linux-kernel - Re: perf: [patch] regression with PERF_EVENT_IOC

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Date:	Tue, 31 May 2011 09:23:13 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Vince Weaver <vince@...ter.net>
Cc:	Vince Weaver <vweaver1@...s.utk.edu>, linux-kernel@...r.kernel.org,
	mingo@...e.hu, paulus@...ba.org, acme@...hat.com
Subject: Re: perf: [patch] regression with PERF_EVENT_IOC_REFRESH

On Mon, 2011-05-30 at 21:33 -0400, Vince Weaver wrote:
> the problem was the mentioned commit tried to optimize the use of 
> watermark and wakeup_watermark without taking into account that 
> wakeup_watermark is a union with wakeup_events. 

Note that wake_events isn't related to IOC_REFRESH, wake_events is how
much events to buffer in the mmap-buffer before issuing a wakeup.

IOC_REFRESH increments event_limit, which is how many events to run
before disabling yourself.

What I gather is that due to that SIGIO bug (fixed by f506b3dc0e), you
had to have both an mmap and a wakeup in order for that signal to
arrive.

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