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Date: Sun, 30 Mar 2008 06:43:44 +0100 From: Deomid Ryabkov <myself@...er.pp.ru> To: linux-kernel@...r.kernel.org Subject: Send-Q on UDP socket growing steadily - why? This has started recently and i'm at a loss as to why. Send-Q on a moderately active UDP socket keeps growing steadily until it reaches ~128K (wmem_max?) at which point socket writes start failing. The application in question is standard ntpd from Fedora 7, kernel is the latest available for the distro, that is 2.6.23.15-80.fc7 #1 SMP Sun Feb 10 16:52:18 EST 2008 x86_64 BIND, running on the same machine, does not exhibit this problem, but that may be because it does not get nearly as much load as ntpd, which is part of the pool.ntp.org. That said, load is really not very high, on the order of 10 QPS, and machine is 99+% idle. ntpd seems to be doing its usual select-recvmsg-sendto routine, nothing out of the ordinary. And yet, Send-Q keeps growing at _exactly_ 360 bytes every 10 seconds, here's a sample of output shortly after ntpd restart: # while sleep 1; do netstat -na | grep 177:123; done udp 0 17280 89.111.168.177:123 0.0.0.0:* udp 0 17280 89.111.168.177:123 0.0.0.0:* udp 0 17280 89.111.168.177:123 0.0.0.0:* udp 0 17280 89.111.168.177:123 0.0.0.0:* udp 0 17280 89.111.168.177:123 0.0.0.0:* udp 0 17280 89.111.168.177:123 0.0.0.0:* udp 0 17280 89.111.168.177:123 0.0.0.0:* udp 0 17280 89.111.168.177:123 0.0.0.0:* -------> +360 bytes udp 0 17640 89.111.168.177:123 0.0.0.0:* udp 0 17640 89.111.168.177:123 0.0.0.0:* udp 0 17640 89.111.168.177:123 0.0.0.0:* udp 0 17640 89.111.168.177:123 0.0.0.0:* udp 0 17640 89.111.168.177:123 0.0.0.0:* udp 0 17640 89.111.168.177:123 0.0.0.0:* udp 0 17640 89.111.168.177:123 0.0.0.0:* udp 0 17640 89.111.168.177:123 0.0.0.0:* udp 0 17640 89.111.168.177:123 0.0.0.0:* udp 0 17640 89.111.168.177:123 0.0.0.0:* -------> +360 bytes, 10 seconds later udp 0 18000 89.111.168.177:123 0.0.0.0:* udp 0 18000 89.111.168.177:123 0.0.0.0:* udp 0 18000 89.111.168.177:123 0.0.0.0:* udp 0 18000 89.111.168.177:123 0.0.0.0:* udp 0 18000 89.111.168.177:123 0.0.0.0:* udp 0 18000 89.111.168.177:123 0.0.0.0:* udp 0 18000 89.111.168.177:123 0.0.0.0:* udp 0 18000 89.111.168.177:123 0.0.0.0:* udp 0 18000 89.111.168.177:123 0.0.0.0:* udp 0 18000 89.111.168.177:123 0.0.0.0:* -------> +360 bytes, 10 seconds later udp 0 18360 89.111.168.177:123 0.0.0.0:* [...] etc, etc. My understanding is that non-empty send queue for UDP sockets should be very rare occurence, maybe under extreme loads. And then there's this steady creep... What's going on? It almost looks like something is leaking somewhere. -- Deomid Ryabkov aka Rojer myself@...er.pp.ru rojer@...admins.ru ICQ: 8025844 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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