netdev - [2.6.30.1] Significant latency playing video file from NFS4 share

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Message-Id: <200907172250.51504.elendil@planet.nl>
Date:	Fri, 17 Jul 2009 22:50:50 +0200
From:	Frans Pop <elendil@...net.nl>
To:	linux-nfs@...r.kernel.org
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	netdev@...r.kernel.org
Subject: [2.6.30.1] Significant latency playing video file from NFS4 share

While playing a video (avi) file from an nfs4 share using vlc I'm getting 
significant latencies on the client resulting in video skips every 10-30 
seconds. latencytop gives me for example:

Cause                                      Maximum     Percentage
rpc_wait_bit_killable __rpc_execute
   rpc_execute rp[...]                 2638.5 msec         46.1 %
Scheduler: waiting for cpu               25.1 msec         19.9 %
Waiting for event (select)                5.0 msec         23.0 %
Waiting for event (poll)                  4.8 msec          0.3 %
Userspace lock contention                 4.6 msec          9.9 %
Waiting for data on unix socket           1.7 msec          0.8 %

Process vlc (6681)              Total: 2790.2 msec
rpc_wait_bit_killable __rpc_execute
   rpc_execute rp[...]                 2638.5 msec         94.6 % [1]
Scheduler: waiting for cpu                9.3 msec          1.5 %
Waiting for event (poll)                  4.8 msec          0.6 %
Userspace lock contention                 4.3 msec          3.3 %
Waiting for event (select)                0.6 msec          0.1 %

[1] nfs4_proc_getattr nfs4_proc_getattr __nfs_revalidate_inode nfs_getattr 
vfs_geta[...]

There is no other NFS access going on at the time; just reading the single 
file. No significant other processes running on either the client or the 
server. latencytop on the server does not show any significant latencies.

Both server and client are dual core x86_64 running 2.6.30.1 with 
identical configs (attached); Debian stable.

From /etc/exports on the server:
/srv/exports            10.19.66.0/24(rw,fsid=0,subtree_check,sync)
/srv/exports/myshare    10.19.66.0/24(rw,subtree_check,sync,mp,nohide)

mount on the client:
elrond:/myshare on /srv/<mountpoint> type nfs4 (rw,addr=10.19.66.2)

Cheers,
FJP


View attachment "config-2.6.30.1" of type "text/plain" (68250 bytes)