Some mmap observations compared to Linux 2.6/OpenBSD

[Ted Unangst]

On Sat, 25 Oct 2003, Terry Lambert wrote:

> Why does the benchmark need to be "fixed" for OpenBSD and not
> for any other platform?

openbsd does not have a unified cache between file system (pread) and vm
(mmap) interfaces.  in the real world, it's unusual to find an application
that uses both interfaces for its data files.  a good benchmark at least
attempts to model real world application behavior.

> My point here is that a benchmark measures what it measures, and
> if you don't like what it measures, making it measure something
> else is not a fix for the problem that it was originally intended
> to show.

then the benchmark author should explain what's going on.  "touching a
cached page" and "touching a page and reading it from disk" are different
events.  if the name of the graph were "reading an mmaped page after
priming the disk cache with pread", then fine.  but it's not.

i'd like a benchmark to either attempt to accurately model (some slice
of) real life or accurately explain what it is measuring.


-- 
"I am clearly more popular than Reagan.  I am in my third term.
Where's Reagan?  Gone after two!  Defeated by George Bush and
Michael Dukakis no less."
      - M. Barry, Mayor of Washington, DC