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Subject: Re: [patch] Real-Time Preemption, -RT-2.6.10-rc2-mm3-V0.7.32-6
From: Lee Revell <rlrevell@joe-job.com>
To: Esben Nielsen <simlo@phys.au.dk>
Cc: Mark_H_Johnson@raytheon.com, Florian Schmidt <mista.tapas@gmx.net>,
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Date: Thu, 09 Dec 2004 15:16:13 -0500
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On Thu, 2004-12-09 at 20:04 +0100, Esben Nielsen wrote:
> IRQ threading makes the system more predictable but for many, many
> devices it is very expensive. I am predicting that many interrupt routines 
> have to be turned back to running in interrupt context.

It's important to keep in mind that for the type of applications that
would want PREEMPT_DESKTOP, the IRQ threading is only necessary because
of the amount of work the IDE subsystem does in hardirq context.  There
was some discussion a while back and Jens posted a patch to move the IDE
IO completion to a softirq.  IIRC there was not a lot of comment on it.
But, it seems to me that this approach would give the most favorable
balance of performance and low latency for many uses.  My tests show
that with softirq preemption this should allow jackd to run at 64 frames
or so without IRQ threading.

Lee