[Lustre-discuss] Lustre clients: SLERT 10 support ?

[Andreas Dilger]

On May 29, 2008  12:35 -0400, Brian J. Murrell wrote:
> On Thu, 2008-05-29 at 18:24 +0200, Ralph Krotz wrote:
> > when trying to build the lustre client kernel modules configure aborts with 
> > the message "configure: error: Lustre does not support kernels with preempt 
> > enabled."
> > 
> > I'm using kernel 2.6.22.19-0.12-rt with CONFIG_PREEMPT_RT as provided by
> > SLERT 10.
> > 
> > Is there a quick solution to this issue ?

The "quick" solution is to just remove this configure check from
build/autoconf/lustre-build-linux.m4.

> Not really.  Maybe somebody with more knowledge about why we don't like
> CONFIG_PREEMPT_RT on the client can explain, but as far as addressing
> your failure directly, the only option would be to disable
> CONFIG_PREEMPT_RT and rebuild your client kernel.  Presumably this would
> conflict with your use of the -rt SLERT kernel though.

There were problems with PREEMPT in the past, but I don't know if they
were resolved or not as we test without this feature enabled.  I seem
to recall an issue with performance loss on HPC computing jobs due to
PREEMPT being enabled, but I don't recall the details.

If you are running in a non-production environment (i.e. terrible
things will not happen if client hangs), then I'd suggest to run
with PREEMPT enabled and see where it gets you.  Please feed back
any experience you have.

I've been running with PREEMPT enabled on my home test cluster for some
time without ill effects, but it doesn't get a very high load so it
may not expose the kind of problems that might be seen under heavy load.

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.