Hotsos Symposium Speaker – Neil Gunther

Neil Gunther is a returning Hotsos Symposium presenter.


Neil GuntherNeil J. Gunther, M.Sc., Ph.D., is an internationally known performance researcher and consultant who founded Performance Dynamics Company in 1994. He is the author of 3 books and many technical papers and presentations on performance analysis and capacity planning. Dr. Gunther received the prestigious A.A. Michelson Award from CMG in 2008, and was elected a senior member of both ACM and IEEE in 2009.

Presentation Title

Superlinear Scalability: The Perpetual Motion of Parallel Performance


Many Hotsos attendees know that the Universal Scalability Law (USL) quantifies performance measurements and predictions. The USL contention and coherency parameters quantify the usual SUBLINEARITY. More recently, the USL has been criticized for failing to model SUPERLINEAR scalability, viz., where you get more performance than the available capacity would be expected to support.

Like a perpetual-motion contraption that violates the law of conservation of energy, one would like to simply dismiss such claims. Although some superlinear data are clearly spurious, other data belong to repeatable measurements that are not easily explained away: the implication being that a third parameter would fit those data. But this poses several serious problems:

  • People (wrongly) tend to believe data, not models.
  • More parameters generally weaken modeling conclusions.
  • Superlinearity is more likely to occur in cluster databases.
  • Not accommodating superlinearity could dissuade people from using the USL.

Surprisingly, Dr. Gunther found that the USL can accommodate superlinear data WITHOUT the introduction of another parameter. But something else changes that also warns about modeling unphysical effects: like a perpetual-motion detector. Moreover, there is a "pay the piper" penalty for superlinear performance.

Dr. Gunther will demonstrate this remarkable result with examples.

Presentation Materials

Presentation materials are available online to attendees only.


The speaker schedule is as follows: