Re: Strange network behaviour

Simon Gao
2007-12-05T18:05:31Z

Mike wrote:
> Avi Kivity schrieb:
>
>> Mike wrote:
>>
>>> Sure,
>>> here the ping results from the host to the guest atm of the peaks:
>>> 64 bytes from postfix (195.24.77.173): icmp_seq=347 ttl=64 time=10.6 ms
>>> 64 bytes from postfix (195.24.77.173): icmp_seq=348 ttl=64 time=11.6 ms
>>> 64 bytes from postfix (195.24.77.173): icmp_seq=349 ttl=64 time=11.6 ms
>>> 64 bytes from postfix (195.24.77.173): icmp_seq=350 ttl=64 time=465 ms
>>> 64 bytes from postfix (195.24.77.173): icmp_seq=351 ttl=64 time=455 ms
>>> 64 bytes from postfix (195.24.77.173): icmp_seq=352 ttl=64 time=349 ms
>>> 64 bytes from postfix (195.24.77.173): icmp_seq=353 ttl=64 time=314 ms
>>> 64 bytes from postfix (195.24.77.173): icmp_seq=354 ttl=64 time=483 ms
>>> 64 bytes from postfix (195.24.77.173): icmp_seq=355 ttl=64 time=871 ms
>>> 64 bytes from postfix (195.24.77.173): icmp_seq=357 ttl=64 time=1889 ms
>>> 64 bytes from postfix (195.24.77.173): icmp_seq=358 ttl=64 time=1635 ms
>>> 64 bytes from postfix (195.24.77.173): icmp_seq=359 ttl=64 time=1973 ms
>>> 64 bytes from postfix (195.24.77.173): icmp_seq=360 ttl=64 time=1796 ms
>>> 64 bytes from postfix (195.24.77.173): icmp_seq=361 ttl=64 time=1961 ms
>>> 64 bytes from postfix (195.24.77.173): icmp_seq=362 ttl=64 time=2029 ms
>>> 64 bytes from postfix (195.24.77.173): icmp_seq=363 ttl=64 time=1994 ms
>>> 64 bytes from postfix (195.24.77.173): icmp_seq=364 ttl=64 time=1689 ms
>>> 64 bytes from postfix (195.24.77.173): icmp_seq=365 ttl=64 time=932 ms
>>> 64 bytes from postfix (195.24.77.173): icmp_seq=366 ttl=64 time=899 ms
>>> 64 bytes from postfix (195.24.77.173): icmp_seq=367 ttl=64 time=752 ms
>>> 64 bytes from postfix (195.24.77.173): icmp_seq=368 ttl=64 time=860 ms
>>> 64 bytes from postfix (195.24.77.173): icmp_seq=369 ttl=64 time=483 ms
>>> 64 bytes from postfix (195.24.77.173): icmp_seq=370 ttl=64 time=244 ms
>>> 64 bytes from postfix (195.24.77.173): icmp_seq=371 ttl=64 time=7.89 ms
>>> 64 bytes from postfix (195.24.77.173): icmp_seq=372 ttl=64 time=5.98 ms
>>> 64 bytes from postfix (195.24.77.173): icmp_seq=373 ttl=64 time=6.31 ms
>>>
>>> The peaks started @ +/- 14:53:39 and ended @ +/- 14:53:59
>>> You can download the trace file at:
>>> http://www.eliteserver.biz/trace2.tar.gz
>>>
>>>
>>>
>>>
>> The traces show that the periods of latency correspond to floods of
>> broadcast packets on the network
>>
>>
>>> 10 29895 14:53:25
>>> 9 29895 14:53:26
>>> 9 29895 14:53:27
>>> 9 29895 14:53:28
>>> 16 29895 14:53:29
>>> 19 29895 14:53:30
>>> 19 29895 14:53:31
>>> 14 29895 14:53:32
>>> 13 29895 14:53:33
>>> 12 29895 14:53:34
>>> 205 29895 14:53:35
>>> 203 29895 14:53:36
>>> 276 29895 14:53:37
>>> 234 29895 14:53:38
>>> 234 29895 14:53:39
>>> 243 29895 14:53:40
>>> 234 29895 14:53:41
>>> 259 29895 14:53:42
>>> 228 29895 14:53:43
>>> 325 29895 14:53:44
>>> 242 29895 14:53:45
>>> 271 29895 14:53:46
>>> 251 29895 14:53:47
>>> 227 29895 14:53:48
>>> 178 29895 14:53:49
>>> 166 29895 14:53:50
>>> 271 29895 14:53:51
>>> 244 29895 14:53:52
>>> 287 29895 14:53:53
>>> 196 29895 14:53:54
>>> 215 29895 14:53:55
>>> 83 29895 14:53:56
>>> 65 29895 14:53:57
>>> 10 29895 14:53:58
>>> 9 29895 14:53:59
>>> 10 29895 14:54:00
>>> 14 29895 14:54:01
>>> 14 29895 14:54:02
>>> 12 29895 14:54:03
>>> 13 29895 14:54:04
>>> 16 29895 14:54:05
>>>
>> The first column is the number of packets delivered at the time in the
>> third column. The broadcast packets are clearly visible in the trace
>> as having \xff in the first 6 bytes of the packet. The ping packet is
>> getting queued behind the broadcasts and thus delayed.
>>
>> However, kvm is capable of much more than 200 packets/sec. I get
>> about 6500 here with a flood ping. Can you try this on the host:
>>
>> ping -f -q guest-ip
>>
>> Hit ctrl-C after a second or two and send the output.
>>
>> You can also try running wireshark on the host to capture the
>> broadcast packets. Maybe they cause some processing on the guest and
>> slow it down.
>>
>>
> 9066 packets transmitted, 9055 received, 0% packet loss, time 1956ms
> rtt min/avg/max/mdev = 0.078/0.171/16.659/0.181 ms, pipe 2, ipg/ewma
> 0.215/0.213 ms
>
> The same time a tried a ping over the internet. No peaks.
>
> I also tried over a longer time, no peaks.
>
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I also saw the similar problem. However, it happens with I have several
KVM guests running and sharing the same network bridge. If just one
single KVM guest, then everything works fine.

Simon