Re: [announce] [patch] ultra-scalable O(1) SMP and UP scheduler

Linus Torvalds
2002-01-07T03:18:02Z

On Sun, 6 Jan 2002, Richard Henderson wrote:
> On Sun, Jan 06, 2002 at 02:13:32AM +0000, Alan Cox wrote:
> > ... since an 8bit ffz can be done by lookup table
> > and that is fast on all processors
>
> Please still provide the arch hook -- single cycle ffs type
> instructions are still faster than any memory access.

This is probably true even on x86, except in benchmarks (the x86 ffs
instruction definitely doesn't historically count as "fast", and a table
lookup will probably win in a benchmark where the table is hot in the
cache, but you don't have to miss very often to be ok with a few CPU
cycles..)

(bsfl used to be very slow. That's not as true any more)

Linus