linux-kernel - Re: [2.6.35-rc3] select useful number of entries for DMA debugging...

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Date:	Sat, 10 Jul 2010 15:52:04 +0100
From:	Daniel J Blueman <daniel.blueman@...il.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [2.6.35-rc3] select useful number of entries for DMA debugging...

On 9 July 2010 22:33, Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> On Mon, Jul 5, 2010 at 1:35 AM, Daniel J Blueman
> <daniel.blueman@...il.com> wrote:
>> When booting 2.6.35-rc3 on some different x86 boxes with DMA debugging
>> enabled, I've consistently seen it exhaust the allocated entries during
>> boot, giving 'DMA-API: debugging out of memory - disabling'.
>>
>> Increase number of entries to allow DMA debugging again.
>
> Rather than increase the default that gets allocated whenever anybody
> enables the DMA debugging, I'd really prefer to see people use the
> kernel command line option if they run out. After all, it's a (pretty
> esoteric) debug option, and the number of required entries depends on
> machine configuration. I'd rather not make the default cover a huge
> number, when you could just add
>
>   dma_debug_entries=65536
>
> on the kernel boot command line instead for machines that want/need it..

That said, I am seeing the DMA pool exhaust on a single socket Core i5
system with Intel graphics and no other adapters - seems like a fairly
common case. If eg 25% of developers will be using similar to this,
maybe it's good to make DMA debugging less immediately esoteric?

On the other hand, I would immediately agree if the exhaustion
occurred on an atypical setup.
-- 
Daniel J Blueman
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