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Date: Thu, 18 Sep 2003 18:45:38 +1000
From: Peter Jeremy <PeterJeremy@optushome.com.au>
To: Andrew Gallatin <gallatin@cs.duke.edu>
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cc: freebsd-hackers@freebsd.org
Subject: Re: PCI interrupts passing DMA
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On Wed, Sep 17, 2003 at 06:12:44PM -0400, Andrew Gallatin wrote:
>My question is: What the heck could the SMP kernel be doing which
>causes the DMA to "complete" faster?   

My guess is that this is a coherency issue rather than a timing issue.
The SMP kernels are far more careful about ensuring consistency
between CPUs and this could be fixing/masking the problem

That said, any decent disk controller uses DMA and if the UP kernel
really did have PCI-bus coherency problems (or massive delays), a
significant part of the user-base would be screaming.

The other possibility: Is your PCI card doing something wierd?  Are
you bending one of the PCI specs a bit far?

Peter