linux-kernel - Re: [PATCH] quiet down swiotlb warnings

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Message-ID: <20070602164704.GQ7217@one.firstfloor.org>
Date:	Sat, 2 Jun 2007 18:47:04 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Muli Ben-Yehuda <muli@...ibm.com>
Cc:	Andi Kleen <andi@...stfloor.org>, Rik van Riel <riel@...hat.com>,
	Andrew Vasquez <andrew.vasquez@...gic.com>,
	Christoph Hellwig <hch@...radead.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] quiet down swiotlb warnings

On Sat, Jun 02, 2007 at 06:21:46PM +0300, Muli Ben-Yehuda wrote:
> On Fri, Jun 01, 2007 at 10:26:01PM +0200, Andi Kleen wrote:
> 
> > Normally swiotlb doesn't even try to bounce when dma mask is <=
> > end_pfn so something must be very wrong in your kernel. It
> > definitely isn't a mainline kernel. If this happens in Xen then Xen
> > just needs fixing -- it should not try to bounce when the normal
> > kernel wouldn't.
> 
> Xen needs to bounce when the requested buffer is not contiguous in
> machine memory (and indeed uses swiotlb for that).

Then it should just restrict the sg list merging at the block layer
to never merge into anything larger than a page. Then this cannot
happen or only very rarely.

-Andi
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