robert Richter <robert.richter@....com>,
	Arjan van de Veen <arjan@...radead.org>,
	Peter Anvin <hpa@...or.com>,
	"David S. Miller" <davem@...emloft.net>,
	Maynard Johnson <mpjohn@...ibm.com>, carll@...ibm.com
Subject: Re: Performance counter API review was [patch] Performance
 Counters for Linux, v3

On Wed, 2009-02-04 at 21:47 +1100, Paul Mackerras wrote:
> Peter Zijlstra writes:
> 
> > How is smp_call_function() going to help here? You still need to pull
> > all that data through that one FD. That's a cacheline bounce fest.
> 
> Well, let's put this into perspective.  We would be collecting 8 bytes
> of data from each CPU.  Hardly a "cacheline bounce fest". :)

Ah, I was thinking more of the event triggered profiling, like NMI time,
cachemiss or pagefault profiling.

In those cases you'd get a continuous stream of data for each cpu, at
possibly quite high speeds.

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