Date: Mon, 16 Feb 2004 18:07:33 +0100 From: Marian Durkovic <md@bts.sk> To: freebsd-net@freebsd.org Subject: TX performance problems with 3Com 905C cards Message-ID: <20040216170733.GA37519@us.svf.stuba.sk>
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Hi all, I'm experiencing some performance issues with 3Com 905C cards @ FreeBSD 4.8 When running nttcp tests with other servers, the result is: otherbox -> box with 3c905 Bytes Real s CPU s Real-MBit/s CPU-MBit/s Calls Real-C/s CPU-C/s l409600000 34.80 2.96 94.1489 1105.1982 100000 2873.20 33728.0 1409600000 34.82 1.18 94.1175 2773.2828 281323 8080.27 238094.6 box with 3c905 -> otherbox Bytes Real s CPU s Real-MBit/s CPU-MBit/s Calls Real-C/s CPU-C/s l409600000 38.86 1.18 84.3323 2766.3223 282788 7277.88 238733.7 1409600000 38.85 1.56 84.3524 2100.2557 100000 2574.23 64094.7 The above data shows that 3c905C is able to receive data at full wire speed of FastEthernet since the value corresponds to its theoretical maximum. However, when 3c905C is transmitting data, the rate drops to 84 Mbps. TCPdump doesn't show any packet retransmissions or other problems, however, when 3c905C is sending data, the delay betwen the time when data packet is sent out and it's corresponding ACK increases significantly. With 128 KB TCPwindow, the ACKs are delivered 12 msec after the packet. With 256 KB TCPwindow, the ACKs are delivered 24 msec after the packet. I.e. regardless of TCPwindow size, the rate is limited to 84 Mbps. It looks like the ACKs are delivered to the kernel somehow delayed, in fact only when TCP stops sending data because the full TCPwindow of unacknowledged data is in transit. Seems like something works in half-duplex mode, although the card is connected to 100 Mbps fullduplex port and both the switch and ifconfig -a confirm 100baseTX full duplex. Is this a known hardware limitation of these cards? Is there something that needs to be tuned on the PCI bus? Or is there some problem in the xl driver, causing such delays or e.g. assuming half-duplex operation? Thanks in advance for your help. M. -------------------------------------------------------------------------- ---- ---- ---- Marian Durkovic network manager ---- ---- ---- ---- Slovak Technical University Tel: +421 2 524 51 301 ---- ---- Computer Centre, Nam. Slobody 17 Fax: +421 2 524 94 351 ---- ---- 812 43 Bratislava, Slovak Republic E-mail/sip: md@bts.sk ---- ---- ---- --------------------------------------------------------------------------
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