Mailinglist Archive: opensuse (3217 mails)
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Re: [SLE] What are the stats on hyperthreading? I may need a Mobo.
- From: Bruce Marshall <bmarsh@xxxxxxxxxx>
- Date: Fri, 5 Mar 2004 08:13:57 -0500
- Message-id: <200403050813.57573.bmarsh@xxxxxxxxxx>
On Friday 05 March 2004 08:01 am, Anders Johansson wrote:
> On Friday 05 March 2004 13.57, Bruce Marshall wrote:
> > On Friday 05 March 2004 07:27 am, Bruce Marshall wrote:
> > > On Friday 05 March 2004 02:02 am, Steven T. Hatton wrote:
> > > > I would more than likely go with a 64bit chip before I went to two
> > > > processors. The inter-processor protocols, the physical parameters
> > > > introduced by the finite propagation speed of electromagnetic
> > > > impulses, and the need for software to support (external) SMP make it
> > > > unattractive.
> > >
> > > I have a P4 2.8 running quite nicely here with HT. Can we gin up some
> > > simple test to see what it does?
> >
> > I think I have an answer for you and Lee is right.
> >
> > I wrote a simple looping program that would show the elapsed time for
> > nnnn passes through the loop. Run by itself, a valid time would be 1.55
> > secs for one pass. Start up another copy of the same program, and the
> > time for each became 2.9. Close enough to twice the time that it's
> > obvious the HT is a sham.
>
> I think you miss the point of HT. HT lets the CPU do other things while it
> would otherwise be idle, such as for external IO and data fetching. It's an
> idea to avoid pipeline stalls. In real world settings, most benchmarks show
> something like a 30% improvement in performance.
>
> What exactly does your loop do, other than just loop that is?
No, I didn't miss that point..... It's true that in some instances two cpu's
(even of 1/2 the power of one) can be a better deal, but not very often.
However, comparing a 2.8 P4 without HT to a dual-cpu 1.4 setup (a fair
comparison), there is one advantage: when there's only one task to perform,
it gets a cpu of 2.8ghz instead of just 1.4ghz.
For the money, the HT doesn't really have any disadvantages that I can see, it
just doesn't have all the advantages of two P4 2.8's. (which would cost a
lot more money)
--
+----------------------------------------------------------------------------+
+ Bruce S. Marshall bmarsh@xxxxxxxxxx Bellaire, MI 03/05/04 08:08 +
+----------------------------------------------------------------------------+
"The Information Highway: 500 channels and not a thing to watch."
> On Friday 05 March 2004 13.57, Bruce Marshall wrote:
> > On Friday 05 March 2004 07:27 am, Bruce Marshall wrote:
> > > On Friday 05 March 2004 02:02 am, Steven T. Hatton wrote:
> > > > I would more than likely go with a 64bit chip before I went to two
> > > > processors. The inter-processor protocols, the physical parameters
> > > > introduced by the finite propagation speed of electromagnetic
> > > > impulses, and the need for software to support (external) SMP make it
> > > > unattractive.
> > >
> > > I have a P4 2.8 running quite nicely here with HT. Can we gin up some
> > > simple test to see what it does?
> >
> > I think I have an answer for you and Lee is right.
> >
> > I wrote a simple looping program that would show the elapsed time for
> > nnnn passes through the loop. Run by itself, a valid time would be 1.55
> > secs for one pass. Start up another copy of the same program, and the
> > time for each became 2.9. Close enough to twice the time that it's
> > obvious the HT is a sham.
>
> I think you miss the point of HT. HT lets the CPU do other things while it
> would otherwise be idle, such as for external IO and data fetching. It's an
> idea to avoid pipeline stalls. In real world settings, most benchmarks show
> something like a 30% improvement in performance.
>
> What exactly does your loop do, other than just loop that is?
No, I didn't miss that point..... It's true that in some instances two cpu's
(even of 1/2 the power of one) can be a better deal, but not very often.
However, comparing a 2.8 P4 without HT to a dual-cpu 1.4 setup (a fair
comparison), there is one advantage: when there's only one task to perform,
it gets a cpu of 2.8ghz instead of just 1.4ghz.
For the money, the HT doesn't really have any disadvantages that I can see, it
just doesn't have all the advantages of two P4 2.8's. (which would cost a
lot more money)
--
+----------------------------------------------------------------------------+
+ Bruce S. Marshall bmarsh@xxxxxxxxxx Bellaire, MI 03/05/04 08:08 +
+----------------------------------------------------------------------------+
"The Information Highway: 500 channels and not a thing to watch."
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