>I was under the impression that a locked instruction was essentially free
>at runtime, with the sole exception of being one byte larger.
No, they are very expensive, at least when done in a minimal loop (8
cycles on my P5/133 UP and 16 cycles on my Celeron/450). ISTR Steve
Passe saying that they took 30 cycles on an early SMP system.
>Also, with the posted example, atomic_cmpex() is #ifndef I386_CPU - that
>means it won't be available on any of the default kernels, either at
>install time or for 99% of post-install systems built from a release.
No one seems to have noticed dropping of support for coprocessorless/
working-FPU-emulatorless systems in cc (the default for -ffancy-math-387
changed from off to on with egcs).
Bruce
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