From: Caleb Cushing <xenoterracide@gmail.com>
To: Neil Davies <neil.davies@pnsol.com>
Cc: Hal Murray <hmurray@megapathdsl.net>, bloat@lists.bufferbloat.net
Subject: Re: [Bloat] Steam In Home Streaming on ath9k wifi
Date: Sun, 26 Nov 2017 07:25:36 +0000 [thread overview]
Message-ID: <CAAHKNRH0s+i++SRmeLk6U9sei_6k4Z_=dZsii8+GRbtrnOm4ww@mail.gmail.com> (raw)
In-Reply-To: <AB261D18-7F22-4B61-884D-8018C8A12598@pnsol.com>
[-- Attachment #1: Type: text/plain, Size: 8617 bytes --]
ping from laptop
C:\Users\xeno>ping 192.168.1.105 -n 100
Pinging 192.168.1.105 with 32 bytes of data:
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=4ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=4ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=4ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=4ms TTL=128
Reply from 192.168.1.105: bytes=32 time=4ms TTL=128
Reply from 192.168.1.105: bytes=32 time=4ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=4ms TTL=128
Reply from 192.168.1.105: bytes=32 time=4ms TTL=128
Reply from 192.168.1.105: bytes=32 time=4ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=4ms TTL=128
Reply from 192.168.1.105: bytes=32 time=4ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=4ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=4ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=4ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=4ms TTL=128
Reply from 192.168.1.105: bytes=32 time=4ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=4ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=4ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=4ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=4ms TTL=128
Reply from 192.168.1.105: bytes=32 time=4ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=4ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=4ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=5ms TTL=128
Reply from 192.168.1.105: bytes=32 time=4ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=4ms TTL=128
Reply from 192.168.1.105: bytes=32 time=4ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=4ms TTL=128
Reply from 192.168.1.105: bytes=32 time=4ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=4ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=4ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=4ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=4ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=4ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Reply from 192.168.1.105: bytes=32 time=4ms TTL=128
Reply from 192.168.1.105: bytes=32 time=3ms TTL=128
Ping statistics for 192.168.1.105:
Packets: Sent = 100, Received = 100, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 3ms, Maximum = 5ms, Average = 3ms
On Fri, Nov 24, 2017 at 3:35 AM Neil Davies <neil.davies@pnsol.com> wrote:
> On 24 Nov 2017, at 09:20, Hal Murray <hmurray@megapathdsl.net> wrote:
>
>
> neil.davies@pnsol.com said:
>
> There are a few more issues - the relative drift between the two clocks
> can be as high as 200ppm, though typically 50-75ppm is what we observe, but
> this drift is monotonic.
>
>
> 200 ppm seems pretty high, but not off scale. If ntpd is running and not
> getting confused by long queuing delays, it should correct the drift to
> well
> under 1 ppm. If you turn on loopstats, you can graph it.
>
>
> I’m saying that is the maximum rate of drift between two clocks even
> when they are under NTP control. As you say below the clock rates
> are not completely stable they are temperature dependent.
> When we did this with the guys at CERN we could
> correlate the results with the workload (see below for references).
>
> We’ve got ~1M experiments using this approach across various networks,
> the numbers are what we are seeing in practice.
>
> The caveat is that, after a while (i.e several 100s) the clock drift can
> make
> a significant difference (i.e a few ms) in the one-way delay estimation.
>
>
> If you are blasting the network and adding long queuing delays, ntpd can
> easily get confused.
>
> There is another quirk to keep in mind. The temperature coefficient of
> the
> crystal is ballpark of 1 ppm per C. Things can change significantly if an
> idle system starts flinging lots of bits around.
>
>
> Also NTP can make changes at one (or both) ends - they show up as distinct
> direction changes in the drift.
>
>
> I'm not sure what you mean by "direction change". I'd expect a graph of
> the
> time offset vs time to be linear and the slope would have a sharp change
> if
> ntpd changed it's "drift" correction and/or maybe a rounded bend as a
> system
> warmed up.
>
>
> Don’t forget you are measuring the difference in the rates between two NTP
> clocks,
> hence the change when one of the NTP systems decides to change the drift
> rate
> the relative rate can change direction.
>
>
> ----------
>
> Are you happy with whatever you are doing? Should we try to set things
> up
>
> so ntpd works well enough? How close would you like the times to be? …
>
>
> Yep, we’re very happy - we don’t care that there is a linear clock drift
> (we
> can correct for that) and the step changes are infrequent and can be
> eliminated
> from the long term analysis.
>
> You might find §4.4 (esp §4.4.5) and §5.6 in
> https://cds.cern.ch/record/1504817/files/CERN-THESIS-2013-004.pdf
> interesting. It illustrates these sort of issues.
>
>
>
>
>
> --
> These are my opinions. I hate spam.
>
>
>
>
> _______________________________________________
> Bloat mailing list
> Bloat@lists.bufferbloat.net
> https://lists.bufferbloat.net/listinfo/bloat
>
--
Caleb Cushing
http://xenoterracide.com
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next prev parent reply other threads:[~2017-11-26 7:25 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-21 19:08 Hal Murray
2017-11-22 10:31 ` Neil Davies
2017-11-23 17:48 ` Caleb Cushing
2017-11-24 9:20 ` Hal Murray
2017-11-24 9:34 ` Neil Davies
2017-11-26 7:25 ` Caleb Cushing [this message]
2017-11-26 7:29 ` Caleb Cushing
2017-11-26 7:55 ` Jan Ceuleers
2017-11-26 10:05 ` Jonathan Morton
2017-11-26 10:53 ` Jan Ceuleers
2017-11-26 10:55 ` Jonathan Morton
2017-11-26 11:54 ` Steinar H. Gunderson
2017-11-26 13:03 ` Jan Ceuleers
2017-11-26 13:05 ` Jan Ceuleers
2017-11-26 13:13 ` Steinar H. Gunderson
2017-11-26 17:53 ` Dave Taht
2017-11-26 18:43 ` Jan Ceuleers
2017-11-26 23:11 ` Dave Taht
2017-12-04 7:24 ` Caleb Cushing
-- strict thread matches above, loose matches on Subject: below --
2017-11-18 22:14 Caleb Cushing
2017-11-19 16:28 ` Toke Høiland-Jørgensen
2017-11-19 21:18 ` Caleb Cushing
2017-11-19 21:27 ` Toke Høiland-Jørgensen
2017-11-19 22:03 ` Caleb Cushing
2017-11-19 22:13 ` Dave Taht
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