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

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Date:	Wed, 9 Nov 2011 00:13:09 -0800 (PST)
From:	Manavalan Krishnan <manavalan_k@...oo.com>
To:	Eric Dumazet <eric.dumazet@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:	linux-kernel@...r.kernel.org, netdev <netdev@...r.kernel.org>
Subject: Re: Large file copy to NFS mounted directory causes delay in other application packets

(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@...il.com>
To: Manavalan Krishnan <manavalan_k@...oo.com>
Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>; netdev <netdev@...r.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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