[svlug] what is Intel hyper-threading?

Joe Buck Joe.Buck at synopsys.COM
Wed Jul 28 14:52:52 PDT 2004


On Wed, Jul 28, 2004 at 07:38:08AM -0700, Rick Kwan wrote:
> I can't figure Intel's "Hyper-Threading Technology"; it
> doesn't seem to be multiple cores.  Nobody claims it is
> emulating multiple CPUs like Niagara.  What the heck is it??

Because processor speed is increasing much faster than DRAM speed,
these days a cache miss can cost more than a hundred CPU cycles.
It's starting to look like a page fault, so the idea of hyperthreading
is to treat it like one: switch to another process while waiting for
the fault to be satisfied..

A hyperthreaded processor has multiple register contexts (in the simplest
case, two sets of registers).  If the current process gets stuck (say,
because of a cache miss), the processor can switch to the other process,
using the other register set.  In addition, because there are multiple
functional units, in some cases both process contexts can be active at the
same time.




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