linux-kernel - Re: [PATCH v2] mm: dmapool: use provided gfp flags for all dma_alloc

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Date:	Wed, 16 Jan 2013 23:36:35 +0100
From:	Soeren Moch <smoch@....de>
To:	Jason Cooper <jason@...edaemon.net>
CC:	Greg KH <gregkh@...uxfoundation.org>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Andrew Lunn <andrew@...n.ch>, Arnd Bergmann <arnd@...db.de>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	linux-kernel@...r.kernel.org, Michal Hocko <mhocko@...e.cz>,
	linux-mm@...ck.org, Kyungmin Park <kyungmin.park@...sung.com>,
	Mel Gorman <mgorman@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	linaro-mm-sig@...ts.linaro.org,
	linux-arm-kernel@...ts.infradead.org,
	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
Subject: Re: [PATCH v2] mm: dmapool: use provided gfp flags for all dma_alloc_coherent()
 calls

On 16.01.2013 18:47, Jason Cooper wrote:
> On Wed, Jan 16, 2013 at 06:32:09PM +0100, Soeren Moch wrote:
>> On 16.01.2013 09:55, Soeren Moch wrote:
>>> On 16.01.2013 04:24, Soeren Moch wrote:
>>>> I did not bisect it, but Marek mentioned earlier that commit
>>>> e9da6e9905e639b0f842a244bc770b48ad0523e9 in Linux v3.6-rc1 introduced
>>>> new code for dma allocations. This is probably the root cause for the
>>>> new (mis-)behavior (due to my tests 3.6.0 is not working anymore).
>>>
>>> I don't want to say that Mareks patch is wrong, probably it triggers a
>>> bug somewhere else! (in em28xx?)
>>
>> The em28xx sticks are using isochronous usb transfers. Is there a
>> special handling for that?
>
> I'm looking at that now.  It looks like the em28xx wants (as a maximum)
> 655040 bytes (em28xx-core.c:1088).  There are 5 transfer buffers, with
> 64 max packets and 2047 max packet size (runtime reported max & 0x7ff).
>
> If it actually needs all of that, then the answer may be to just
> increase coherent_pool= when using that driver.  I'll keep digging.

I already tested with 4M coherent pool size and could not see
significant improvement. Would it make sense to further increase the
buffer size?

Regards,
Soeren



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