Openmoko Bug #2320: icmp ping RTT over wifi plotted over time forms a sawtooth wave
Openmoko Public Trac
bugs at docs.openmoko.org
Wed Nov 25 22:57:05 CET 2009
#2320: icmp ping RTT over wifi plotted over time forms a sawtooth wave
-----------------------------+----------------------------------------------
Reporter: lindi | Owner: openmoko-kernel
Type: defect | Status: new
Priority: normal | Milestone:
Component: System Software | Version: unspecified
Severity: normal | Keywords: wifi latency kernel
Haspatch: 0 | Blockedby:
Estimated: | Patchreview:
Blocking: | Reproducible: always
-----------------------------+----------------------------------------------
icmp ping over wifi seems to show very peculiar delays that increase by
around 10 ms on every attempt and at some point reset back to 20 ms:
{{{
$ ping 192.168.2.1
64 bytes from 192.168.2.1: icmp_seq=29 ttl=64 time=20.1 ms
64 bytes from 192.168.2.1: icmp_seq=30 ttl=64 time=40.1 ms
64 bytes from 192.168.2.1: icmp_seq=31 ttl=64 time=60.1 ms
64 bytes from 192.168.2.1: icmp_seq=32 ttl=64 time=80.3 ms
64 bytes from 192.168.2.1: icmp_seq=33 ttl=64 time=90.3 ms
64 bytes from 192.168.2.1: icmp_seq=34 ttl=64 time=110 ms
64 bytes from 192.168.2.1: icmp_seq=35 ttl=64 time=30.1 ms
64 bytes from 192.168.2.1: icmp_seq=36 ttl=64 time=50.1 ms
64 bytes from 192.168.2.1: icmp_seq=37 ttl=64 time=70.1 ms
64 bytes from 192.168.2.1: icmp_seq=38 ttl=64 time=90.2 ms
64 bytes from 192.168.2.1: icmp_seq=39 ttl=64 time=109 ms
64 bytes from 192.168.2.1: icmp_seq=40 ttl=64 time=20.1 ms
64 bytes from 192.168.2.1: icmp_seq=41 ttl=64 time=40.1 ms
64 bytes from 192.168.2.1: icmp_seq=42 ttl=64 time=60.1 ms
64 bytes from 192.168.2.1: icmp_seq=43 ttl=64 time=85.5 ms
64 bytes from 192.168.2.1: icmp_seq=44 ttl=64 time=104 ms
64 bytes from 192.168.2.1: icmp_seq=45 ttl=64 time=115 ms
64 bytes from 192.168.2.1: icmp_seq=46 ttl=64 time=447 ms
64 bytes from 192.168.2.1: icmp_seq=47 ttl=64 time=770 ms
64 bytes from 192.168.2.1: icmp_seq=48 ttl=64 time=380 ms
64 bytes from 192.168.2.1: icmp_seq=49 ttl=64 time=90.2 ms
64 bytes from 192.168.2.1: icmp_seq=50 ttl=64 time=110 ms
64 bytes from 192.168.2.1: icmp_seq=51 ttl=64 time=30.1 ms
64 bytes from 192.168.2.1: icmp_seq=52 ttl=64 time=50.1 ms
64 bytes from 192.168.2.1: icmp_seq=53 ttl=64 time=70.1 ms
64 bytes from 192.168.2.1: icmp_seq=54 ttl=64 time=90.2 ms
64 bytes from 192.168.2.1: icmp_seq=55 ttl=64 time=100 ms
64 bytes from 192.168.2.1: icmp_seq=56 ttl=64 time=21.5 ms
64 bytes from 192.168.2.1: icmp_seq=57 ttl=64 time=40.1 ms
64 bytes from 192.168.2.1: icmp_seq=58 ttl=64 time=60.0 ms
64 bytes from 192.168.2.1: icmp_seq=59 ttl=64 time=80.3 ms
64 bytes from 192.168.2.1: icmp_seq=60 ttl=64 time=100 ms
64 bytes from 192.168.2.1: icmp_seq=61 ttl=64 time=120 ms
64 bytes from 192.168.2.1: icmp_seq=62 ttl=64 time=30.1 ms
64 bytes from 192.168.2.1: icmp_seq=63 ttl=64 time=50.0 ms
64 bytes from 192.168.2.1: icmp_seq=64 ttl=64 time=70.1 ms
64 bytes from 192.168.2.1: icmp_seq=65 ttl=64 time=90.2 ms
64 bytes from 192.168.2.1: icmp_seq=66 ttl=64 time=110 ms
64 bytes from 192.168.2.1: icmp_seq=67 ttl=64 time=30.1 ms
64 bytes from 192.168.2.1: icmp_seq=68 ttl=64 time=50.0 ms
64 bytes from 192.168.2.1: icmp_seq=69 ttl=64 time=60.0 ms
64 bytes from 192.168.2.1: icmp_seq=70 ttl=64 time=80.3 ms
64 bytes from 192.168.2.1: icmp_seq=71 ttl=64 time=100 ms
64 bytes from 192.168.2.1: icmp_seq=72 ttl=64 time=20.1 ms
64 bytes from 192.168.2.1: icmp_seq=73 ttl=64 time=40.1 ms
64 bytes from 192.168.2.1: icmp_seq=74 ttl=64 time=60.1 ms
}}}
linux is andy-tracking a3587e4ed77974ad
hardware is gta02v5
tested with two WLAN APs, one is wrt54gl v1.1 running openwrt svn r18459
with b43 driver and the other one is unknown.
