[Xen-devel] Re: [ofa-general] Re: mthca use of dma_sync_single i

To:	"Michael S. Tsirkin" <mst@xxxxxxxxxxxxxxxxxx>
Subject:	[Xen-devel] Re: [ofa-general] Re: mthca use of dma_sync_single is bogus
From:	Roland Dreier <rdreier@xxxxxxxxx>
Date:	Tue, 10 Jul 2007 12:25:59 -0700
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Cc:	Lukas Hejtmanek <xhejtman@xxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, Keir Fraser <keir@xxxxxxxxxxxxx>, general@xxxxxxxxxxxxxxxxxxxxx
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In-reply-to:	<20070710183006.GE11320@xxxxxxxxxxxxxx> (Michael S. Tsirkin's message of "Tue, 10 Jul 2007 21:30:06 +0300")
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 > Hmm. This means there's no way to sync a range within
 > mapping created with map_sg?

It doesn't seem that there is one right now at least.

 > > It actually doesn't look too bad to replace our use of pci_map_sg()
 > > with dma_map_single(), at least at first glance.  I'll try to write a
 > > patch later.
 > 
 > Well, the reason map_sg is there is presumably because on some
 > architectures it's worth it to try and make the region contigious in DMA 
 > space.
 > But I agree this seems the lesser evil at this point ...

Given that we're already trying to allocate big chunks of physically
contiguous memory, I think that any virtual merging we get is likely
to be of very small benefit.

It is kind of a shame to give this up though.

 - R.

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[Xen-devel] Re: [ofa-general] Re: mthca use of dma_sync_single is bogus