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Subject: Re: HT: good or bad feature??

Author: Slater Wold

Date: 19:27:46 05/27/04

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On May 27, 2004 at 20:16:25, Bernardo Wesler wrote:

>I wonder why some people say that HT is useless, and some other say it is good?
>But the main point at least for me, is to know what is HT really? Which are the
>pros and no-pros? Further details, welcome!!
>Thx in advance
>Dr Wesler

I had a P4 (with HTing) and it was a neat feature for "free".  It's tricky
though.  It can help, and it can hinder.

It can help in that 2 programs (different programs, and not chess programs) will
run better than on a 'standard' CPU.  When I say better, I mean if they are both
using CPU time, they both will run faster than a 'standard' CPU.

It can hinder a chess program, because a lot of people seem to think you can run
ponder=on matches; you cannot.  Also, most SMP programs will get a 20%ish
speedup, but Crafty is now NUMA, and it can actually deteriate performace.  So
then you'd want to set CPUS=1.  Well, then you're going to split it between the
physical and logical CPU, and it's going to run like crap.  So then you have to
set your affnity to a single CPU, and remember to do that everytime.

Told you it's tricky.



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