numbers don't lie ...

[Mike Meyer]

In <E1GNOLq-000DC2-1Q at cs1.cs.huji.ac.il>, Danny Braniss <danny at cs.huji.ac.il> typed:
> Im testing these 2 boxes, Sun X4100 and Dell-2950, and:
> 
> 	SUN X4100:	Dual Core AMD Opteron(tm) Processor 280 (2393.19-MHz K8-class CPU)
> 			one 70g sata disk
> 	DELL 2950:	Intel(R) Xeon(TM) CPU 3.20GHz (3192.98-MHz K8-class CPU)
> 			4 sata disks + raid0
> 
> they both run identical 6.1-STABLE.
> 
> my 'cpu benchmark' shows the amd being much better than the intel.
> but, doing a make buildworld give interesting results:
> 
> dell-2950 : make -j16 TARGET_ARCH=amd64 buildworld : 24m17.41s real 1h3m3.26s 
> user 17m15.07s sys
> dell-2950 : make -j8 TARGET_ARCH=amd64 buildworld : 24m8.28s real 1h2m59.38s 
> user 16m16.20s sys
> 
> sunfire : make -j16 TARGET_ARCH=amd64 buildworld : 24m21.38s real 49m6.68s 
> user 14m22.64s sys
> sunfire : make -j8 TARGET_ARCH=amd64 buildworld : 23m47.69s real 48m53.58s 
> user 13m44.81s sys
> 
> which probably says something about my 'cpu benchmark' :-(

Yes - that it's not very good at predicting performance on a parallel
make. That's not surprising, as it's true of most benchmarks. You
might want to check out some of the benchmarks in the ports tree as
well.

> but why is the user time so much different between the boxes?

What's the CPU configuration? The AMD is dual core - is that it? Could
the Xeon be dual-core and hyperthreaded, so it's got that many more
CPUs to contribute towards user time?

To illustrate, I have numbers for "make -j4" for a P4 with and without
hyperthreading enabled:

machdep.hyperthreading_allowed: 1 -> 0
     50m55.99s real      35m28s.19 user       8m20s.02 sys
machdep.hyperthreading_allowed: 0 -> 1
     38m48s.85 real      55m2s.43 user       12m27s.90 sys

Note the effect of the second CPU on the user time.

	<mike
-- 
Mike Meyer <mwm at mired.org>		http://www.mired.org/consulting.html
Independent Network/Unix/Perforce consultant, email for more information.