> At least on AIX it looks like the select with 0 timeout is a noop, and does not
> yield the processor. There was discussion, that other OS's (BSD) also does an
> immediate return in case of 0 timeout.
>
> Minimum select(2) delay is 1 msec on AIX (tested with Tom's test.c).
>
> So, what was the case against using yield (2) ?
BSDi doesn't have yield(). It does have sched_yield(), but that
controls threads:
force the current pthread to be rescheduled
so there doesn't seem to be any portable way to do this. Sleeps of zero
do no kernel call, and sleeps > 0 sleep for a minimum of one tick.
If you really want a near-zero sleep, you need to do a no-op kernel
call, like umask(), but doing a simple kernel call usually is not enough
because kernels usually favor the last-running process because of the
CPU cache. We need a "try to schedule someone else if they are ready to
run, if not, return right away" call.
I think ultimately, we need the type of near-committers feedback, but
not for 7.1.
-- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610)
853-3000+ If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill,
Pennsylvania19026
