Date: Wed, 11 Jul 2001 15:33:24 -0500 (CDT) From: Mike Silbersack <silby@silby.com> To: Martin Karsten <Martin.Karsten@KOM.tu-darmstadt.de> Cc: <freebsd-net@freebsd.org>, <oscar@ac.upc.es> Subject: Re: UDP packet loss on FreeBSD 4.x Message-ID: <20010711153113.L2408-100000@achilles.silby.com> In-Reply-To: <200107111512.RAA30280@KOM.tu-darmstadt.de>
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On Wed, 11 Jul 2001, Martin Karsten wrote: > Greetings, > > I have observed the following behaviour on FreeBSD 4.x platforms (4.0 till > 4.3 seem to be affected). > > When receiving a sufficiently fast stream of UDP packets (the borderline > seems to be around 3,500 packets/sec for e.g. the 'xl' driver on a 450MHz > Pentium), an application on the receiving host does not receive all packets > anymore, depending on which nic driver is used. A fraction of the lost > packets is reported in net.inet.ip.intr_queue_drops, but not all. > > Tests have shown that the losses occur for the 'xl' or 'ti' drivers, whereas > the 'fxp' and 'de' driver don't seem to be affected. Check the output of netstat -m after doing the test. I know that the xl driver puts all incoming packets into mbuf clusters, while the dc driver goes straight into mbufs if possible. That might not explain a slowdown in overall throughput, but it does mean that dc cards have a 4x larger incoming packet queue than xl cards. Back to netstat -m. If you see that your peak number of clusters is hitting the max, that's partially your answer, and upping the # of mbuf clusters could help. Mike "Silby" Silbersack To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-net" in the body of the message
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