netdev - Re: [PATCH v2] tcp: splice as many packets as possible at once

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Date:	Wed, 4 Feb 2009 11:12:01 +0300
From:	Evgeniy Polyakov <zbr@...emap.net>
To:	Willy Tarreau <w@....eu>
Cc:	David Miller <davem@...emloft.net>, herbert@...dor.apana.org.au,
	jarkao2@...il.com, dada1@...mosbay.com, ben@...s.com,
	mingo@...e.hu, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, jens.axboe@...cle.com
Subject: Re: [PATCH v2] tcp: splice as many packets as possible at once

On Wed, Feb 04, 2009 at 07:19:47AM +0100, Willy Tarreau (w@....eu) wrote:
> Yes myri10ge for the optimal 4080, but with e1000 too (though I don't
> remember the exact optimal value, I think it was slightly lower).

Very likely it is related to the allocator - the same allocation
overhead to get a page, but 2.5 times bigger frame.

> For the myri10ge, could this be caused by the cache footprint then ?
> I can also retry with various values between 4 and 9k, including
> values close to 8k. Maybe the fact that 4k is better than 9 is
> because we get better filling of all pages ?
> 
> I also remember having used a 7 kB MTU on e1000 and dl2k in the past.
> BTW, 7k MTU on my NFS server which uses e1000 definitely stopped the
> allocation failures which were polluting the logs, so it's been running
> with that setting for years now.

Recent e1000 (e1000e) uses fragments, so it does not suffer from the
high-order allocation failures.

-- 
	Evgeniy Polyakov
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