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

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Date:	Fri, 14 Sep 2007 10:24:35 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	billfink@...dspring.com
Cc:	hadi@...erus.ca, jheffner@....edu, rick.jones2@...com,
	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

From: Bill Fink <billfink@...dspring.com>
Date: Fri, 14 Sep 2007 03:20:55 -0400

> TSO disabled performance is always better than equivalent TSO enabled
> performance.  With TSO enabled, the optimum performance is indeed at
> a TX/RX interrupt coalescing value of 75 usec.  With TSO disabled,
> performance is the full 10-GigE line rate of 9910 Mbps for any value
> of TX/RX interrupt coalescing from 15 usec to 105 usec.

Note that the systems where the coalescing tweaking if often necessary
are the heavily NUMA'd systems where cpu to device latency can be
huge, like the big SGI ones which is where we had to tweak things in
the tg3 driver in the first place.

On most systems, as you saw mostly in the non-TSO case, the
value choosen for the most part is arbitrary and not critical.
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