Re: [PATCH V2 1/4] arm: mvebu: increase atomic coherent pool sizefor armada 370/XP

[Sören Moch]

>>> For Armada 370/XP we have the same problem that for the commit
>>> cb01b63, so we applied the same solution: "The default 256 KiB
>>> coherent pool may be too small for some of the Kirkwood devices, so
>>> increase it to make sure that devices will be able to allocate their
>>> buffers with GFP_ATOMIC flag"
>>
>> I see a regression from linux-3.5 to linux-3.6 and think there might
>> be a fundamental problem
>> with this patch. On my Kirkwood system (guruplug server plus) with
>> linux-3.6.2 I see following
>> errors and corresponding malfunction even with further increased
>> (2M, 4M) pool size:
>>
>> Oct 19 00:41:22 guru kernel: ERROR: 4096 KiB atomic DMA coherent
>> pool is too small!
>> Oct 19 00:41:22 guru kernel: Please increase it with coherent_pool=
>> kernel parameter!
>>
>> So I had to downgrade to linux-3.5 which is running without problems.
>>
>> I use SATA and several DVB sticks (em28xx / drxk and dib0700).
>
> I'm guess its the DVB sticks which are causing the problems. We have a
> number of kirkwood devices with two SATA devices which had problems
> until we extended the coherent_pool. The DVB sticks are probably take
> more coherent RAM. There was also an issue found recently:
>
> http://www.spinics.net/lists/arm-kernel/msg203962.html
>
> That conversation has gone quiet, but that could be because the
> participants are at ELCE.
>
>          Andrew

OK, I hope this GFP flag correction will help.

Could there be a fragmentation problem in the coherent_pool with the
different drivers running under heavy load?
With a pool size of 1M I see this error after several minutes, with a 4M
pool I see this error after several 10 minutes. Difficult to test, but not
acceptable on a production system.

Soeren
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