[ntp:questions] Power-saving patch to NTP

David L. Mills mills at udel.edu
Mon May 19 17:53:58 UTC 2008


Evandro,

I don't know wwhat CPU you have, but mine doesn't boil 100 W all the 
time. You realize that is 30 A at 3.3 V. As I have said several times, 
if you expect ntpd to discipline the frequency, the CPU needs to nudge 
the time on a regular basis, like once per second. It could be less 
often with the penalty being increased sawtooth error. If this is 
objectional, for goodness sake don't use ntpd.

I feel very stongly that the present discussion is a colossal red 
herring and has nothing whatsoever to do with the present ntpd design. 
The present design is optimized as a compromise between a casual 
workstation and a busy server with 3000 packets per second. Make a new 
product specification and discontinue any mention of ntpd.

Dave

Evandro Menezes wrote:
> On May 16, 6:44 pm, "David L. Mills" <mi... at udel.edu> wrote:
> 
>>With respect, you miss the point. The ntpd does not require a tickle
>>every second just to scan for polls; it requires that tickle in order to
>>discipline the clcok frequency. The additional cycles necessary to link
>>to the next association structure, then increment and test a variable,
>>are way, way down in the noise.
> 
> 
> I don't pretend to know NTP innards, but wouldn't it be possible to
> select the scale of updates?
> 
> And, please, don't consider the power used by NTP itself, but rather
> the power used by the CPU idling in a higher power state than before
> NTP woke it up.  Modern processors can draw 100W without doing
> anything useful, but it falls down to less than 10W it it's allowed
> run the HALT instruction instead when there's nothing to do.
> 
> The picture that Red Hat refers to is that the CPU is removed from a
> deep C-state in order to run NTP for microseconds and then it remains
> in the running state for a few fractions of a second until it goes
> back to a deep C-state.  So it's not a matter of NTP's duty cycle, but
> the duty cycle resulting from the heuristics used by the hardware or
> the OS to decide when to place the CPU in a deep C-state.
> 
> HTH




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