Sawtooth ping RTT on RPi

Wed May 8 10:12:48 UTC 2013

yup, that looks like two almost-but-not-in-sync sampling periods (one
being poll, one being ping) beating against each other.

Is the USB stuff being polled?

Adrian

On 8 May 2013 02:54, Peter Jeremy <peter at rulingia.com> wrote:
> On 2013-May-08 02:35:06 -0700, Adrian Chadd <adrian at freebsd.org> wrote:
>>On 8 May 2013 01:59, Peter Jeremy <peter at rulingia.com> wrote:
>>> I've noticed a sawtooth-shaped cyclic pattern in ping RTTs to my RPi
>>> (running r249590M):
> ...
>>CAn you run that for a minute or two, just to capture a few cycles?
>
> Apart from the outliers at 0 and 23, the following is a regular
> sawtooth for 2 mins.
>
> PING rpi1.rulingia.com (192.168.123.231): 56 data bytes
> 64 bytes from 192.168.123.231: icmp_seq=0 ttl=64 time=19.996 ms
> 64 bytes from 192.168.123.231: icmp_seq=1 ttl=64 time=10.306 ms
> 64 bytes from 192.168.123.231: icmp_seq=2 ttl=64 time=9.342 ms
> 64 bytes from 192.168.123.231: icmp_seq=3 ttl=64 time=8.361 ms
> 64 bytes from 192.168.123.231: icmp_seq=4 ttl=64 time=7.365 ms
> 64 bytes from 192.168.123.231: icmp_seq=5 ttl=64 time=6.491 ms
> 64 bytes from 192.168.123.231: icmp_seq=6 ttl=64 time=5.477 ms
> 64 bytes from 192.168.123.231: icmp_seq=7 ttl=64 time=4.507 ms
> 64 bytes from 192.168.123.231: icmp_seq=8 ttl=64 time=3.590 ms
> 64 bytes from 192.168.123.231: icmp_seq=9 ttl=64 time=2.537 ms
> 64 bytes from 192.168.123.231: icmp_seq=10 ttl=64 time=1.627 ms
> 64 bytes from 192.168.123.231: icmp_seq=11 ttl=64 time=10.738 ms
> 64 bytes from 192.168.123.231: icmp_seq=12 ttl=64 time=9.709 ms
> 64 bytes from 192.168.123.231: icmp_seq=13 ttl=64 time=8.708 ms
> 64 bytes from 192.168.123.231: icmp_seq=14 ttl=64 time=7.790 ms
> 64 bytes from 192.168.123.231: icmp_seq=15 ttl=64 time=6.832 ms
> 64 bytes from 192.168.123.231: icmp_seq=16 ttl=64 time=5.853 ms
> 64 bytes from 192.168.123.231: icmp_seq=17 ttl=64 time=4.928 ms
> 64 bytes from 192.168.123.231: icmp_seq=18 ttl=64 time=2.948 ms
> 64 bytes from 192.168.123.231: icmp_seq=19 ttl=64 time=2.027 ms
> 64 bytes from 192.168.123.231: icmp_seq=20 ttl=64 time=1.015 ms
> 64 bytes from 192.168.123.231: icmp_seq=21 ttl=64 time=10.042 ms
> 64 bytes from 192.168.123.231: icmp_seq=22 ttl=64 time=9.156 ms
> 64 bytes from 192.168.123.231: icmp_seq=23 ttl=64 time=18.039 ms
> 64 bytes from 192.168.123.231: icmp_seq=24 ttl=64 time=7.217 ms
> 64 bytes from 192.168.123.231: icmp_seq=25 ttl=64 time=6.196 ms
> 64 bytes from 192.168.123.231: icmp_seq=26 ttl=64 time=5.287 ms
> 64 bytes from 192.168.123.231: icmp_seq=27 ttl=64 time=4.321 ms
> 64 bytes from 192.168.123.231: icmp_seq=28 ttl=64 time=3.350 ms
> 64 bytes from 192.168.123.231: icmp_seq=29 ttl=64 time=2.440 ms
> 64 bytes from 192.168.123.231: icmp_seq=30 ttl=64 time=1.385 ms
> 64 bytes from 192.168.123.231: icmp_seq=31 ttl=64 time=10.386 ms
> 64 bytes from 192.168.123.231: icmp_seq=32 ttl=64 time=9.469 ms
> 64 bytes from 192.168.123.231: icmp_seq=33 ttl=64 time=8.527 ms
