Date: Thu, 18 Sep 2003 18:45:38 +1000 From: Peter Jeremy <PeterJeremy@optushome.com.au> To: Andrew Gallatin <gallatin@cs.duke.edu> Cc: freebsd-hackers@freebsd.org Subject: Re: PCI interrupts passing DMA Message-ID: <20030918084538.GB19197@cirb503493.alcatel.com.au> In-Reply-To: <16232.56412.745069.248974@grasshopper.cs.duke.edu> References: <16232.56412.745069.248974@grasshopper.cs.duke.edu>
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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
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