HT Benchmarks (was: /proc/cpuinfo and hyperthreading)

[Scott Robert Ladd]

Måns Rullgård wrote:
> It's easy to write a program that displays any number of graphs
> vaguely related to the system load.  How do we know that the
> performance meter isn't lying?

We don't.

All I can say is that the performance meter seems (note the weasel-word)
proper when running Win2K SMP on a dual PIII-933 box at one of my client
sites. However, such experience does *not* guarantee that WinXP is reporting
valid numbers for a P4 with HT.

Here's a little test I ran this morning, now that my new system is
operational. My benchmark is a full "make bootstrap" compile of gcc-3.2.1,
with and without the - j 2 make switch that enables two threads of
compilation. Using the 2.5.51 SMP kernel, I see the following compile times:

  SMP     w/o  -j 2: 28m11s
  "nosmp" with -j 2: 27m32s
  SMP     with -j 2: 24m21s

HT appears to give a very tiny benefit even without an SMP kernel -- and
*with* an SMP kernel, I get a 16% improvement in my compile time. That
pretty much matches my expectation (i.e., a HT processor is *not* equal to
dual processor, but it *is* better than a non-HT processor).

Just some food for collective thought.

..Scott