linux-kernel - Re: problems with e1000 and jumboframes

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Message-id: <44D21845.6020703@arndnet.de>
Date:	Thu, 03 Aug 2006 17:37:41 +0200
From:	Arnd Hannemann <arnd@...dnet.de>
To:	Evgeniy Polyakov <johnpol@....mipt.ru>
Cc:	Krzysztof Oledzki <olel@....pl>, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: problems with e1000 and jumboframes


Evgeniy Polyakov wrote:
> On Thu, Aug 03, 2006 at 05:08:51PM +0200, Krzysztof Oledzki (olel@....pl) wrote:
>>>> Why? After your explanation that makes sense for me. The driver needs
>>>> one contiguous chunk for those 9k packet buffer and thus requests a
>>>> 3-order page of 16k. Or do i still do not understand this?
>>> Correct, except that it wants 32k.
>>> e1000 logic is following:
>>> align frame size to power-of-two,
>> 16K?
> 
> Yep.
> 
>>> then skb_alloc adds a little
>>> (sizeof(struct skb_shared_info)) at the end, and this ends up
>>> in 32k request just for 9k jumbo frame.
>> Strange, why this skb_shared_info cannon be added before first alignment? 
>> And what about smaller frames like 1500, does this driver behave similar 
>> (first align then add)?
> 
> It can be.
> Could attached  (completely untested) patch help?

I will try this in a minute. However is there any way to see which
allocation e1000 does without triggering allocation failures? ;-)

Thanks,
Arnd Hannemann


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