Messages in this thread | | | From | (Joe Korty) | Subject | Re: [PATCH] 2.4.18 scheduler bugs | Date | Fri, 15 Mar 2002 17:14:20 -0500 (EST) |
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>>> 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.
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