linux-kernel - Re: [00/15] swiotlb cleanup

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Message-Id: <20090713181558B.fujita.tomonori@lab.ntt.co.jp>
Date:	Mon, 13 Jul 2009 18:16:30 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	mingo@...e.hu
Cc:	Ian.Campbell@...citrix.com, jeremy@...p.org,
	linux-kernel@...r.kernel.org, linux-ia64@...r.kernel.org,
	linuxppc-dev@...abs.org, benh@...nel.crashing.org,
	tony.luck@...el.com, x86@...nel.org, beckyb@...nel.crashing.org,
	joerg.roedel@....com
Subject: Re: [00/15] swiotlb cleanup

On Mon, 13 Jul 2009 13:20:22 +0900
FUJITA Tomonori <fujita.tomonori@....ntt.co.jp> wrote:

> On Fri, 10 Jul 2009 16:12:48 +0200
> Ingo Molnar <mingo@...e.hu> wrote:
> 
> > > functionality and reimplemented the surrounding infrastructure in 
> > > terms of that (and incorporating our additional requirements). I 
> > > prototyped this (it is currently unworking, in fact it seems to 
> > > have developed rather a taste for filesystems :-() but the 
> > > diffstat of my WIP patch is:
> > >
> > >          arch/x86/kernel/pci-swiotlb.c |    6 
> > >          arch/x86/xen/pci-swiotlb.c    |    2 
> > >          drivers/pci/xen-iommu.c       |  385 ++++++++++++++++++++++++++++++++++++++++--
> > >          include/linux/swiotlb.h       |   12 +
> > >          lib/swiotlb.c                 |   10 -
> > >          5 files changed, 385 insertions(+), 30 deletions(-)
> > >
> > > where a fair number of the lines in xen-iommu.c are copies of 
> > > functions from swiotlb.c with minor modifications. As I say it 
> > > doesn't work yet but I think it's roughly indicative of what such 
> > > an approach would look like. I don't like it much but am happy to 
> > > run with it if it looks to be the most acceptable approach. [...]
> > 
> > +400 lines of code to avoid much fewer lines of generic code impact 
> > on the lib/swiotlb.c side sounds like a bad technical choice to me. 
> 
> The amount of code is not the point. The way to impact on the
> lib/swiotlb.c is totally wrong from the perspective of the kernel
> design; it uses architecture code in the very original (xen) way.

btw, '+400 lines of code to avoid much fewer lines of generic code
impact on the lib/swiotlb.c' doesn't sound true to me.

Here is a patch in the way that Xen people want to do:

http://patchwork.kernel.org/patch/26343/

---
 arch/x86/Kconfig                 |    4 +
 arch/x86/include/asm/io.h        |    2 +
 arch/x86/include/asm/pci_x86.h   |    1 +
 arch/x86/include/asm/xen/iommu.h |   12 ++
 arch/x86/kernel/pci-dma.c        |    3 +
 arch/x86/pci/Makefile            |    1 +
 arch/x86/pci/init.c              |    6 +
 arch/x86/pci/xen.c               |   51 +++++++
 drivers/pci/Makefile             |    2 +
 drivers/pci/xen-iommu.c          |  271 ++++++++++++++++++++++++++++++++++++++


Even with the way that Xen people want to do, drivers/pci/xen-iommu.c
is about 300 lines. And my patchset removes the nice amount of lines
for dom0 support. I don't see much difference wrt lines.
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