netdev - Re: [PATCH 0/10 REV5] Implement skb batching and support in IPoIB/E1000

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Date:	Mon, 17 Sep 2007 08:51:40 -0400
From:	jamal <hadi@...erus.ca>
To:	David Miller <davem@...emloft.net>
Cc:	johnpol@....mipt.ru, herbert@...dor.apana.org.au, kaber@...sh.net,
	shemminger@...ux-foundation.org, jagana@...ibm.com,
	Robert.Olsson@...a.slu.se, rick.jones2@...com, xma@...ibm.com,
	gaagaan@...il.com, netdev@...r.kernel.org, rdreier@...co.com,
	peter.p.waskiewicz.jr@...el.com, mcarlson@...adcom.com,
	mchan@...adcom.com, general@...ts.openfabrics.org,
	kumarkr@...ux.ibm.com, tgraf@...g.ch, randy.dunlap@...cle.com,
	sri@...ibm.com
Subject: Re: [PATCH 0/10 REV5] Implement skb batching and support in
	IPoIB/E1000

On Sun, 2007-16-09 at 20:13 -0700, David Miller wrote:

> What Herbert and I want to do is basically turn on TSO for
> devices that can't do it in hardware, and rely upon the GSO
> framework to do the segmenting in software right before we
> hit the device.

Sensible. 

> This only makes sense for devices which can 1) scatter-gather
> and 2) checksum on transmit.  

If you have knowledge there are enough descriptors in the driver to
cover all skbs you are passing, do you need to have #1? 
Note i dont touch fragments, i am assuming the driver is smart enough to
handle them otherwise it wont advertise it can handle scatter-gather

> Otherwise we make too many copies and/or passes over the data.

I didnt understand this last bit - you are still going to go over the
list regardless of whether you call ->hard_start_xmit() once or
multiple times over the same list, no? In the later case i am assuming
a trimmed down ->hard_start_xmit()

> UDP is too easy a test case in fact :-)

I learnt a lot about the behavior out of doing udp (and before that with
pktgen); theres a lot of driver habits that may need to be tuned before
batching becomes really effective - which is easier to see with udp than
with tcp.

cheers,
jamal

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