netdev - Re: [PATCH 00/10] Implement batching skb API

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Date:	Fri, 20 Jul 2007 13:17:40 +0530
From:	Krishna Kumar2 <krkumar2@...ibm.com>
To:	Stephen Hemminger <shemminger@...ux-foundation.org>
Cc:	davem@...emloft.net, gaagaan@...il.com,
	general@...ts.openfabrics.org, hadi@...erus.ca,
	herbert@...dor.apana.org.au, jagana@...ibm.com, jeff@...zik.org,
	johnpol@....mipt.ru, kaber@...sh.net, kumarkr@...ux.ibm.com,
	mcarlson@...adcom.com, mchan@...adcom.com, netdev@...r.kernel.org,
	peter.p.waskiewicz.jr@...el.com, rdreier@...co.com,
	rick.jones2@...com, Robert.Olsson@...a.slu.se, sri@...ibm.com,
	tgraf@...g.ch, xma@...ibm.com
Subject: Re: [PATCH 00/10] Implement batching skb API

Stephen Hemminger <shemminger@...ux-foundation.org> wrote on 07/20/2007
12:48:48 PM:

> You may see worse performance with batching in the real world when
> running over WAN's.  Like TSO, batching will generate back to back packet
> trains that are subject to multi-packet synchronized loss. The problem is
that
> intermediate router queues are often close to full, and when a long
string
> of packets arrives back to back only the first ones will get in, the rest
> get dropped.  Normal sends have at least minimal pacing so they are less
> likely do get synchronized drop.

Also forgot to mention in the previous mail, if performance is seen to be
dipping,
batching can be disabled on WAN's by:

echo 0 > /sys/class/net/<dev>/tx_batch_skbs

and use batching on local/site networks in that case.

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