[svlug] what is Intel hyper-threading?

[Rick Kwan]

Ben Rockwood wrote:

> When in doubt, consult the great and powerful Wikipedia.
> http://en.wikipedia.org/wiki/Hyper-threading

That was pretty good.

> Also, you can get the lowdown on this Intel crock of cra.....ietivity
> from their own lips: http://www.intel.com/technology/hyperthread/
> While I'm not fan of Intel, their manuals aren't terrible so you might
> want to grab a P4 architecture manaul and some strong coffee.

I read that; it was fairly vague for my purposes, which is
what triggered my question.

In digging around, I've discovered that Intel's Hyper-Threading
Technology, Sun's chip multithreading, and other approachs fall
into the domain of "simultaneous multithreading" (SMT).  An
acquaintance directed me to papers written by Dean Tullsen and
Susan Eggers of University of Washington.  They have an intro page
about SMT (http://www.cs.washington.edu/research/smt/).

I've discovered the following about various shipping processors:
   * Intel Xeon - 1 core x 2 threads/core = 2 threads,
     core switches thread on missing resource
   * IBM Power4+ - 2 cores x 1 thread/core = 2 threads
   * IBM Power5 - 2 cores x 2 threads per core = 4 threads,
     core switches thread on missing resource
   * Sun UltraSPARC IV - 2 cores x 1 thread/core = 2 threads
In the above descriptions, missing resource includes:  cache miss,
branch mis-prediction, etc.

Upcoming processors:
   * Sun Niagara - 8 cores x 4 threads/cores = 32 threads,
     core switches thread on CPU cycle (round robin, really!)
   * Intel Itanium 2 Montecito (2 cores) and others (multi-core)
   * AMD Opteron (2 cores) and Athlon64 (2 cores)
I have no information on how many threads the Intel and AMD designs
will support.  Talks on Montecito, Niagara, and Pentium 4 are
scheduled for Hot Chips 16; I hope some SVLUG member is attending.

--Rick Kwan