[Top][All Lists]
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [gpsd-dev] PPS over USB
From: |
Hal Murray |
Subject: |
Re: [gpsd-dev] PPS over USB |
Date: |
Mon, 07 May 2012 23:54:36 -0700 |
address@hidden said:
> But we're not sure we can trust NTP. That's the whole problem; if
> bufferbloat really is inducing very large, very short-period latency spikes,
> it may be screwing with the symmetry and statistical-smoothness assumptions
> that NTP synchronization relies on.
It's pretty obvious that ntpd gets confused if you have a long period of
asymmetric routing. I (and probably you) can easily generate that by
downloading a CD or youtube show. Probably the worst case is browsing the
web with a browser that tries to be helpful by loading lots of pictures in
parallel and/or preloading stuff that you might click, or doing that while
you have a download going.
My DSL connection sees occasional queuing delays of over 3.5 seconds.
It might be possible to avoid most of the problems with a big enough huffpuff
parameter and/or appropriate tweaks to other parameters. I haven't studied
this area carefully.
> One of the explicit goals of the Cosmic Backround Bufferbloat Detector is to
> sanity-check NTP.
If you see anything that seems unreasonable, please let me know. ntpd has a
huge collection of heuristics (hacks?) that try to filter out all sorts of
quirks/glitches. I'm sure there are some cases that will get past the
current filters.
--
These are my opinions. I hate spam.
- Re: [gpsd-dev] PPS over USB, (continued)
- Re: [gpsd-dev] PPS over USB, Ed W, 2012/05/07
- Re: [gpsd-dev] PPS over USB, Terje Mathisen, 2012/05/07
- Re: [gpsd-dev] PPS over USB, Ed W, 2012/05/07
- Re: [gpsd-dev] PPS over USB, Gary E. Miller, 2012/05/07
- Re: [gpsd-dev] PPS over USB, Hal Murray, 2012/05/07
- Re: [gpsd-dev] PPS over USB, Eric S. Raymond, 2012/05/07
- Re: [gpsd-dev] PPS over USB, Dave Taht, 2012/05/07
- Re: [gpsd-dev] PPS over USB, Eric S. Raymond, 2012/05/07
- Re: [gpsd-dev] PPS over USB,
Hal Murray <=
- Re: [gpsd-dev] PPS over USB, Eric S. Raymond, 2012/05/08
- Re: [gpsd-dev] PPS over USB, Ed W, 2012/05/08
- Re: [gpsd-dev] PPS over USB, Dave Taht, 2012/05/08
- Re: [gpsd-dev] PPS over USB, Eric S. Raymond, 2012/05/08
- Re: [gpsd-dev] PPS over USB, Ed W, 2012/05/08
- Re: [gpsd-dev] PPS over USB, tz, 2012/05/08
- Re: [gpsd-dev] PPS over USB, Eric S. Raymond, 2012/05/08
- Re: [gpsd-dev] PPS over USB, Ed W, 2012/05/08
- Re: [gpsd-dev] PPS over USB, Eric S. Raymond, 2012/05/08
Re: [gpsd-dev] PPS over USB, Gary E. Miller, 2012/05/03