Apparent performance regression 8.3@ -> 8.4 at r255966?

[David Wolfskill]

On Mon, Oct 07, 2013 at 09:19:38PM +0200, Erik Cederstrand wrote:
> ... 
> > In examining the CPU utilization graphs, the CPU generally looks
> > about 5% busy for the first 15 minutes; this would be bmake determining
> > dependency graphs, I expect.
> 
> Is that one process using 100% of one core, or many processes using 5% total?

It's closer to the first, but "which core" varies a bit over time.  (In
one specific instance, core 17, then 13 are at near 100% within that
first 15-minute interval.)

> > Based on earlier work I did, where I was able to do a similar build in a
> > native FreeBSD/i386 (no PAE) enviroment on the same hardware (but when
> > it still only had 6GB RAM), and I managed to get the build done in 2:47,
> > I believe that getting more work done in parallel in this 2:00 period is
> > a key to improving performance: the 2:47 result showed that period to be
> > a very busy one for the CPU.
> 
> You need to know where your bottlenecks are during the build.

Indeed.  :-}

> Since you have lots of RAM, you could try to rule out differences in filesystem access by placing your jail on an mfs and building your software off that.

That's an experiment that I've been advocating, but 96GB isn't enough.

> If that improves build times, then you're IO bound at least some of the time. You should be logging disk access along with CPU and memory during the build.

FWIW, I'm seeing very little CPU time spent in interrupt mode.

I'll see if I can find a reasonable way to munge the output of iostat to
be usable for the purpose, I suppose; thanks.

Peace,
david
-- 
David H. Wolfskill				david at catwhisker.org
Taliban: Evil cowards with guns afraid of truth from a 14-year old girl.

See http://www.catwhisker.org/~david/publickey.gpg for my public key.
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