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

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Date:	Thu, 23 Aug 2007 23:18:20 -0400
From:	Bill Fink <billfink@...dspring.com>
To:	Rick Jones <rick.jones2@...com>
Cc:	hadi@...erus.ca, David Miller <davem@...emloft.net>,
	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

On Thu, 23 Aug 2007, Rick Jones wrote:

> jamal wrote:
> > [TSO already passed - iirc, it has been
> > demostranted to really not add much to throughput (cant improve much
> > over closeness to wire speed) but improve CPU utilization].
> 
> In the one gig space sure, but in the 10 Gig space, TSO on/off does make a 
> difference for throughput.

Not too much.

TSO enabled:

[root@...g2 ~]# ethtool -k eth2
Offload parameters for eth2:
rx-checksumming: on
tx-checksumming: on
scatter-gather: on
tcp segmentation offload: on

[root@...g2 ~]# nuttcp -w10m 192.168.88.16
11813.4375 MB /  10.00 sec = 9906.1644 Mbps 99 %TX 80 %RX

TSO disabled:

[root@...g2 ~]# ethtool -K eth2 tso off
[root@...g2 ~]# ethtool -k eth2
Offload parameters for eth2:
rx-checksumming: on
tx-checksumming: on
scatter-gather: on
tcp segmentation offload: off

[root@...g2 ~]# nuttcp -w10m 192.168.88.16
11818.2500 MB /  10.00 sec = 9910.0176 Mbps 100 %TX 78 %RX

Pretty negligible difference it seems.

This is with a 2.6.20.7 kernel, Myricom 10-GigE NICs, and 9000 byte
jumbo frames, in a LAN environment.

For grins, I also did a couple of tests with an MSS of 1460 to
emulate a standard 1500 byte Ethernet MTU.

TSO enabled:

[root@...g2 ~]# ethtool -k eth2
Offload parameters for eth2:
rx-checksumming: on
tx-checksumming: on
scatter-gather: on
tcp segmentation offload: on

[root@...g2 ~]# nuttcp -M1460 -w10m 192.168.88.16
 5102.8503 MB /  10.06 sec = 4253.9124 Mbps 39 %TX 99 %RX

TSO disabled:

[root@...g2 ~]# ethtool -K eth2 tso off
[root@...g2 ~]# ethtool -k eth2
Offload parameters for eth2:
rx-checksumming: on
tx-checksumming: on
scatter-gather: on
tcp segmentation offload: off

[root@...g2 ~]# nuttcp -M1460 -w10m 192.168.88.16
 5399.5625 MB /  10.00 sec = 4527.9070 Mbps 99 %TX 76 %RX

Here you can see there is a major difference in the TX CPU utilization
(99 % with TSO disabled versus only 39 % with TSO enabled), although
the TSO disabled case was able to squeeze out a little extra performance
from its extra CPU utilization.  Interestingly, with TSO enabled, the
receiver actually consumed more CPU than with TSO disabled, so I guess
the receiver CPU saturation in that case (99 %) was what restricted
its performance somewhat (this was consistent across a few test runs).

						-Bill
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