Re: High load in 2.6.27, NFS / rpcauth_lookup_credcache()?

Willy Tarreau
2008-12-16T21:22:48Z

On Tue, Dec 16, 2008 at 08:02:33AM -0500, Trond Myklebust wrote:
> On Mon, 2008-12-15 at 15:44 -0800, Harry Edmon wrote:
> > Trond Myklebust wrote:
> > > On Thu, 2008-10-23 at 14:36 +0200, Max Kellermann wrote:
> > >
> > >> On 2008/10/22 11:12, Max Kellermann <max@duempel.org> wrote:
> > >>
> > >>> 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?
> > >>>
> > >> I have bisected the problem: 98a8e323 is the result ("SUNRPC: Add a
> > >> helper rpcauth_lookup_generic_cred()"). 5c691044 is ok.
> > >>
> > >> See the attached oprofile annotation data for both commits. I guess
> > >> that the function rpcauth_lookup_credcache() is waiting for a spinlock
> > >> too often and too long. Trond, any idea?
> > >>
> > >
> > > Can you add a '-v' to the rpc.gssd daemon startup line? I'd like to see
> > > how often you are creating new gss contexts.
> > >
> > >
> > >> Harry: added you to Cc because your problem sounds similar.
> > >>
> > >
> > > Harry's problem is should be unrelated. afaik, he is seeing a problem
> > > with userland RPC code, not kernel rpc code.
> > >
> > > Trond
> > >
> > >
> > I am finally getting some time to look at my problem that I originally
> > reported in October (SUNRPC problem with 2.6.26 and beyond), and I am
> > seeing the same behavior as Max Kellermann when my machine slows as I
> > described earlier. The system in question is currently running
> > 2.6.27.7. Here is what I see when it is misbehaving:
> >
> > samples % image name app name
> > symbol name
> > 11380517 57.4191 sunrpc.ko sunrpc
> > rpcauth_lookup_credcache
> > 3263657 16.4664 sunrpc.ko sunrpc
> > generic_match
> > 1081287 5.4555 vmlinux vmlinux
> > copy_user_generic_string
> > 499407 2.5197 vmlinux vmlinux
> > __posix_lock_file
> > [...]
> >
> > And here is what I see when I stop the programs that are chewing up all
> > the system time, and then starting them up again:
> >
> > samples % image name app name
> > symbol name
> > 6372650 21.7978 vmlinux vmlinux
> > copy_user_generic_string
> > 5401386 18.4755 sunrpc.ko sunrpc
> > rpcauth_lookup_credcache
> > 3018753 10.3257 vmlinux vmlinux
> > __posix_lock_file
> > 1050095 3.5919 sunrpc.ko sunrpc
> > generic_match
> >
> >
> > and I am not using Kerberos with NFSv4 (i.e. no rpc.gssd). Did you ever
> > find a solution for this problem with rpcauth_lookup_credcache?
>
> http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git&a=commitdiff&h=23918b03060f6e572168fdde1798a905679d2e06

Trond, this should be included into next stable, right ?

It's fortunate because I know someone else who recently described me the
same problem under the same circumstances when migrating from 2.6.22 to
2.6.27.

Regards,
Willy