linux-kernel - Re: [Intel IOMMU 00/10] Intel IOMMU support, take #2

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Date:	Tue, 26 Jun 2007 17:36:58 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Muli Ben-Yehuda <muli@...ibm.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Keshavamurthy, Anil S" <anil.s.keshavamurthy@...el.com>,
	linux-kernel@...r.kernel.org, gregkh@...e.de,
	suresh.b.siddha@...el.com, arjan@...ux.intel.com,
	ashok.raj@...el.com, davem@...emloft.net, clameter@....com
Subject: Re: [Intel IOMMU 00/10] Intel IOMMU support, take #2

On Tue, Jun 26, 2007 at 11:09:40AM -0400, Muli Ben-Yehuda wrote:
> On Tue, Jun 26, 2007 at 05:56:49PM +0200, Andi Kleen wrote:
> 
> > > > - The IOMMU can merge sg lists into a single virtual block. This could
> > > > potentially speed up SG IO when the device is slow walking SG
> > > > lists.  [I long ago benchmarked 5% on some block benchmark with
> > > > an old MPT Fusion; but it probably depends a lot on the HBA]
> > > 
> > > But most devices are SG-capable.
> > 
> > Your point being?
> 
> That the fact that an IOMMU can do SG for non-SG-capble cards is not
> interesting from a "reason for inclusion" POV.

You misunderstood me; my point was that some SG capable devices
can go faster if they get shorter SG lists.

But yes for non SG capable devices it is also interesting. I expect
it will obsolete most users of that ugly external patch to allocate large
memory areas for IOs. That's a point I didn't mention earlier.

> > Also the user interface for X server case needs more work.
> 
> Is anyone working on it?

It's somewhere on the todo list.


-Andi
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