[gclist] Garbage collection and XML

Emery Berger emery@cs.utexas.edu
Thu, 8 Mar 2001 20:51:10 -0600

> Is that an X86 machine?  I just timed a Pentium III/500/100 machine at
> something near 25 cycles per
> "lock; cmpxchgl".  I'm interested because I've sometimes heard the claim
> that X86 is particularly bad at this, but that hasn't really been
> consistent
> with my experience.  Is this chipset dependent, perhaps?

Timing just the "lock; cmpxchgl" doesn't give you the whole picture. The
problem is that the Pentium flushes the pipeline when it encounters a locked
instruction. The performance penalty is pretty spectacular. I'm told the P4
has a 24-stage pipeline, so locked instructions will become effectively even
more expensive.

-- Emery

Emery Berger