linux-kernel - Re: perf can't keep up with mmap data

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Message-ID: <20100719150433.GB5222@ghostprotocols.net>
Date:	Mon, 19 Jul 2010 12:04:33 -0300
From:	Arnaldo Carvalho de Melo <acme@...hat.com>
To:	Christoph Hellwig <hch@....de>
Cc:	a.p.zijlstra@...llo.nl, paulus@...ba.org, mingo@...e.hu,
	linux-kernel@...r.kernel.org
Subject: Re: perf can't keep up with mmap data

Em Mon, Jul 19, 2010 at 09:48:13AM +0200, Christoph Hellwig escreveu:
> When running current -tip perf in my 32-bit x86 kvm guest I get lots
> of messages like:
> 
> WARNING: failed to keep up with mmap data.
> 
> when starting perf top, and still quite a few everytime it refreshes the
> display.

Should be better reported, probably with a message suggesting to use:

perf top -r RTPRIO

or to reduce the sampling frequency:

perf top -F 500

to have:

   PerfTop: 287 irqs/sec  kernel:40.8%  exact:  0.0% [500Hz cycles], (all, 2 CPUs)

Instead of the default:

   PerfTop:  35 irqs/sec  kernel:25.7%  exact:  0.0% [1000Hz cycles], (all, 2 CPUs)

- Arnaldo
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