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From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: Grant Grundler <grundler@parisc-linux.org>
Cc: Andi Kleen <ak@suse.de>,
	James Bottomley <James.Bottomley@SteelEye.com>,
	axboe@suse.de, davem@redhat.com, suparna@in.ibm.com,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	alex_williamson@hp.com, bjorn_helgaas@hp.com
Subject: Re: [RFC] block layer support for DMA IOMMU bypass mode II
Date: 02 Jul 2003 22:16:39 +0100	[thread overview]
Message-ID: <1057180598.20318.32.camel@dhcp22.swansea.linux.org.uk> (raw)
In-Reply-To: <20030702165510.GC11739@dsl2.external.hp.com>

On Mer, 2003-07-02 at 17:55, Grant Grundler wrote:
> On Wed, Jul 02, 2003 at 01:57:01AM +0200, Andi Kleen wrote:
> > The K8 IOMMU cannot support this virtually contiguous thing. The reason
> > is that there is no guarantee that an entry in a sglist is a multiple
> > of page size.  And the aperture can only map 4K sized chunks, like 
> > a CPU MMU. So e.g. when you have an sglist with multiple 1K entries there is 
> > no way to get them continuous in IOMMU space (short of copying)
> 
> Can two adjacent IOMMU entries be used to map two 1K buffers?
> Assume the 1st buffer ends on a 4k alignment and the next one
> starts on a 4k alignment.

When I played with optimising merging on some 2.4 I2O and aacraid
controller stuff I found two things

1.	We allocate pages in reverse order so most merges cant occur
2.	If you use a 4K fs as most people do now the issue is irrelevant
3.	Almost every 1K mergable was part of the same 4K page anyway


  parent reply	other threads:[~2003-07-02 21:05 UTC|newest]

Thread overview: 52+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2003-07-01 16:46 [RFC] block layer support for DMA IOMMU bypass mode James Bottomley
2003-07-01 17:09 ` Andi Kleen
2003-07-01 17:28   ` James Bottomley
2003-07-01 17:42     ` Andi Kleen
2003-07-01 19:22       ` Grant Grundler
2003-07-01 19:56       ` James Bottomley
2003-07-01 17:54     ` H. Peter Anvin
2003-07-01 19:19 ` Grant Grundler
2003-07-01 19:59   ` Alex Williamson
2003-07-01 20:11     ` James Bottomley
2003-07-01 20:03   ` James Bottomley
2003-07-01 23:01     ` Grant Grundler
2003-07-02 15:52       ` James Bottomley
2003-07-01 22:51 ` David S. Miller
2003-07-01 23:57 ` [RFC] block layer support for DMA IOMMU bypass mode II Andi Kleen
2003-07-02  0:03   ` David S. Miller
2003-07-02  0:22     ` Andi Kleen
2003-07-02  0:21       ` David S. Miller
2003-07-02 16:53       ` Grant Grundler
2003-07-02 17:19         ` Andi Kleen
2003-07-02 16:55   ` Grant Grundler
2003-07-02 17:20     ` Andi Kleen
2003-07-02 17:37       ` Grant Grundler
2003-07-02 21:16     ` Alan Cox [this message]
2003-07-02 23:56       ` Andi Kleen
2003-07-03 20:26         ` Alan Cox
2003-07-03 21:24           ` Andi Kleen
2003-07-03 22:19             ` Grant Grundler
2003-07-08  2:14             ` David S. Miller
2003-07-08 19:34               ` Andi Kleen
2003-07-08 19:47                 ` Jeff Garzik
2003-07-08 20:10                   ` Andi Kleen
2003-07-08 20:11                   ` Grant Grundler
2003-07-08 22:04                 ` David S. Miller
2003-07-08 22:25                   ` Grant Grundler
2003-07-08 22:23                     ` David S. Miller
2003-07-09 18:55                       ` Andi Kleen
2003-07-23 11:40                       ` Grant Grundler
2003-07-28 11:15                         ` Andi Kleen
2003-07-28 14:59                           ` Grant Grundler
2003-07-30  2:31                           ` Grant Grundler
2003-08-01 21:51                             ` Cliff White
2003-08-01 23:18                               ` reaim now available as osdl-aim-7 - " Cliff White
2003-07-30  4:42                           ` Grant Grundler
2003-07-30  4:51                             ` David S. Miller
2003-07-30 13:06                               ` Grant Grundler
2003-07-30 16:02                               ` Grant Grundler
2003-07-30 16:36                                 ` Andi Kleen
2003-07-30 17:18                                   ` James Bottomley
2003-07-30 14:20                             ` James Bottomley
2003-07-23 13:20                       ` Grant Grundler
2003-07-23 15:30                         ` Jens Axboe

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