On Mon, 18 Feb 2002, Matthew Dillon wrote:
> :
> :I can't see any major problem with this but I can't help thinking that
> :there must be one.. on UP the question is: "who is going to
> :release the lock if no-one is runnable?"
>
> An interrupt, of course. Wakeups don't happen out of thin air! This
> is true of 1.x, 2.x, 3.x, 4.x, 5.x, UP, and SMP. Something needs to
> trigger the event that causes the wakeup to occur.
>
> :can you detail in more clarity the flip-flopping you were seeing?
>
> Basically what is happening is that switch/wakeup overhead is being
> imposed unnecessarily. There is no need to switch if there is nothing
> to switch to, and this also causes the other process to not have to
> wakeup anyone when it releases Giant because process #1 is spinning
> on it instead of sleeping on it. So you immediate remove four context
> switches from the critical path.
true, though the original code would halt the processor to reduce power
consumption on laptops etc. procrunnable doesn't include the idle
process. (a side-effect).
>
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