tcptrace is your friend. One possibility is that your TCP windows are too small.
On Thu, 2006-05-18 at 15:03 -0700, David Kewley wrote: > On Tuesday 16 May 2006 23:44, Jeff Johnson wrote: > > Packet drop example: (other nodes post similar numbers) > > RX packets:1843133 errors:0 dropped:1245 overruns:0 frame:0 > > TX packets:1764828 errors:0 dropped:0 overruns:0 carrier:0 > > Question is: Where do these drops occur? > > I've not looked into it in detail right now, but I will suggest to you that > this "dropped" statistic may represent packets that the kernel successfully > received and delivered to the application's socket receive buffer, but the > application did not remove these packets from the buffer before the buffer > overran. At least, I've seen this behavior in other circumstances. > > The "Recv-Q" and "Send-Q" columns in the output of netstat show you the > current size of data in the socket receive & send buffers. I don't know if > there's a better way to keep an eagle eye on a particular socket's buffer > used sizes. > > Adding lines something like the following to /etc/sysctl.conf may help you, > so long as the application is fundamentally able to keep up with the > average flow rate, and just needs a little help to get by brief periods of > high flow or longer packet pickup latency: > > # Increase network write buffer max size from the default 128k to 512k > net.core.rmem_default = 524287 > net.core.rmem_max = 1048575 > net.core.wmem_default = 524287 > net.core.wmem_max = 1048575 > > # Increase TCP write buffer max size from the default 128k to 512k > net.ipv4.tcp_wmem = "4096 16384 524288" > > Of course in your case we're concerned about the rmem values, not so much > about the wmem values. > > David > _______________________________________________ > Beowulf mailing list, [email protected] > To change your subscription (digest mode or unsubscribe) visit > http://www.beowulf.org/mailman/listinfo/beowulf > _______________________________________________ Beowulf mailing list, [email protected] To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
