On Wed, Jan 19, 2005 at 05:15:34PM +0000, Peter O'Kane wrote:
> Good point. Further results here running make -j8 to build a 2.0 kernel:
> 
> Real	User	System	Configuration
> 288.12	255.15	35.97		Single processor no HT
> 251.72	440.61	49.55		Single processor with HT
> 165.58	260.00	40.74		Twin physical processors no HT
> 151.54	435.04	69.11		Twin physical processors with HT
> 
> again running make -j16
> 
> 160.9	263.44	44.24		Twin physical processors no HT
> 146.46	452.66	78.69		Twin physical processors with HT
> 
> and finally make -j32
> 
> 158.82	260.33	42.63		Twin physical processors no HT
> 146.23	465.37	77.8		Twin physical processors with HT
> 
> Note that the user/system time required to do the job remains fairly 
> constant at about 250-260/30-45 seconds with HT off. With HT enabled the 
> user/system time required rises to about 440-460/50-70 seconds.
> It appears that HT gives about 10% overall performance boot for many tasks 
> but the effective processor speed seen by a single thread is 55%-60% of the 
> speed of the processor in non HT mode.

This matches what I've noticed when I tested a single-CPU P4 system (although
I though the gain was more like 6-7% than 10%).

-- 
Manuel Bouyer <bouyer@antioche.eu.org>
     NetBSD: 26 ans d'experience feront toujours la difference
--