<div dir="auto">Ha, that’s a great point about the GPS/NTP thing. </div><div dir="auto"><br></div><div dir="auto">GPS chip, not sure, there’s only one tear down I’ve seen, here’s the gps chip: <div dir="auto"><a href="https://cdn.arstechnica.net/wp-content/uploads/2020/12/starlink-28-gps-receiver.jpg">https://cdn.arstechnica.net/wp-content/uploads/2020/12/starlink-28-gps-receiver.jpg</a> </div><div dir="auto"><br></div><div dir="auto">No idea about the software, maybe I’ll try to JTAG mine. </div></div><div dir="auto"><div><br></div></div><div dir="auto"><br></div><div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Fri, Jun 11, 2021 at 3:39 PM Dave Taht <<a href="mailto:davet@teklibre.net">davet@teklibre.net</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;padding-left:1ex;border-left-color:rgb(204,204,204)"><div style="word-wrap:break-word;line-break:after-white-space"><br><div><br><blockquote type="cite"><div>On Jun 11, 2021, at 3:34 PM, Mike Puchol <<a href="mailto:mike@starlink.sx" target="_blank">mike@starlink.sx</a>> wrote:</div><br><div>
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<div dir="auto">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: <a href="https://blog.beerriot.com/2021/02/14/starlink-raster-scan/" target="_blank">https://blog.beerriot.com/2021/02/14/starlink-raster-scan/</a> )<br>
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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.<br>
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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.<br>
<br></div></div></div></div></blockquote><div><br></div>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.</div><div><br></div><div>I haven’t captured a dhcp or dhcpv6 transaction yet myself,</div><div>do they have a ntp option?</div><div><br></div><div>What gps software or driver might they have used? (esr’s gpsd is quite popular, but there are others) </div><div><br></div><div>What’s the gps chip?</div></div><div style="word-wrap:break-word;line-break:after-white-space"><div><br></div><div><br><blockquote type="cite"><div><div><div name="messageBodySection"><div dir="auto">
Has nobody attacked the JTAG connector on a Dishy yet?</div>
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Best,<br>
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Mike</div>
<div name="messageReplySection">On Jun 12, 2021, 00:14 +0200, David Collier-Brown <<a href="mailto:davecb.42@gmail.com" target="_blank">davecb.42@gmail.com</a>>, wrote:<br>
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<div><p>OK, <i>Oh Smarter Colleagues</i>, 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?<br></p><p>--dave<br></p>
<div>On 2021-06-09 9:15 a.m., Dave Taht wrote:<br></div>
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<div>Begin forwarded message:</div>
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<div style="margin:0px"><span style="font-family:-webkit-system-font,"Helvetica Neue",Helvetica,sans-serif"><b style="font-family:-webkit-system-font,"Helvetica Neue",Helvetica,sans-serif">From:</b></span> <span style="font-family:-webkit-system-font,"Helvetica Neue",Helvetica,sans-serif">David Collier-Brown <<a href="mailto:davecb.42@gmail.com" target="_blank" style="font-family:-webkit-system-font,"Helvetica Neue",Helvetica,sans-serif">davecb.42@gmail.com</a>><br></span></div>
<div style="margin:0px"><span style="font-family:-webkit-system-font,"Helvetica Neue",Helvetica,sans-serif"><b style="font-family:-webkit-system-font,"Helvetica Neue",Helvetica,sans-serif">Subject:</b></span> <span style="font-family:-webkit-system-font,"Helvetica Neue",Helvetica,sans-serif"><b style="font-family:-webkit-system-font,"Helvetica Neue",Helvetica,sans-serif">Microstate Accounting and the Nyquist problem</b><br></span></div>
<div style="margin:0px"><span style="font-family:-webkit-system-font,"Helvetica Neue",Helvetica,sans-serif"><b style="font-family:-webkit-system-font,"Helvetica Neue",Helvetica,sans-serif">Date:</b></span> <span style="font-family:-webkit-system-font,"Helvetica Neue",Helvetica,sans-serif">June 9, 2021 at 4:44:14 AM PDT<br></span></div>
