The dynamic tick patch

Posted Jun 9, 2005 11:05 UTC (Thu) by dvrabel (subscriber, #9500)
Parent article: The dynamic tick patch

I can't seem to find any benchmarks or testing of real-world power-savings from this patch.

The patch is, presumably, putting the processor into a deeper sleep mode since the power savings from just reducing the timer tick frequency is minimal (if the CPU is 99.5% idle then making it 99.9% idle isn't a big different).

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The dynamic tick patch

Posted Jun 9, 2005 16:46 UTC (Thu) by iabervon (subscriber, #722) [Link]

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.