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Date: Tue, 30 Sep 2008 13:22:41 +0200
From: Ingo Molnar <mingo@elte.hu>
To: Sitsofe Wheeler <sitsofe@yahoo.com>
Cc: linux-kernel@vger.kernel.org, Peter Zijlstra <a.p.zijlstra@chello.nl>,
       Arjan van de Ven <arjan@infradead.org>,
       Steven Rostedt <rostedt@goodmis.org>
Subject: Re: How how latent should non-preemptive scheduling be?
Message-ID: <20080930112241.GC21367@elte.hu>
References: <20080922115749.GE14301@elte.hu> <48D88DB4.9020003@yahoo.com> <20080923115323.GA27240@elte.hu> <48D919A9.5000708@yahoo.com> <48D9460C.5040504@yahoo.com> <48D96725.1080909@yahoo.com> <20080927204834.GA31650@elte.hu> <48DFEF8A.3000502@yahoo.com> <20080929083709.GD18663@elte.hu> <48E16097.8060905@yahoo.com>
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* Sitsofe Wheeler <sitsofe@yahoo.com> wrote:

>              cat-7717  [000]  1392.941867: __tasklet_schedule <-ath5k_intr
>              cat-7717  [000]  1393.005963: __tasklet_schedule <-ath5k_intr
>              cat-7717  [000]  1393.033222: __switch_to <-schedule
>
> Here a schedule seemingly doesn't happen for a few hundredths of a second...

that's about 60 msecs. ath5k_intr IRQ handling overhead? IRQ handlers 
are non-preemptible. (even under CONFIG_PREEMPT=y)

	Ingo