The dynamic tick patch

Posted Jun 9, 2005 16:46 UTC (Thu) by iabervon (subscriber, #722)
In reply to: The dynamic tick patch by dvrabel
Parent article: The dynamic tick patch

IIRC, the power savings doesn't come from the CPU being in sleep for more total time; it comes from switching into and out of sleep less often. There is some delay after the instruction to go to sleep before the power usage actually drops substantially, and, on an idle system, this is significant. It's a smaller effect, but generally similar to the reason that laptops want disk access bunched up instead of evenly spread.

Also, for a system where the virtual processor being idle means more time for other virtual processors, going from 99.5% idle to 99.9% idle means that the cost of an extra idle system is cut by a factor of 5.