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SubjectRe: [2.6.30.1] Significant latency playing video file from NFS4 share
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On Fri, 2009-07-17 at 22:50 +0200, Frans Pop wrote:
> 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

Have you tried running nfs-iostat from the nfs-utils package to try and
figure out what the latency is on each READ request from the client?

http://git.linux-nfs.org/?p=steved/nfs-utils.git;a=blob_plain;f=tools/nfs-iostat/nfs-iostat.py;hb=HEAD

You need to run something like

nfs-iostat --page 20 10 /src/<mountpoint>

while running the vlc app.

Trond



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