hyper threading.

[Anthony Atkielski]

em1897 at aol.com writes:

> I am offerring the correct information. Turning on SMP on
> an HT machine will kill the systems performance much
> more than hyperthreading will gain.

Why?

I've explained why hyperthreading can provide a modest gain in
performance.  Now explain to me why it would not.

> I told him to test.
> The degradation is easily measurable.

If you can say with certainty that a degradation occurs, then you've
already tested, in which case you can show your work.  If you haven't
tested, then you can't say anything with certainty, in which case your
opinions are pure conjecture.

A quick look at actual research done by various parties on the Web
reveals that HT does provide the modest improvements to which I've
alluded.  It's not as impressive as two processors, but then again,
nobody claimed it would be.  It just makes better use of one processor
and allows you to get more for your money from that processor.

One advantage that I had not previous mentioned is that the availability
of a logical processor for dispatch can improve response time in certain
scenarios, even if the overall processor power doesn't increase that
much.  When compute-bound processes monopolize a single processor, the
response time of the entire system can suffer; but if you have a second
processor waiting for dispatch (even a logical HT processor), you can
immediately attend to other tasks even as the compute-bound process
runs, as long as it isn't launching multiple threads (which most such
processes won't do).

-- 
Anthony