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

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Message-Id: <FF72C10D-2755-4B85-8714-8C35F34FED69@kernel.crashing.org>
Date:	Wed, 15 Jul 2009 15:24:33 -0500
From:	Becky Bruce <beckyb@...nel.crashing.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	beckyb@...nel.crashing.org, Jeremy Fitzhardinge <jeremy@...p.org>,
	tony.luck@...el.com, linux-ia64@...r.kernel.org,
	Ian Campbell <Ian.Campbell@...rix.com>, x86@...nel.org,
	"linux-kernel@...r.kernel.org Mailing List" 
	<linux-kernel@...r.kernel.org>,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	"linuxppc-dev@...abs.org list" <linuxppc-dev@...abs.org>,
	Joerg Roedel <joerg.roedel@....com>
Subject: Re: [00/15] swiotlb cleanup


On Jul 13, 2009, at 10:13 PM, Becky Bruce wrote:

>
> On Jul 10, 2009, at 12:12 AM, Ingo Molnar wrote:
>
>>
>> * FUJITA Tomonori <fujita.tomonori@....ntt.co.jp> wrote:
>>
>>> - removes unused (and unnecessary) hooks in swiotlb.
>>>
>>> - adds dma_capable() and converts swiotlb to use it. It can be  
>>> used to
>>> know if a memory area is dma capable or not. I added
>>> is_buffer_dma_capable() for the same purpose long ago but it turned
>>> out that the function doesn't work on POWERPC.
>>>
>>> This can be applied cleanly to linux-next, -mm, and mainline. This
>>> patchset touches multiple architectures (ia64, powerpc, x86) so I
>>> guess that -mm is appropriate for this patchset (I don't care much
>>> what tree would merge this though).
>>>
>>> This is tested on x86 but only compile tested on POWERPC and IA64.
>>>
>>> Thanks,
>>>
>>> =
>>> arch/ia64/include/asm/dma-mapping.h    |   18 ++++++
>>> arch/powerpc/include/asm/dma-mapping.h |   23 +++++++
>>> arch/powerpc/kernel/dma-swiotlb.c      |   48 +---------------
>>> arch/x86/include/asm/dma-mapping.h     |   18 ++++++
>>> arch/x86/kernel/pci-dma.c              |    2 +-
>>> arch/x86/kernel/pci-gart_64.c          |    5 +-
>>> arch/x86/kernel/pci-nommu.c            |    2 +-
>>> arch/x86/kernel/pci-swiotlb.c          |   25 --------
>>> include/linux/dma-mapping.h            |    5 --
>>> include/linux/swiotlb.h                |   11 ----
>>> lib/swiotlb.c                          |  102 ++++++++ 
>>> +-----------------------
>>> 11 files changed, 92 insertions(+), 167 deletions(-)
>>
>> Hm, the functions and facilities you remove here were added as part
>> of preparatory patches for Xen guest support. You were aware of
>> them, you were involved in discussions about those aspects with Ian
>> and Jeremy but still you chose not to Cc: either of them and you
>> failed to address that aspect in the changelogs.
>>
>> I'd like the Xen code to become cleaner more than anyone else here i
>> guess, but patch submission methods like this are not really
>> helpful. A far better method is to be open about such disagreements,
>> to declare them, to Cc: everyone who disagrees, and to line out the
>> arguments in the changelogs as well - instead of just curtly
>> declaring those APIs 'unused' and failing to Cc: involved parties.
>>
>> Alas, on the technical level the cleanups themselves look mostly
>> fine to me. Ian, Jeremy, the changes will alter Xen's use of
>> swiotlb, but can the Xen side still live with these new methods - in
>> particular is dma_capable() sufficient as a mechanism and can the
>> Xen side filter out DMA allocations to make them physically
>> continuous?
>>
>> Ben, Tony, Becky, any objections wrt. the PowerPC / IA64 impact? If
>> everyone agrees i can apply them to the IOMMU tree, test it and push
>> it out to -next, etc.
>>
>
> Ingo,
>
> With the exception of the patch I commented on, I think these look  
> OK from the powerpc point of view.  I've successfully booted one of  
> my test platforms with the entire series applied and will run some  
> more extensive (i.e. not "Whee!  A prompt!") tests tomorrow.

Well, I am still testing.  I've observed one unexpected LTP testcase  
failure with these patches applied, but so far have been unable to  
reproduce it.  So these patches are probably OK, but I will look into  
this some more next week.

-Becky

>
>
> -Becky
>
> _______________________________________________
> Linuxppc-dev mailing list
> Linuxppc-dev@...ts.ozlabs.org
> https://lists.ozlabs.org/listinfo/linuxppc-dev

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