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Date: Thu, 29 Jul 2004 23:07:01 +0200
From: Ingo Molnar <mingo@elte.hu>
To: Pavel Machek <pavel@ucw.cz>
Cc: Scott Wood <scott@timesys.com>, Nick Piggin <nickpiggin@yahoo.com.au>,
       Lee Revell <rlrevell@joe-job.com>, Andrew Morton <akpm@osdl.org>,
       linux-audio-dev@music.columbia.edu, arjanv@redhat.com,
       linux-kernel <linux-kernel@vger.kernel.org>,
       "La Monte H.P. Yarroll" <piggy@timesys.com>
Subject: Re: [linux-audio-dev] Re: [announce] [patch] Voluntary Kernel Preemption Patch
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* Pavel Machek <pavel@ucw.cz> wrote:

> ...
> > [the only remaining source of 'latency uncertainty' is the small
> > asynchronous hardirq stub that would still remain. This has an effect
> > that can be compared to e.g. cache effects and it cannot become unbound
> > unless the CPU is bombarded with a very high number of interrupts.]
> 
> Well, I do not follow you I guess.
> 
> With large-enough number of hardirqs you do no progress at all.
> 
> Even if only "sane" number of irqs, if they all decide to hit within
> one getpid(), this getpid is going to take quite long....

yes, all of this assumes some _minimal_ sanity of the hardware
environment. We do detect interrupt storms and turn those IRQ sources
off, but there's no (sane) way to avoid interrupt storms from
driver-handled IRQ sources.

	Ingo