> 64 bytes from 192.168.123.231: icmp_seq=34 ttl=64 time=7.161 ms
> 64 bytes from 192.168.123.231: icmp_seq=35 ttl=64 time=6.565 ms
> 64 bytes from 192.168.123.231: icmp_seq=36 ttl=64 time=5.629 ms
> 64 bytes from 192.168.123.231: icmp_seq=37 ttl=64 time=4.205 ms
> 64 bytes from 192.168.123.231: icmp_seq=38 ttl=64 time=3.697 ms
> 64 bytes from 192.168.123.231: icmp_seq=39 ttl=64 time=2.720 ms
> 64 bytes from 192.168.123.231: icmp_seq=40 ttl=64 time=1.748 ms
> 64 bytes from 192.168.123.231: icmp_seq=41 ttl=64 time=0.851 ms
> 64 bytes from 192.168.123.231: icmp_seq=42 ttl=64 time=9.869 ms
> 64 bytes from 192.168.123.231: icmp_seq=43 ttl=64 time=8.913 ms
> 64 bytes from 192.168.123.231: icmp_seq=44 ttl=64 time=6.915 ms
> 64 bytes from 192.168.123.231: icmp_seq=45 ttl=64 time=4.986 ms
> 64 bytes from 192.168.123.231: icmp_seq=46 ttl=64 time=4.045 ms
> 64 bytes from 192.168.123.231: icmp_seq=47 ttl=64 time=3.069 ms
> 64 bytes from 192.168.123.231: icmp_seq=48 ttl=64 time=2.137 ms
> 64 bytes from 192.168.123.231: icmp_seq=49 ttl=64 time=1.168 ms
> 64 bytes from 192.168.123.231: icmp_seq=50 ttl=64 time=10.172 ms
> 64 bytes from 192.168.123.231: icmp_seq=51 ttl=64 time=9.254 ms
> 64 bytes from 192.168.123.231: icmp_seq=52 ttl=64 time=8.272 ms
> 64 bytes from 192.168.123.231: icmp_seq=53 ttl=64 time=7.328 ms
> 64 bytes from 192.168.123.231: icmp_seq=54 ttl=64 time=6.375 ms
> 64 bytes from 192.168.123.231: icmp_seq=55 ttl=64 time=5.390 ms
> 64 bytes from 192.168.123.231: icmp_seq=56 ttl=64 time=4.037 ms
> 64 bytes from 192.168.123.231: icmp_seq=57 ttl=64 time=3.425 ms
> 64 bytes from 192.168.123.231: icmp_seq=58 ttl=64 time=2.435 ms
> 64 bytes from 192.168.123.231: icmp_seq=59 ttl=64 time=1.542 ms
> 64 bytes from 192.168.123.231: icmp_seq=60 ttl=64 time=10.591 ms
> 64 bytes from 192.168.123.231: icmp_seq=61 ttl=64 time=9.581 ms
> 64 bytes from 192.168.123.231: icmp_seq=62 ttl=64 time=8.686 ms
> 64 bytes from 192.168.123.231: icmp_seq=63 ttl=64 time=7.721 ms
> 64 bytes from 192.168.123.231: icmp_seq=64 ttl=64 time=6.804 ms
> 64 bytes from 192.168.123.231: icmp_seq=65 ttl=64 time=5.764 ms
> 64 bytes from 192.168.123.231: icmp_seq=66 ttl=64 time=4.777 ms
> 64 bytes from 192.168.123.231: icmp_seq=67 ttl=64 time=3.857 ms
> 64 bytes from 192.168.123.231: icmp_seq=68 ttl=64 time=2.934 ms
> 64 bytes from 192.168.123.231: icmp_seq=69 ttl=64 time=0.928 ms
> 64 bytes from 192.168.123.231: icmp_seq=70 ttl=64 time=9.007 ms
> 64 bytes from 192.168.123.231: icmp_seq=71 ttl=64 time=8.053 ms
> 64 bytes from 192.168.123.231: icmp_seq=72 ttl=64 time=7.651 ms
> 64 bytes from 192.168.123.231: icmp_seq=73 ttl=64 time=6.105 ms
> 64 bytes from 192.168.123.231: icmp_seq=74 ttl=64 time=5.113 ms
> 64 bytes from 192.168.123.231: icmp_seq=75 ttl=64 time=4.188 ms
> 64 bytes from 192.168.123.231: icmp_seq=76 ttl=64 time=3.270 ms
> 64 bytes from 192.168.123.231: icmp_seq=77 ttl=64 time=2.271 ms
> 64 bytes from 192.168.123.231: icmp_seq=78 ttl=64 time=1.284 ms
