High ping time from domU , normal time when tcpdump is running

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High ping time from domU , normal time when tcpdump is running

by Javier Barroso-3 :: Rate this Message:

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HI,

I'm having trouble with a debian etch HVM domU inside a dom0 domu

>From domU, I try to ping gateway, but response time change if tcpdump
is writing to standard output. Ping without tcpdump running has a 4 ms
time.

While tcpdump is writing in stdout, in another terminal:
# ping -n -c20 10.12.6.1
PING 10.12.6.1 (10.12.6.1) 56(84) bytes of data.
64 bytes from 10.12.6.1: icmp_seq=1 ttl=64 time=0.448 ms
64 bytes from 10.12.6.1: icmp_seq=2 ttl=64 time=0.421 ms
64 bytes from 10.12.6.1: icmp_seq=3 ttl=64 time=0.405 ms
64 bytes from 10.12.6.1: icmp_seq=4 ttl=64 time=0.418 ms
64 bytes from 10.12.6.1: icmp_seq=5 ttl=64 time=0.423 ms
64 bytes from 10.12.6.1: icmp_seq=6 ttl=64 time=0.414 ms
64 bytes from 10.12.6.1: icmp_seq=7 ttl=64 time=0.411 ms
64 bytes from 10.12.6.1: icmp_seq=8 ttl=64 time=0.400 ms
64 bytes from 10.12.6.1: icmp_seq=9 ttl=64 time=0.427 ms
64 bytes from 10.12.6.1: icmp_seq=10 ttl=64 time=0.408 ms
64 bytes from 10.12.6.1: icmp_seq=11 ttl=64 time=0.461 ms
64 bytes from 10.12.6.1: icmp_seq=12 ttl=64 time=0.420 ms
64 bytes from 10.12.6.1: icmp_seq=13 ttl=64 time=0.389 ms
64 bytes from 10.12.6.1: icmp_seq=14 ttl=64 time=0.424 ms
64 bytes from 10.12.6.1: icmp_seq=15 ttl=64 time=0.412 ms
64 bytes from 10.12.6.1: icmp_seq=16 ttl=64 time=0.398 ms
64 bytes from 10.12.6.1: icmp_seq=17 ttl=64 time=0.388 ms
64 bytes from 10.12.6.1: icmp_seq=18 ttl=64 time=0.403 ms
64 bytes from 10.12.6.1: icmp_seq=19 ttl=64 time=0.413 ms
64 bytes from 10.12.6.1: icmp_seq=20 ttl=64 time=0.404 ms

--- 10.12.6.1 ping statistics ---
20 packets transmitted, 20 received, 0% packet loss, time 19000ms
rtt min/avg/max/mdev = 0.388/0.414/0.461/0.024 ms


With tcpdump -wfile icmp in one terminal and ping in another:
# ping -n -c20 10.12.6.1
PING 10.12.6.1 (10.12.6.1) 56(84) bytes of data.
64 bytes from 10.12.6.1: icmp_seq=1 ttl=64 time=2.35 ms
64 bytes from 10.12.6.1: icmp_seq=2 ttl=64 time=4.11 ms
64 bytes from 10.12.6.1: icmp_seq=3 ttl=64 time=4.12 ms
64 bytes from 10.12.6.1: icmp_seq=4 ttl=64 time=4.16 ms
64 bytes from 10.12.6.1: icmp_seq=5 ttl=64 time=4.16 ms
64 bytes from 10.12.6.1: icmp_seq=6 ttl=64 time=0.398 ms
64 bytes from 10.12.6.1: icmp_seq=7 ttl=64 time=4.18 ms
64 bytes from 10.12.6.1: icmp_seq=8 ttl=64 time=4.16 ms
64 bytes from 10.12.6.1: icmp_seq=9 ttl=64 time=4.16 ms
64 bytes from 10.12.6.1: icmp_seq=10 ttl=64 time=4.15 ms
64 bytes from 10.12.6.1: icmp_seq=11 ttl=64 time=4.15 ms
64 bytes from 10.12.6.1: icmp_seq=12 ttl=64 time=4.15 ms
64 bytes from 10.12.6.1: icmp_seq=13 ttl=64 time=4.19 ms
64 bytes from 10.12.6.1: icmp_seq=14 ttl=64 time=4.16 ms
64 bytes from 10.12.6.1: icmp_seq=15 ttl=64 time=4.16 ms
64 bytes from 10.12.6.1: icmp_seq=16 ttl=64 time=4.16 ms
64 bytes from 10.12.6.1: icmp_seq=17 ttl=64 time=4.15 ms
64 bytes from 10.12.6.1: icmp_seq=18 ttl=64 time=4.14 ms
64 bytes from 10.12.6.1: icmp_seq=19 ttl=64 time=4.18 ms
64 bytes from 10.12.6.1: icmp_seq=20 ttl=64 time=4.15 ms

--- 10.12.6.1 ping statistics ---
20 packets transmitted, 20 received, 0% packet loss, time 19003ms
rtt min/avg/max/mdev = 0.398/3.881/4.197/0.893 ms

