Re: [PATCH] 2.4.18 scheduler bugs

[Joe Korty]

>>> but even in the Athlon case an IPI is still an IRQ entry, which will add
>>> at least 200 cycles or more to the idle wakeup latency.
>> 
>> It is an idle cpu that is spending those 200 cycles.
> 
> wrong. When it's woken up it's *not* an idle CPU anymore, and it's the
> freshly woken up task that is going to execute 200 cycles later...

I have to disagree.  It is the woken up task *running on the
otherwise idle CPU* that burns up 200 cycles at the tail.

A cpu is wasting, say, 5,000,000 cycles (1GHz/100/2, or 1/2 tick) in
hlt when it could have been doing work.  Why worry about an
alternative wakeup path that burns up 200-400 cycles of that on the
otherwise idling cpu, even if it is at the tail.

Joe