netdev - Re: [RFC] tcp: use order-3 pages in tcp

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Date:	Sun, 23 Sep 2012 20:13:54 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jan Engelhardt <jengelh@...i.de>
Cc:	David Miller <davem@...emloft.net>, rick.jones2@...com,
	subramanian.vijay@...il.com, netdev@...r.kernel.org
Subject: Re: [RFC] tcp: use order-3 pages in tcp_sendmsg()

On Sun, 2012-09-23 at 19:40 +0200, Jan Engelhardt wrote:

> 
> Cache sizes, and an oddity.
> 
> L1 cache sizes have not increased ever since (the 2011 Intel i7-2600
> has the same amount of L1 as a 1998ish AMD K6-2), and the Atom N450
> even has less, namely 24d+32i, meaning a 13000ish MTU might be more
> accurate for netbooks of this kind.
> 

MTU above 64K is not really useful, at least for IPv4, I think.

> What would a MTU of 64K buy? Offloading seems pointless for the lo
> device. There is no hardware to offload it to - well, the
> machine already has the packet too.

It buys 25% increase of performance. Not too bad...

I yet have to make sure no adjustment is needed, in TCP stack for
example.

If you try to change lo mtu on an old kernel (eg 2.6.38, on my laptop),
you can notice some packets drops (TCPBacklogDrop)


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