<div style="margin:0px"><span style="font-family:-webkit-system-font,"Helvetica Neue",Helvetica,sans-serif"><b style="font-family:-webkit-system-font,"Helvetica Neue",Helvetica,sans-serif">To:</b></span> <span style="font-family:-webkit-system-font,"Helvetica Neue",Helvetica,sans-serif">Dave Taht <<a href="mailto:davet@teklibre.net" target="_blank" style="font-family:-webkit-system-font,"Helvetica Neue",Helvetica,sans-serif">davet@teklibre.net</a>><br></span></div>
<div style="margin:0px"><span style="font-family:-webkit-system-font,"Helvetica Neue",Helvetica,sans-serif"><b style="font-family:-webkit-system-font,"Helvetica Neue",Helvetica,sans-serif">Cc:</b></span> <span style="font-family:-webkit-system-font,"Helvetica Neue",Helvetica,sans-serif">Dave Collier-Brown <<a href="mailto:dave.collier-brown@indexexchange.com" target="_blank" style="font-family:-webkit-system-font,"Helvetica Neue",Helvetica,sans-serif">dave.collier-brown@indexexchange.com</a>><br></span></div>
<div style="margin:0px"><span style="font-family:-webkit-system-font,"Helvetica Neue",Helvetica,sans-serif"><b style="font-family:-webkit-system-font,"Helvetica Neue",Helvetica,sans-serif">Reply-To:</b></span> <span style="font-family:-webkit-system-font,"Helvetica Neue",Helvetica,sans-serif"><a href="mailto:davecb@spamcop.net" target="_blank" style="font-family:-webkit-system-font,"Helvetica Neue",Helvetica,sans-serif">davecb@spamcop.net</a><br></span></div>
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<div><p>A million years ago (roughly around Solaris 9), Sun was suffering from the same problems in measuring their dispatcher as you are with "sloshing".</p><p>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 <i>maybe</i> 10.1, if the sampler happened to sample right when the spike was happening.</p><p>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.<br></p><p>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.</p><p>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.</p><p>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.</p><p>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.</p><p>There was an effort to do kstats in Linux[2], but it had supposedly poor performance, and actual trouble when the clock frequency changed.<br></p><p>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?</p><p>--dave<br></p><p><br></p><p>References:</p>
<ol>
<li>Solaris: <a href="https://can01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fdtrace.org%2Fblogs%2Feschrock%2F2004%2F10%2F13%2Fmicrostate-accounting-in-solaris-10%2F&data=04%7C01%7C%7C7f7cd5aab2ca42e2e7e908d92d25e27f%7Cb07c069022b843668d8d7b845d088e18%7C1%7C0%7C637590463000477252%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=fdZDOtRCcBk%2BO1ksiTOSU%2FltR8IMwueHyj0kQG4UkHw%3D&reserved=0" target="_blank">http://dtrace.org/blogs/eschrock/2004/10/13/microstate-accounting-in-solaris-10/</a><br></li>
<li>A failing Linux effort: <a href="https://can01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flwn.net%2FArticles%2F127296%2F&data=04%7C01%7C%7C7f7cd5aab2ca42e2e7e908d92d25e27f%7Cb07c069022b843668d8d7b845d088e18%7C1%7C0%7C637590463000487248%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=uN0gq8vi0GJHMPpjKVYRjX6G5nQOc%2BugxUwUEk3%2BWJ8%3D&reserved=0" target="_blank">https://lwn.net/Articles/127296/</a>, <a href="https://can01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fsourceforge.net%2Fprojects%2Fmicrostate%2F&data=04%7C01%7C%7C7f7cd5aab2ca42e2e7e908d92d25e27f%7Cb07c069022b843668d8d7b845d088e18%7C1%7C0%7C637590463000497242%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=iMNi40Pl9hMmd1h7WrLFP5jmHQ60mJl7zehhO8miJv4%3D&reserved=0" target="_blank">https://sourceforge.net/projects/microstate/</a><br></li>
</ol>
<pre cols="72" style="font-family:monospace">--
David Collier-Brown, | Always do right. This will gratify
System Programmer and Author | some people and astonish the rest
<a href="mailto:davecb@spamcop.net" target="_blank" style="font-family:monospace">davecb@spamcop.net</a> | -- Mark Twain
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