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

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Date:	Wed, 09 Nov 2011 09:59:09 +0100
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>
Subject: Re: Large file copy to NFS mounted directory causes delay in other
 application packets

Please dont top post on these lists, thanks.

Le mercredi 09 novembre 2011 à 00:13 -0800, Manavalan Krishnan a écrit :
> (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                     *:*
> 

OK so the sending side is OK : The delay is at receiver side.

Note that since netstat shows receive queue has some skbs, it should be
available to heartbeat daemon immediately.

> 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
> 

1) How many nfsd threads are running ?
   grep th /proc/net/rpc/nfsd

2) WHat kind of NIC do you use ?
   lsmod , lspci

3) Hmm, are IRQ to eth0/eth1 handled by same cpu ?
  grep eth /proc/interrupts

4) You could try to cpu affine all nfsd to cpu0,cpu1,cpu2  and heartbeat
daemon to cpu3.
   man taskset

5) You could 'strace -ttt' heartbeat daemon to check if it is not
blocked on some local disk access (it competes with all nfsd threads)



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