Is something buffering the packets?
Since ping measures RTT I used
nc -lp1234 -u | perl -e 'use Time::HiRes; $| = 1; while (<>) {
$l=Time::HiRes::time() - $_; $l*=1000;print "$l\n"; }'
perl -e 'use Time::HiRes; $| = 1; while (1) { print Time::HiRes::time() .
"\n"; sleep(1); }' | nc -u 192.168.0.99 1234
to measure delay from PC to openmoko
{{{
12.293959
12.502098
12.347841
11.870050
11.975908
11.922026
12.448931
11.515045
12.295866
11.923933
11.738920
11.603022
11.639023
11.248970
26.214981
11.125946
11.755848
10.733032
11.644983
11.251116
11.290932
11.272812
11.109018
11.723185
11.438990
11.480951
11.324072
11.042976
11.093998
10.823870
14.966869
18.019819
}}}
and openmoko to PC
{{{
128.469002
129.320871
128.603947
128.538143
128.767979
128.843081
136.215937
133.112204
137.031090
128.907930
128.802073
128.696215
128.594887
129.487049
129.377853
129.401934
129.205000
129.066002
128.966105
128.860008
129.772913
129.657042
137.234938
129.427921
129.323017
129.232895
130.115997
130.011093
130.097162
129.807007
129.707109
129.714024
129.505884
}}}
The absolute values mean nothing since the clocks are not entirely in
sync. However, we can see here that this test does not show the same
variations as we see with ping. What an earth could be going on here? If I
ping with shorter interval the delay seems to stick to some value that is
different on each attempt:
{{{
lindi at ginger:~$ ping -i 0.2 192.168.2.1
PING 192.168.2.1 (192.168.2.1) 56(84) bytes of data.
64 bytes from 192.168.2.1: icmp_seq=1 ttl=64 time=87.4 ms
64 bytes from 192.168.2.1: icmp_seq=2 ttl=64 time=90.2 ms
64 bytes from 192.168.2.1: icmp_seq=3 ttl=64 time=90.1 ms
64 bytes from 192.168.2.1: icmp_seq=4 ttl=64 time=90.1 ms
64 bytes from 192.168.2.1: icmp_seq=5 ttl=64 time=90.1 ms
64 bytes from 192.168.2.1: icmp_seq=6 ttl=64 time=90.1 ms
64 bytes from 192.168.2.1: icmp_seq=7 ttl=64 time=90.3 ms
64 bytes from 192.168.2.1: icmp_seq=8 ttl=64 time=90.1 ms
64 bytes from 192.168.2.1: icmp_seq=9 ttl=64 time=90.0 ms
64 bytes from 192.168.2.1: icmp_seq=10 ttl=64 time=90.1 ms
64 bytes from 192.168.2.1: icmp_seq=11 ttl=64 time=90.1 ms
}}}
{{{
lindi at ginger:~$ ping -i 0.2 192.168.2.1
PING 192.168.2.1 (192.168.2.1) 56(84) bytes of data.
64 bytes from 192.168.2.1: icmp_seq=1 ttl=64 time=32.1 ms
64 bytes from 192.168.2.1: icmp_seq=2 ttl=64 time=35.4 ms
64 bytes from 192.168.2.1: icmp_seq=3 ttl=64 time=35.3 ms
64 bytes from 192.168.2.1: icmp_seq=4 ttl=64 time=35.3 ms
64 bytes from 192.168.2.1: icmp_seq=5 ttl=64 time=35.3 ms
64 bytes from 192.168.2.1: icmp_seq=6 ttl=64 time=35.3 ms
64 bytes from 192.168.2.1: icmp_seq=7 ttl=64 time=35.3 ms
64 bytes from 192.168.2.1: icmp_seq=8 ttl=64 time=40.1 ms
64 bytes from 192.168.2.1: icmp_seq=9 ttl=64 time=40.1 ms
}}}
{{{
lindi at ginger:~$ ping -i 0.2 192.168.2.1
PING 192.168.2.1 (192.168.2.1) 56(84) bytes of data.
64 bytes from 192.168.2.1: icmp_seq=1 ttl=64 time=108 ms
64 bytes from 192.168.2.1: icmp_seq=2 ttl=64 time=110 ms
64 bytes from 192.168.2.1: icmp_seq=3 ttl=64 time=110 ms
64 bytes from 192.168.2.1: icmp_seq=4 ttl=64 time=110 ms
64 bytes from 192.168.2.1: icmp_seq=5 ttl=64 time=110 ms
64 bytes from 192.168.2.1: icmp_seq=6 ttl=64 time=110 ms
64 bytes from 192.168.2.1: icmp_seq=7 ttl=64 time=110 ms
64 bytes from 192.168.2.1: icmp_seq=8 ttl=64 time=105 ms
64 bytes from 192.168.2.1: icmp_seq=9 ttl=64 time=110 ms
64 bytes from 192.168.2.1: icmp_seq=10 ttl=64 time=110 ms
64 bytes from 192.168.2.1: icmp_seq=11 ttl=64 time=110 ms
64 bytes from 192.168.2.1: icmp_seq=12 ttl=64 time=110 ms
64 bytes from 192.168.2.1: icmp_seq=13 ttl=64 time=110 ms
}}}
--
Ticket URL: <https://docs.openmoko.org/trac/ticket/2320>
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