> 64 bytes from 192.168.123.231: icmp_seq=79 ttl=64 time=1.263 ms
> 64 bytes from 192.168.123.231: icmp_seq=80 ttl=64 time=10.384 ms
> 64 bytes from 192.168.123.231: icmp_seq=81 ttl=64 time=9.392 ms
> 64 bytes from 192.168.123.231: icmp_seq=82 ttl=64 time=8.461 ms
> 64 bytes from 192.168.123.231: icmp_seq=83 ttl=64 time=7.516 ms
> 64 bytes from 192.168.123.231: icmp_seq=84 ttl=64 time=6.152 ms
> 64 bytes from 192.168.123.231: icmp_seq=85 ttl=64 time=5.575 ms
> 64 bytes from 192.168.123.231: icmp_seq=86 ttl=64 time=4.635 ms
> 64 bytes from 192.168.123.231: icmp_seq=87 ttl=64 time=3.626 ms
> 64 bytes from 192.168.123.231: icmp_seq=88 ttl=64 time=2.728 ms
> 64 bytes from 192.168.123.231: icmp_seq=89 ttl=64 time=1.751 ms
> 64 bytes from 192.168.123.231: icmp_seq=90 ttl=64 time=0.758 ms
> 64 bytes from 192.168.123.231: icmp_seq=91 ttl=64 time=9.798 ms
> 64 bytes from 192.168.123.231: icmp_seq=92 ttl=64 time=8.824 ms
> 64 bytes from 192.168.123.231: icmp_seq=93 ttl=64 time=7.890 ms
> 64 bytes from 192.168.123.231: icmp_seq=94 ttl=64 time=6.932 ms
> 64 bytes from 192.168.123.231: icmp_seq=95 ttl=64 time=4.977 ms
> 64 bytes from 192.168.123.231: icmp_seq=96 ttl=64 time=4.015 ms
> 64 bytes from 192.168.123.231: icmp_seq=97 ttl=64 time=3.049 ms
> 64 bytes from 192.168.123.231: icmp_seq=98 ttl=64 time=2.093 ms
> 64 bytes from 192.168.123.231: icmp_seq=99 ttl=64 time=1.111 ms
> 64 bytes from 192.168.123.231: icmp_seq=100 ttl=64 time=10.213 ms
> 64 bytes from 192.168.123.231: icmp_seq=101 ttl=64 time=9.263 ms
> 64 bytes from 192.168.123.231: icmp_seq=102 ttl=64 time=8.283 ms
> 64 bytes from 192.168.123.231: icmp_seq=103 ttl=64 time=8.312 ms
> 64 bytes from 192.168.123.231: icmp_seq=104 ttl=64 time=7.379 ms
> 64 bytes from 192.168.123.231: icmp_seq=105 ttl=64 time=6.411 ms
> 64 bytes from 192.168.123.231: icmp_seq=106 ttl=64 time=5.409 ms
> 64 bytes from 192.168.123.231: icmp_seq=107 ttl=64 time=4.457 ms
> 64 bytes from 192.168.123.231: icmp_seq=108 ttl=64 time=3.472 ms
> 64 bytes from 192.168.123.231: icmp_seq=109 ttl=64 time=2.561 ms
> 64 bytes from 192.168.123.231: icmp_seq=110 ttl=64 time=1.598 ms
> 64 bytes from 192.168.123.231: icmp_seq=111 ttl=64 time=10.610 ms
> 64 bytes from 192.168.123.231: icmp_seq=112 ttl=64 time=9.636 ms
> 64 bytes from 192.168.123.231: icmp_seq=113 ttl=64 time=8.659 ms
> 64 bytes from 192.168.123.231: icmp_seq=114 ttl=64 time=7.661 ms
> 64 bytes from 192.168.123.231: icmp_seq=115 ttl=64 time=6.762 ms
> 64 bytes from 192.168.123.231: icmp_seq=116 ttl=64 time=5.771 ms
> 64 bytes from 192.168.123.231: icmp_seq=117 ttl=64 time=4.816 ms
> 64 bytes from 192.168.123.231: icmp_seq=118 ttl=64 time=3.888 ms
> 64 bytes from 192.168.123.231: icmp_seq=119 ttl=64 time=2.909 ms
> 64 bytes from 192.168.123.231: icmp_seq=120 ttl=64 time=0.936 ms
> ^C
> --- rpi1.rulingia.com ping statistics ---
> 121 packets transmitted, 121 packets received, 0.0% packet loss
> round-trip min/avg/max/stddev = 0.758/5.921/19.996/3.362 ms
>
> --
> Peter Jeremy