So the GPS is an STA8090 automotive-grade, makes sense as Dishy gets proper hot! Also supports sensor fusion for eg pointing in the right azimuth. https://www.st.com/en/automotive-infotainment-and-telematics/gnss-ics.html However, the beauty of GPS sync is we can choose our own time base external to Dishy :-) Best, Mike On Jun 12, 2021, 01:00 +0200, Dave Taht , wrote: > > > > On Jun 11, 2021, at 3:39 PM, Dave Taht wrote: > > > > > > > > > On Jun 11, 2021, at 3:34 PM, Mike Puchol wrote: > > > > > > We know that Starlink recalculates topology every 15 seconds (this guy, who obviously has way too much spare time, came up with an indirect observation of this interval: https://blog.beerriot.com/2021/02/14/starlink-raster-scan/ ) > > > > > > If we could align with this, we could at least know when potential changes in path delays happen, and try to observe other changes that happen at a similar cadence. > > > > > > Other thoughts, try to plug more details out of the gRPC data, setup GPS-synced probes with a device at the exit PoP, measure differences between time-sync probes to an array of endpoints. > > > > > > > It’s ironic that the device has to have gps in it, and thus should be  able to provide perfect time to clients directly behind it, isn’t. > > > > I haven’t captured a dhcp or dhcpv6 transaction yet myself, > > do they have a ntp option? > > > > What gps software or driver might they have used? (esr’s gpsd is quite popular, but there are others) > > > > What’s the gps chip? > > > > It would be good to have solid time everywhere, as I am seeing clocks not synced even close to 40ms accuracy of late. > > BTW, Eric Raymond (esr) is also one of the driving forces behind ntpsec, along with gary and a few other people now on our list. > > For more details, see: > https://www.ntpsec.org/ > > Once upon a time, I sat in esr's basement hearing him rip much crud out of the old ntpd codebase over the course of a very few days. The shouts “What? WHAAAT?” and most of the other pithy comments he made never made the git log. > > Over the years following the codebase got better and better, but adoption has been slow. > > An intro to that woefully underfunded project: > > NTPsec project - a secure, hardened, and improved implementation of Network Time Protocol derived from NTP Classic, Dave Mills’s original. > NTPsec, as its name implies, is a more secure NTP. Our goal is to deliver code that can be used with confidence in deployments with the most stringent security, availability, and assurance requirements. > Towards that end we apply best practices and state-of-the art technology in code auditing, verification, and testing. We begin with the most important best practice: true open-source code review. The NTPsec code is available in a public git repository. One of our goals is to support broader community participation. > > > > > > Has nobody attacked the JTAG connector on a Dishy yet? > > I reached out to one of the teardown folk (mike (mikeonsoftware?)) months ago to get the debris but the rightest answer was to drill down into it on a still-alive ones. > > > > > > > Best, > > > > > > Mike > > > On Jun 12, 2021, 00:14 +0200, David Collier-Brown , wrote: > > > > OK, Oh Smarter Colleagues, the challenge to you is to say if there is a "natural" place to capture state changes to get the data we want, and if so, is it common or similar enough between drivers to be worthy of attention? > > > > --dave > > > > On 2021-06-09 9:15 a.m., Dave Taht wrote: > > > > > > > > > > > > > > > > Begin forwarded message: > > > > > > > > > > > > From: David Collier-Brown > > > > > > Subject: Microstate Accounting and the Nyquist problem > > > > > > Date: June 9, 2021 at 4:44:14 AM PDT > > > > > > To: Dave Taht > > > > > > Cc: Dave Collier-Brown > > > > > > Reply-To: davecb@spamcop.net > > > > > > > > > > > > A million years ago (roughly around Solaris 9), Sun was suffering from the same problems in measuring their dispatcher as you are with "sloshing". > > > > > > A CPU would be 100% busy in one microsecond, 10% busy in the next gazillion, and the average CPU utilization for our sample period would be maybe 10.1, if the sampler happened to sample right when the spike was happening. > > > > > > This was utterly useless for things like the fair-share scheduler, so it got fixed in Solaris 10, by having the dispatcher record the time a process (well, kernel thread) had spent in a state when the state changed. > > > > > > Initially "microstate accounting" could be toggled on and off, but the branch-around cost more time than always doing the calculation (as discovered by my mad friend Fred) and the kernel folks left it on. It's on to this day. > > > > > > In Simon Sundberg's talk, the opportunity to measure occurs every 1,000 packets, when a suitable timestamp is provided. While the eBPF program can look at every packet and do after-the-fact book-keeping in a map, that's only good if the phenomenon you're measuring is persistent enough that it's around for ~2,000 packets. > > > > > > I'm going to suggest that the right place to record the information you want is right where the event happens.  Preferably in c code, as performance is easy to mess up, but perhaps with an eBPF mechanism to export it. > > > > > > In previous Solaris work, I reliably found that exporting kstats was a darn sight harder than collecting them, and in Eric's blog post[1] he notes that converting time is expensive and best done long after collecting, when someone wanted to read the data. > > > > > > There was an effort to do kstats in Linux[2], but it had supposedly poor performance, and actual trouble when the clock frequency changed. > > > > > > Is there, in your opinion, a "natural" place to capture state changes to get the data you want, and if so, is it common or similar enough between drivers to be worthy of attention? > > > > > > --dave > > > > > > > > > > > > References: > > > > > > > > > > > > 1. Solaris: http://dtrace.org/blogs/eschrock/2004/10/13/microstate-accounting-in-solaris-10/ > > > > > > 2. A failing Linux effort: https://lwn.net/Articles/127296/, https://sourceforge.net/projects/microstate/ > > > > > > > > > > > > -- > > > > > > David Collier-Brown, | Always do right. This will gratify > > > > > > System Programmer and Author | some people and astonish the rest > > > > > > davecb@spamcop.net | -- Mark Twain > > > > > > > > > _______________________________________________ > > > > Starlink mailing list > > > > Starlink@lists.bufferbloat.net > > > > https://lists.bufferbloat.net/listinfo/starlink > > > _______________________________________________ > > > Starlink mailing list > > > Starlink@lists.bufferbloat.net > > > https://lists.bufferbloat.net/listinfo/starlink > > > > _______________________________________________ > > Starlink mailing list > > Starlink@lists.bufferbloat.net > > https://lists.bufferbloat.net/listinfo/starlink >