netdev - Re: [PATCH 0/9 Rev3] Implement batching skb API and support in IPoIB

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Date:	Mon, 27 Aug 2007 11:07:50 -0700
From:	Rick Jones <rick.jones2@...com>
To:	David Miller <davem@...emloft.net>
Cc:	jheffner@....edu, billfink@...dspring.com, hadi@...erus.ca,
	krkumar2@...ibm.com, gaagaan@...il.com,
	general@...ts.openfabrics.org, herbert@...dor.apana.org.au,
	jagana@...ibm.com, jeff@...zik.org, johnpol@....mipt.ru,
	kaber@...sh.net, mcarlson@...adcom.com, mchan@...adcom.com,
	netdev@...r.kernel.org, peter.p.waskiewicz.jr@...el.com,
	rdreier@...co.com, Robert.Olsson@...a.slu.se,
	shemminger@...ux-foundation.org, sri@...ibm.com, tgraf@...g.ch,
	xma@...ibm.com
Subject: Re: [PATCH 0/9 Rev3] Implement batching skb API and support in IPoIB

David Miller wrote:
> From: John Heffner <jheffner@....edu>
> Date: Sun, 26 Aug 2007 21:32:26 -0400
> 
> 
>>There are a few interesting things here.  For one, the bursts caused by 
>>TSO seem to be causing the receiver to do stretch acks.  This may have a 
>>negative impact on flow performance, but it's hard to say for sure how 
>>much.  Interestingly, it will even further reduce the CPU load on the 
>>sender, since it has to process fewer acks.
>>
>>As I suspected, in the non-TSO case the receiver gets lots of packets 
>>directly queued to user.  This should result in somewhat lower CPU 
>>utilization on the receiver.  I don't know if it can account for all the 
>>difference you see.
> 
> 
> I had completely forgotten these stretch ACK and ucopy issues.

ISTR that LRO will induce stretch ACKs as well.  Not that I dislike fewer ACKs 
mind you... :)

rick jones
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