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

Harry Edmon
2008-12-15T23:57:31Z

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?

--

Dr. Harry Edmon E-MAIL: harry@atmos.washington.edu
206-543-0547 harry@washington.edu
Dept of Atmospheric Sciences FAX: 206-543-0308
University of Washington, Box 351640, Seattle, WA 98195-1640