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

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Date:	Sun, 23 Sep 2012 19:40:33 +0200 (CEST)
From:	Jan Engelhardt <jengelh@...i.de>
To:	David Miller <davem@...emloft.net>
cc:	eric.dumazet@...il.com, rick.jones2@...com,
	subramanian.vijay@...il.com, netdev@...r.kernel.org
Subject: Re: [RFC] tcp: use order-3 pages in tcp_sendmsg()


On Sunday 2012-09-23 18:16, David Miller wrote:
>> On Friday 2012-09-21 18:27, David Miller wrote:
>> 
>>>From: Eric Dumazet <eric.dumazet@...il.com>
>>>Date: Fri, 21 Sep 2012 17:48:31 +0200
>>>
>>>> There is probably a reason why lo default MTU is 16436 ?
>>>
>>>That's what fit into L1 caches back in 1999
>> 
>> Would it make sense to automatically set lo's MTU on device
>> registration to the actual size of the L1 that the $running system
>> has?
>
>I think a fixed value of 64K would be a easiest, because another issue
>is that back in 1999 we didn't have GRO/GSO/etc.


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.

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.
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