[ntp:questions] Power-saving patch to NTP
David Woolley
david at ex.djwhome.demon.co.uk.invalid
Fri May 16 20:58:43 UTC 2008
Evandro Menezes wrote:
> In terms of performance, yes, but in terms of power, no. If NTP gets
> the CPU out of a deep stand-by state, then it may take hundreds of
> milliseconds for the CPU to go back to that state. Moreover, NTP 1s-
> timer may prevent the CPU from going to even deeper stand-by states.
If it is in a deep stand by state, it is going to take a long time to
service the interrupts from the timing sources, and you are going to get
a large jitter on the time measurements.
The answer to the delay in getting back into standby is for applications
to have an API that can tell the kernel that they are going to sleep,
rather than using timeouts to deduce that.
This smacks of one size fits all. A system that needs accurate time,
most likely won't need to do a lot of intensive power saving. A system
that has extreme power management requirements probably doesn't need
precise time. If it does, it should use special hardware. E.g.
microncontrollers often completely stop the main oscillator, but have a
timer than runs on a completely separate, low power, oscillator.
Another problem you will get with putting the system into deep sleeps is
that the oscillator temperature is going to vary wildly.
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