[time-nuts] DPC Latency

[Bob Camp]

Hi

My concern would be a really bad driver that spikes into the 1,000's of us every so often. Every once in a great while there could be a collision. That would really drive you crazy trying to find it.

Bob
 
On Jun 18, 2011, at 10:04 AM, David J Taylor wrote:

>> Hi
>> 
>> DPC Latency = Deferred Procedure Call Latency = how long it takes Windows to get around to doing what it should do real time. Put another way - how lazy is your computer?
>> It may not be a big issue, but it's probably worth checking for free:
>> http://www.thesycon.de/deu/latency_check.shtml
>> We don't do audio or video since we're serious Time Nuts:)... The same issue would mess up our stuff though. It certainly would be useful to know when playing with NTP.
>> Usual disclaimer - if your PC explodes don't blame me. There are lots of other programs out there that do the same thing. I have no connection with these guys. It's just the first one I found.
>> 
>> Bob
> 
> Bob,
> 
> Yes, that's a program which produces some interesting results, and has been useful for detecting bad behaviour by some poorly written drivers (e.g. when receiving masses of data over a satellite DVB link).
> 
> For NTP, I think you may find that all the time-critical stuff is done at high-priority, and it's only the non-time critical stuff which is done at DPC time.  This is how the DPC is intended to be used, of course.  VMS has a similar mechanism, ASTs, if I recall correctly, but that was a long time ago.
> 
> On Windows with NTP, you can get within a couple of hundred microseconds (XP) or perhaps 50 microseconds (Windows-7) if my graphs here are any guide:
> 
> http://www.satsignal.eu/mrtg/performance_ntp.php
> 
> The best I can offer is within 10 microseconds or so on an Intel Atom system running FreeBSD.  I'm sure that others can do better!
> 
> Cheers,
> David
> -- 
> SatSignal software - quality software written to your requirements
> Web:  http://www.satsignal.eu
> Email:  david-taylor at blueyonder.co.uk 
> 
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.