My wish list for 6.1

[Martin Cracauer]

Kris Kennaway wrote on Sat, Dec 17, 2005 at 03:01:09AM -0500: 
> On Fri, Dec 16, 2005 at 10:34:09PM -0800, Avleen Vig wrote:
> > On Fri, Dec 16, 2005 at 10:40:22AM -0500, Martin Cracauer wrote:
> > > > 2.  SMP kernels for install.  Right now we only install a UP kernel, for
> > > > performance reasons.  We should be able to package both a UP and SMP
> > > > kernel into the release bits, and have sysinstall install both.  It 
> > > > should also select the correct one for the target system and make that
> > > > the default on boot.
> > > 
> > > If people are concerned about performance, I benchmarked a 6-beta
> > > kernel SMP versus UP on a socket 939 Opteron.
> > 
> > If those results are accurate, there's no real reason not to just use an
> > SMP kernel on default install?
> 
> Just because it didn't manifest on this workload, doesn't mean it
> doesn't on others.  I think this is the point :)

I tried to model different worklods.  The parallel part of my
benchmark suite has CPU-heavy processes, short plain http, php, long
plain http and mixtures thereof.

None of these showed the SMP kernel to be an overall disadvantage on a
one-processor system.

However, the tradeoffs are different.  The SMP kernel further
increases the tendency that FreeBSD had all along to give CPU eaters
more resources, disk and network I/O less, compared to Linux.

Whether this is good or bad is open for discussion.  From a traffic
control standpoint you can both argue that it is better to get the CPU
demands out of the way instead of getting more I/O done only to have
the I/Oing processes then pile up in the already overcrowded
CPU-demanding corner - and you can argue that you should get I/O done
ASAP so that the I/O-initiating process doesn't hang around
neccessaryily long.

This is for both schedulers.  I don't think this tendency is directly
caused by the scheduler, it is probably the I/O subsystems coercing
the scheduler, not the other way round.

Martin
-- 
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Martin Cracauer <cracauer at cons.org>   http://www.cons.org/cracauer/
FreeBSD - where you want to go, today.      http://www.freebsd.org/