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From: FUJITA Tomonori <>
Subject: Re: more iommu sg merging fallout
Date: Thu, 07 Feb 2008 08:53:33 +0900	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Wed, 06 Feb 2008 15:18:55 -0800 (PST)
David Miller <> wrote:

> From: FUJITA Tomonori <>
> Date: Thu, 07 Feb 2008 08:12:36 +0900
> > Really sorry about it.
> I am happy to test patches you send to me in the future :-)

Thanks a lot.

> > PARISC, Alpha, and IA64 IOMMUs use the two-pass algorithm like SPARC
> > but their first pass decides how to merge sg entires (and stores that
> > information in the sg entries), then the second pass simpliy follows
> > it (Hopefully I understand these IOMMUs correctly, or else I break
> > them too).
> For now I've removed all of the merging code from the sparc64 IOMMU
> support so that other users do not get corrupt filesystems.  It
> basically mimicks how the intel-iommu code works, ie. no attempts to
> merge anything.

I've just saw it.

> I intend to put merging back in, perhaps something similar to
> powerpc's merging logic but without the expensive (in my opinion)
> IOMMU allocation every loop.  I think it is better to determine the
> segment breaks in one pass, allocate that many IOMMU entries in one
> allocation, then fill them all in.

I thought about asking you if I can modify the SPARC IOMMUs to do
allocation in every loop.

The reason why I need the allocation in every loop is that I also need
to fix the problem that IOMMUs allocate memory areas without
considering a low level driver's segment boundary limits.

As far as I know, all the IOMMUs except for SPARC allocate a free area
in every loop but if it's too expensive for SPARC, then we need to
find a different way to handle segment boundary limits.

> Ideally, we should have some generic code that does all of this.
> Then you would only need to test one implementation.
> It is definitely doable and increasingly necessary as we have so
> many reimplementations of what is essentially identical core code.

Agreed though it's a very hard task.

  reply	other threads:[~2008-02-06 23:54 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-02-06  4:41 David Miller
2008-02-06 23:12 ` FUJITA Tomonori
2008-02-06 23:18   ` David Miller
2008-02-06 23:53     ` FUJITA Tomonori [this message]
2008-02-07  0:01       ` David Miller
2008-02-07  1:38         ` FUJITA Tomonori
2008-02-12  5:40           ` David Miller
2008-02-16  6:03             ` FUJITA Tomonori
2008-02-18  7:41               ` David Miller
2008-02-19 10:57                 ` FUJITA Tomonori
2008-02-21  6:56                   ` David Miller

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