hyper threading.

[John Pettitt]

Paul A. Hoadley wrote:

>On Sat, Mar 26, 2005 at 11:45:21PM +0100, Anthony Atkielski wrote:
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>>Where can I see the measurements?
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>Here are some measurements.  A few weeks ago I ran Unixbench 4.1.0
>(/usr/ports/benchmarks/unixbench) on a P4 2.8GHz with and without
>hyperthreading enabled.  I note a slight difference in the 10 minute
>load average in favour of the uniprocessor run (0.00 vs 0.10 in the
>hyperthreading run), though I doubt this alone could account for a 15%
>difference in total score.
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>Uniprocessor run:
>-----------------
>  BYTE UNIX Benchmarks (Version 4.1.0)
>  System -- bigbird.logicsquad.net
>  Start Benchmark Run: Sun Feb 20 08:23:08 CST 2005
>   14 interactive users.
>   8:23AM  up 3 days, 14:37, 14 users, load averages: 0.00, 0.00, 0.00
> [snip]
>                                                                 =========
>     FINAL SCORE                                                     270.4
>
>
>Hyperthreading run:
>-------------------
>  BYTE UNIX Benchmarks (Version 4.1.0)
>  System -- bigbird.logicsquad.net
>  Start Benchmark Run: Sun Feb 20 17:22:33 CST 2005
>   2 interactive users.
>   5:22PM  up 2 mins, 2 users, load averages: 0.31, 0.23, 0.10
> [snip]
>                                                                 =========
>     FINAL SCORE                                                     228.9
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Notice the HT run had load on the box (0.31) when it started.  If you're
going to run benchmarks you need to start with a clean reboot before
each run and make sure all the background daemons have been killed and
and  the load is zero.

However even then this is not a good test of HT - the point of HT is to
improve throughput in multi thread workloads and the benchmark suite is
basically single thread.    What would be more interesting would be to
run a test with a constant background load also running.    In theory
the HT should do a better job of balancing the load between the
benchmark and the background than the BSD scheduler can on it's own.   I
don't have an HT box here or I'd try it but I'd love to know how it
comes out if somebody is up for it.


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