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

Trond Myklebust
2008-12-16T13:02:51Z

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