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Re: To hyper-thread or not to hyper-thread



On Mon, 2009-12-07 at 09:44 -0700, Greg Woods wrote: 
> On Mon, 2009-12-07 at 16:18 +0100, Joerg Bergmann wrote:
> 
> > 
> > The problem of the Pentium 4 D: It is not really a dual core one.
> > Hyper-Threading means: There is one core with two execution paths, which
> > means some of the common CPU features, but not all, are present twice.
> 
> One feature in particular that is not present twice is some of the
> caching. This is sort of why they named it "hyperthreading". If you can
> get multiple threads of the same process, sharing the same memory, to
> run simultaneously, there is a performance boost. But if you try to run
> two completely different processes simultaneously, there will actually
> be a performance LOSS because of all the cache misses this will cause.
> 
> --Greg
> 
> 
As far as I can tell both cores have their separate 1M cache. But
lshw-gui reports HT is supported but looking at the files in /sys makes
me doubt it. For example:
/sys/devices/system/node/node0/cpu1/online
does not exist. But that may be because the BIOS has turned HT off.
--
=======================================================================
A complex system that works is invariably found to have evolved from a
simple system that works.
=======================================================================
Aaron Konstam telephone: (210) 656-0355 e-mail: akonstam sbcglobal net


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