linux-kernel - Re: problems with e1000 and jumboframes

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Message-ID: <20060805095846.GA17867@2ka.mipt.ru>
Date:	Sat, 5 Aug 2006 13:58:46 +0400
From:	Evgeniy Polyakov <johnpol@....mipt.ru>
To:	Jesse Brandeburg <jesse.brandeburg@...il.com>
Cc:	Chris Leech <chris.leech@...il.com>,
	Herbert Xu <herbert@...dor.apana.org.au>, arnd@...dnet.de,
	olel@....pl, linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: problems with e1000 and jumboframes

On Fri, Aug 04, 2006 at 02:02:51PM -0700, Jesse Brandeburg (jesse.brandeburg@...il.com) wrote:
> >> So how many skb allocation schemes do you code into a single driver?
> >> Kmalloc everything, page alloc everything, combination of kmalloc and
> >> page buffers for hardware that does header split?  That's three
> >> versions of the drivers receive processing and skb allocation that
> >> need to be maintained.
> >
> >At least try to create scheme which will not end up in 32k allocation in
> >atomic context. Generally I would recommend to use frag_list as much as
> >possible (or you can reuse skb list).
> 
> this is exactly what we ran into, you can't use skb list because the
> ip fragmentation reassembly code overwrites it.  If someone is feeling
> particularly miffed by this i would love to see a patch that used
> alloc_page() for all of our receive buffers for the legacy receive
> path (e1000_clean_rx_irq) then we would be able to use nr_frags and
> frag_list for receives.
> 
> Oh, except that eth_type_trans can't handle the entire packet in the
> frag_list (it wants the header in the skb->data)

Yes, part of the packet must live in skb->data, but it does not differ
from frag_list management - place part of the data in skb->data and the
rest into frag_list.
If you can create several skbs and link them togeter you defenitely can
organize pages into frag_list, just get pages from different skb->data
and free those skbs.

> anyway, this is not as easy a problem to solve as it would seem on the 
> surface.

No one says it is easy or not, but I'me 100% sure that 32k allocation
for 9k jumbo frame in atomic context is not what people expect from
high-performance NIC.

> Jesse
> -
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-- 
	Evgeniy Polyakov
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