Date: Fri, 4 Oct 2002 11:34:46 -0700 (PDT) From: Matthew Dillon <dillon@apollo.backplane.com> To: Alexander Leidinger <Alexander@Leidinger.net> Cc: current@FreeBSD.ORG Subject: Re: Meaning of net.inet.tcp.inflight_debug output? Message-ID: <200210041834.g94IYkBR003033@apollo.backplane.com> References: <20021004135022.3decb56f.Alexander@Leidinger.net>
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:Hi, : :what does this mean? Is it important? :---snip--- :kernel: 0xc27b4814 bw 4 rttbest 2735 srtt 2250 bwnd 2803 :kernel: 0xc0ef235c bw 23101 rttbest 680 srtt 293056 bwnd 1063153 :kernel: 0xc27b435c bw 54061 rttbest 1297 srtt 1756 bwnd 28636 :kernel: 0xc27b435c bw 47663 rttbest 1297 srtt 1784 bwnd 25793 :kernel: 0xc0ef235c bw 24288 rttbest 680 srtt 305216 bwnd 1163779 :kernel: 0xc0ef235c bw 22928 rttbest 680 srtt 306864 bwnd 1104680 :kernel: 0xc0ef235c bw 19812 rttbest 680 srtt 311471 bwnd 969203 :kernel: 0xc27b435c bw 53468 rttbest 1297 srtt 2014 bwnd 30508 :kernel: 0xc27b435c bw 47727 rttbest 1297 srtt 1767 bwnd 25705 :---snip--- : :Bye, :Alexander. : :http://www.Leidinger.net Alexander @ Leidinger.net : GPG fingerprint = C518 BC70 E67F 143F BE91 3365 79E2 9C60 B006 3FE7 When you turn the debugging on it will print out various parameters used to calculate the bandwidth window. The higher the debug value, the more often it prints out the stats (assuming a TCP is under load). Since the stats may reflect any tcp connection you typically only do this while running a single TCP connection under heavy load. bw: Calculated bandwidth of connection, bytes/sec. Note that if the only connection is you typing in a shell then the 'bw' you get will be the approximate data rate created by your typing. rttbest: The best RTT observed for the connection to date srtt: The current smoothed round trip time bwnd: The calculated bandwidth window ( which is used to limit the amount of unacknowledged data being transmitted to the bandwidth delay product of the connection ). rttbest and srtt are scaled to hz * 32, I believe (I'm not positive). So with the default 100 hz it would be scaled to 3200, so an rttbest of 680 would translate to 212mS. Sounds like a connection over a modem. The bandwidth delay product calculation is used to limit the size of the transmit window... that is, the number of data packets that can be inflight (on the wire) without being acknowledged. This is of particular use over a modem connection (prevents too many packets from building up in the send queue) or a GigE link (prevents the interface queue from being completely blown out of the water and dropping packets when large TCP buffers have been configured, amoung other things). -Matt Matthew Dillon <dillon@backplane.com> To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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