linux-kernel - High load in 2.6.27, NFS / rpcauth_lookup

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Date:	Wed, 22 Oct 2008 11:12:08 +0200
From:	Max Kellermann <max@...mpel.org>
To:	linux-kernel@...r.kernel.org, linux-nfs@...r.kernel.org
Subject: High load in 2.6.27, NFS / rpcauth_lookup_credcache()?

Hi,

after I was able to fix http://lkml.org/lkml/2008/10/17/147, the
server which was already upgraded to 2.6.27.2 still gets very high
load.  It is a web server with NFS file storage (NetApp), and while
the others in the cluster (kernel 2.6.25) have a load of 1-3, 2.6.27.2
gets 30-50.

I did an oprofile, with the following results (server just started,
load "only" 5-10):

87593    56.1116  (no location information)   vmlinux
vmlinux                  rpcauth_lookup_credcache
16037    10.2732  auth_generic.c:0            vmlinux
vmlinux                  generic_match
6460      4.1382  (no location information)   php4
php4                     (no symbols)
2478      1.5874  (no location information)   libc-2.7.so
libc-2.7.so              (no symbols)
[...]

We havn't configured any special authentication method.  It is a NFSv3
over UDP mount, but the kernel has NFSv4 and therefore KRB5 enabled.

Any ideas why rpcauth_lookup_credcache() goes overboard with CPU
usage?

Max

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