Without any tcpdump running:
# ping -n -c20 10.12.6.1
PING 10.12.6.1 (10.12.6.1) 56(84) bytes of data.
64 bytes from 10.12.6.1: icmp_seq=1 ttl=64 time=1.26 ms
64 bytes from 10.12.6.1: icmp_seq=2 ttl=64 time=4.13 ms
64 bytes from 10.12.6.1: icmp_seq=3 ttl=64 time=4.16 ms
64 bytes from 10.12.6.1: icmp_seq=4 ttl=64 time=4.16 ms
64 bytes from 10.12.6.1: icmp_seq=5 ttl=64 time=4.16 ms
64 bytes from 10.12.6.1: icmp_seq=6 ttl=64 time=4.00 ms
64 bytes from 10.12.6.1: icmp_seq=7 ttl=64 time=4.16 ms
64 bytes from 10.12.6.1: icmp_seq=8 ttl=64 time=4.13 ms
64 bytes from 10.12.6.1: icmp_seq=9 ttl=64 time=4.16 ms
64 bytes from 10.12.6.1: icmp_seq=10 ttl=64 time=4.15 ms
64 bytes from 10.12.6.1: icmp_seq=11 ttl=64 time=4.16 ms
64 bytes from 10.12.6.1: icmp_seq=12 ttl=64 time=4.16 ms
64 bytes from 10.12.6.1: icmp_seq=13 ttl=64 time=4.16 ms
64 bytes from 10.12.6.1: icmp_seq=14 ttl=64 time=4.13 ms
64 bytes from 10.12.6.1: icmp_seq=15 ttl=64 time=4.15 ms
64 bytes from 10.12.6.1: icmp_seq=16 ttl=64 time=4.16 ms
64 bytes from 10.12.6.1: icmp_seq=17 ttl=64 time=4.16 ms
64 bytes from 10.12.6.1: icmp_seq=18 ttl=64 time=4.16 ms
64 bytes from 10.12.6.1: icmp_seq=19 ttl=64 time=4.16 ms
64 bytes from 10.12.6.1: icmp_seq=20 ttl=64 time=4.12 ms

--- 10.12.6.1 ping statistics ---
20 packets transmitted, 20 received, 0% packet loss, time 19002ms
rtt min/avg/max/mdev = 1.260/4.003/4.164/0.630 ms

Could be a cpu issue ? I think no because uptime tells:
load average: 0.24, 0.16, 0.18
and nice -n20 doesn't help here.

But I read about cpu won't dedicate enought time to network card ..

I can't get my domU with two cpus, does it should works ?

dom0 # grep cpu|net /etc/xen/domU
vcpus=2
cpus = "1,2"


dom0# xm vcpu-list domU
Name                              ID VCPUs   CPU State   Time(s) CPU Affinity
domU                             4     0     3   -b-   23103.3 1-4
domU                             4     1     -   --p       0.0 1-4

dom0 # dpkg -l | grep xen
...
ii  xen-linux-system-2.6.18-6-xen-amd64 2.6.18.dfsg.1-24etch4 XEN
system with Linux 2.6.18 image on AMD64
ii  xen-ioemu-3.0.3-1                   3.0.3-0-4             XEN
administrative tools
ii  xen-hypervisor-3.0.3-1-amd64        3.0.3-0-4             The Xen
Hypervisor on AMD64

domU# # ethtool -i eth0
driver: 8139cp
version: 1.2
firmware-version:
bus-info: 0000:00:04.0

domU# uname -a
Linux domU 2.6.18-6-686 #1 SMP Sat Dec 27 09:31:05 UTC 2008 i686 GNU/Linux
# cat /proc/cpuinfo
processor : 0
vendor_id : GenuineIntel
cpu family : 6
model : 15
model name : Intel(R) Xeon(R) CPU           L5310  @ 1.60GHz
stepping : 7
cpu MHz : 1596.067
cache size : 4096 KB
fdiv_bug : no
hlt_bug : no
f00f_bug : no
coma_bug : no
fpu : yes
fpu_exception : yes
cpuid level : 10
wp : yes
flags : fpu vme de pse tsc msr mce cx8 sep mtrr pge mca cmov pat
clflush dts mmx fxsr sse sse2 ss pbe syscall nx lm constant_tsc up pni
ds_cpl cx16 xtpr lahf_lm
bogomips : 3198.72

Could be a interrupts?
I don't known how study that :(
I post cat /proc/interrupts (maybe it can help ?)

# cat /proc/interrupts
           CPU0
  0:   37770417          XT-PIC  timer
  1:          9          XT-PIC  i8042
  2:          0          XT-PIC  cascade
 11:    2847259          XT-PIC  eth0
 12:        110          XT-PIC  i8042
 14:     521293          XT-PIC  ide0

Note that I'm having trouble too with other hvm machine which too go
to the pass in the time and keep hangs with black screen when I try to
connect to vnc and I have to turn off and turn on it. I'm thinking in
go to paravirtualization both machines.
I tried playing with acpi=off and noapic as kernel parameters but
nothing happens

Any pointer ?

Thanks !

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