Re: Large file copy to NFS mounted directory causes delay in other application packets

[Manavalan Krishnan <manavalan_k@yahoo.com>]

(1) NFS is using TCP
(2) yes eth0 is dedicated to heartbeat and eth1 is dedicated to NFS
(3) I notice the following at the system where file copy is occuring

The kernel Recv-Q of the heartbeat application socket grows but not delivered to the socket recv call. 
Here is the netstat output.

Proto  Recv-Q  Send-Q   Local Address         Foreign Address

udp    11522                0  *:23435                     *:*

As soon as I stop the file transfer, the socket recv call receives the packets and Recv-Q goes 0.
(4) The server has 4 cpu cores and 25G RAM

________________________________
From: Eric Dumazet <eric.dumazet@gmail.com>
To: Manavalan Krishnan <manavalan_k@yahoo.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>; netdev <netdev@vger.kernel.org>
Sent: Tuesday, November 8, 2011 10:24 PM
Subject: Re: Large file copy to NFS mounted directory causes delay in other application packets

Le mardi 08 novembre 2011 à 21:28 -0800, Manavalan Krishnan a écrit :
> Hi All
> 
> I have two systems with two network interfaces each(eth0 and eth1). I
> am running linux-HA (heartbeat deamon) on both the systems and they
> use eth0 for exchanging heartbeats. I have NFS mounted directory in
> one system and the NFS client uses the interface eth1. 
> 
> I try to copy a large file to NFS mounted directory. But the heartbeat
> daemons misses the heartbeat packets from peers while copy is under
> progress. I did tcpdump and found that the heartbeat packets are
> delayed for few seconds before sent out on eth0. When I stop the file
> copy, the heartbeats are delivered properly. It seems linux kernel
> somehow giving priority for NFS packets(generated from the file copy)
> over other application packets.
> 
> Any thoughts on this behavior? Is there any way we can avoid this so
> that application packets get equal chance while large file copy to NFS
> mounted directory under progress?
> 
CC netdev

1) Is your NFS using UDP or TCP ?
2) Is your eth0 dedicated to heartbeats and eth1 to NFS traffic ?
3) How do you know heartbeats are delayed ?
4) Is your server CPU bounded ?

Thanks


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