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
