linux-kernel - Re: more iommu sg merging fallout

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Message-Id: <20080207103801T.fujita.tomonori@lab.ntt.co.jp>
Date:	Thu, 07 Feb 2008 10:38:01 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	davem@...emloft.net
Cc:	fujita.tomonori@....ntt.co.jp, tomof@....org,
	jens.axboe@...cle.com, linux-kernel@...r.kernel.org
Subject: Re: more iommu sg merging fallout

On Wed, 06 Feb 2008 16:01:47 -0800 (PST)
David Miller <davem@...emloft.net> wrote:

> From: FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
> Date: Thu, 07 Feb 2008 08:53:33 +0900
> 
> > On Wed, 06 Feb 2008 15:18:55 -0800 (PST)
> > David Miller <davem@...emloft.net> wrote:
> > 
> > > 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.
> > 
> > http://linux.derkeiler.com/Mailing-Lists/Kernel/2007-11/msg07616.html
> > http://linux.derkeiler.com/Mailing-Lists/Kernel/2007-12/msg02286.html
> > 
> > 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.
> 
> Ok then what I'll do is adopt some version of powerpc's merging
> allocator into the sparc64 code.

Great, thanks! SPARC IOMMUs use bitmap for the free area management
like POWER IOMMUs so it could use lib/iommu-helper as POWER does.
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