em0 performance subpar

[Mike Tancsa]

On 4/28/2011 3:29 AM, Adam Stylinski wrote:
> Hello,
> 
> I have an intel gigabit network adapter (the 1000 GT w/chipset 82541PI) which performs poorly in Freebsd compared to the same card in Linux.  I've tried this card in two different freebsd boxes and for whatever reason I get poor transmit performance.  I've done all of the tweaking specified in just about every guide out there (the usual TCP window scaling, larger nmbclusters, delayed acks, etc) and still I get only around 600mbps.  I'm using jumbo frames, with an MTU of 9000.  I'm testing this with iperf.  While I realize that this may not be the most realistic test, linux hosts with the same card can achieve 995Mbit/s to another host running this.  When the Freebsd box is the server, Linux hosts can transmit to it at around 800 something Mbit/s.  I've increased the transmit descriptors as specified in the if_em man page, and while that gave me 20 or 30 more mbit/s, my transmit performance is still below normal.  
> 
> sysctl stats report that the card is trigger a lot of tx_desc_fail2:
> 	dev.em.0.tx_desc_fail2: 3431

Try the tests using the tools in /usr/src/tools/tools/netperf to
generate / test udp traffic.

Perhaps give the driver from HEAD a try. There are a few fixes to it. I
back ported it to RELENG_8, but it should work on 8.2R as well.

http://www.tancsa.com/em-723.tgz

what does pciconf -lvc for your em NIC show ?
also, vmstat -i

	---Mike



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Mike Tancsa, tel +1 519 651 3400
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