Re: Does hyper-threading = dual cpu

From: John-Paul Stewart (jpstewart_at_sympatico.ca)
Date: 12/26/03 

Date: Fri, 26 Dec 2003 15:45:43 -0500

Jean-David Beyer wrote:
>
> John-Paul Stewart wrote:
> > chuck wrote:
> >
> >>I just loaded Fedora 1. Didn't pay attention when it booted
> >>up the last time and had a question about a program that was
> >>running so I ran top ... and got:
> >>
> >>CPU states: cpu user nice system irq softirq iowait idle
> >> total 12.4% 69.4% 9.6% 0.0% 0.0% 0.0% 108.0%
> >> cpu00 8.3% 33.7% 4.1% 0.0% 0.0% 0.0% 53.6%
> >> cpu01 4.1% 35.7% 5.5% 0.0% 0.0% 0.0% 54.4%
> >>
> >>or is the system just confused?
> >
> >
> > With hyperthreading enabled and an SMP kernel the OS will see a single
> > hyperthreaded CPU as two CPUs. It won't perform like two physical CPUs
> > but the two logical CPUs will show up seperately in top, xosview,
> > /proc/cpuinfo, and other places.
>
> It may not perform exactly like two CPUs, but the total system
> throughput should be higher than with hyperthreading disabled. It would
> depend on the workload.

Quite true. For example, compiling lots of source files I see a 5%
improvement with hyperthreading. According to benchmarks on an IBM
website they've seen 40% improvement on multi-threaded server tasks.
(I've lost the URL but can probably find it if necessary.) This is
certainly a case of "Your mileage *will* vary".
 
> Now when I get my dual XEON machine running, it will have two
> hyperthreaded CPUs in it. That should be interesting.

You'll love it, I'm sure. My dual hyperthreaded Xeon box is a
screamer. It's kind of fun to see that it thinks there are four CPUs
and reports over 24000 bogomips.

Relevant Pages

  • Re: How useful is Hyper-Threading for average user?
    ... Hyperthreading can ... dual physical CPUs. ... IMHO hyper-threading is non-issue when making a purchasing ...
    (comp.os.linux.hardware)
  • Re: two processors...
    ... It is a Intel Pentium 3.04G ... > No multiple CPUs. ... I don't know about hyperthreading. ... reinstalled the smp kernel and got my 2 CPUs back. ...
    (alt.os.linux.suse)
  • Re: Disable of hyperthreading on Xeon
    ... Brandon Niemczyk mumbled into her beard: ... >> When I boot up the machine, it shows 4 CPUs because of the hyperthreading. ...
    (comp.os.linux.development.system)
  • Re: is xeon hyperthreading considered good or bad?
    ... with hyperthreading on in bios. ... Top now shows me 4 cpus with processes running on all four ... course not to the point of a real dual core. ...
    (comp.unix.bsd.freebsd.misc)
  • Re: Why Two CPUs in Task Mgr?
    ... It is because of the HyperThread feature in the Intel CPU. ... SMT) allows for a single physical processor to appear to the operating ... choice if you wish to use hyperthreading. ... >both of these boxes display two CPUs in Task Manager. ...
    (microsoft.public.win2000.general)
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