PPS undersampling

Gary E. Miller gem at rellim.com
Wed Aug 31 15:50:36 UTC 2016

Yo Hal!

On Wed, 31 Aug 2016 01:19:49 -0700
Hal Murray <hmurray at megapathdsl.net> wrote:

> gem at rellim.com said:
> > Saving power is good, but I suspect the extra power is minimal.  I
> > hace USB power meters, so we can measure this.   
> It depends on the details.  You can save a lot of power by turning
> stuff off. The more you turn off, the more power you save but the
> longer it takes to get running again.  I think most CPUs these days
> have an instruction that is roughly "halt and wait for an
> interrupt".  That lets the CPU turn off the clock for the instruction
> unit so it doesn't have to burn power running a tight loop.  As an
> experiment, you could write some code that goes into a tight loop and
> see if that takes more power than not running anything.

All I care about is how it affects ntpd.  As long as ntpd does a usleep()
the OS will do the right thing.

> The next step is things like putting the memory into self refresh
> mode or turning off the disk controller.

Turning those off is a deep sleep.  That will not work for ntpd.

> USB is ugly to power down since there aren't any interrupt wires.

Yup, not gonna happen.

> In the extreme, you can power off the clock generation circuit.

And then there is no point in running ntpd.

> Your USB power meter should work for a Raspberry Pi or BeagleBone.  I
> assume you have a wall-power meter for a laptop or desktop.

Yeah, but they all average over a good part of a second.  Nothing
ntpd does will move the (virtual) needle.

Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
	gem at rellim.com  Tel:+1 541 382 8588
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