[Xen-users] Poor network performance on Dom0 [2.6.18-6-xen-amd64]

["Alejandro Martini" <alejandro.martini@xxxxxxxxx>]

I am experiencing poor network performance on Dom0. When i ping other
hosts on the same LAN, packets are out of order, and they show
response times ranging from < 1 ms to several seconds, and some
packets get lost.

For example, a typical ping result looks like this:

87 packets transmitted, 80 received, +3 errors, 8% packet loss, time 86038ms
rtt min/avg/max/mdev = 0.080/5068.340/12502.274/4207.494 ms, pipe 13

If i listen for icmp traffic from a physical host that is between Dom0
and the one i'm pinging (i.e., on the same LAN), all icmp requests and
replies come and go timely and in perfect order.

However, when i listen for icmp traffic at Dom0 on peth3 (the
interface that is attached to the LAN switch), i can see the same
delays that show up when pinging.

As you can imagine, this problem does not affect only icmp traffic,
but also every tcp-based service running in Dom0 (such as smtp).

Processor load seems fine, and almost never goes above 0.1 (CPU is an
AMD dual-core 4200)

Is there anything that can be done in order to solve this problem? Are
there any known issues related to this kind of setup? (see below the
system configuration details for information about the operating
system, processor, and network adapters).

Another odd beahviour that i've seen on this system, is that when i
check the network adapter (mii-diag peth3), sometimes it shows the
following line:

"Link status: previously broken, but now reestablished."

If I run mii-diag a second time, it says:

"You have link beat, and everything is working OK."

One more thing that doesn't seem quite right is the interrupt count
associated with the peth3 adapter (there seem to be 1.5 million
interrupt requests per hour, and this system is only being accessed by
one or two other hosts, with no network intensive activities).

I'd really appreciate any help you can provide to diagnose and solve
this problem.


Thanks in advance,
Alex


--------------------------------------
System configuration details
--------------------------------------

cat /proc/version

Linux version 2.6.18-6-xen-amd64 (Debian 2.6.18.dfsg.1-18etch1)
(waldi@xxxxxxxxxx) (gcc version 4.1.2 20061115 (prerelease) (Debian
4.1.1-21)) #1 SMP Sun Feb 10 18:02:52 UTC 2008

dpkg -l | grep xen

ii  linux-headers-2.6.18-6-xen          2.6.18.dfsg.1-18etch1
      Common header files for Linux 2.6.18
ii  linux-headers-2.6.18-6-xen-amd64    2.6.18.dfsg.1-18etch1
      Header files for Linux 2.6.18 on AMD64
ii  linux-image-2.6.18-6-xen-amd64      2.6.18.dfsg.1-18etch1
      Linux 2.6.18 image on AMD64
ii  linux-modules-2.6.18-6-xen-amd64    2.6.18.dfsg.1-18etch1
      Linux 2.6.18 modules on AMD64
ii  xen-hypervisor-3.0.3-1-amd64        3.0.3-0-4
      The Xen Hypervisor on AMD64
ii  xen-linux-system-2.6.18-6-xen-amd64 2.6.18.dfsg.1-18etch1
      XEN system with Linux 2.6.18 image on AMD64
ii  xen-tools                           2.8-2
      Tools to manage debian XEN virtual servers
ii  xen-utils-3.0.3-1                   3.0.3-0-4
      XEN administrative tools
ii  xen-utils-common                    3.0.3-0-2
      XEN administrative tools - common files

lspci | grep -i eth

01:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd.
RTL8111/8168B PCI Express Gigabit Ethernet controller (rev 01) [1]
02:09.0 Ethernet controller: Realtek Semiconductor Co., Ltd.
RTL-8139/8139C/8139C+ (rev 10) [2]
02:0a.0 Ethernet controller: Realtek Semiconductor Co., Ltd.
RTL-8139/8139C/8139C+ (rev 10) [3]

[1] This is the adapter attached to the local network, shown in Dom0 as eth3
[2] This adapter handles a broadband connection
[3] This one is hidden from Dom0 (reserved for DomU)

cat /proc/cpuinfo

processor       : 0
vendor_id       : AuthenticAMD
cpu family      : 15
model           : 107
model name      : AMD Athlon(tm) 64 X2 Dual Core Processor 4200+
stepping        : 2
cpu MHz         : 2365.072
cache size      : 512 KB
physical id     : 0
siblings        : 1
core id         : 0
cpu cores       : 1
fpu             : yes
fpu_exception   : yes
cpuid level     : 1
wp              : yes
flags           : fpu tsc msr pae mce cx8 apic mtrr mca cmov pat pse36
clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt rdtscp lm
3dnowext 3dnow pni cx16 lahf_lm cmp_legacy svm cr8_legacy
bogomips        : 5913.87
TLB size        : 1024 4K pages
clflush size    : 64
cache_alignment : 64
address sizes   : 40 bits physical, 48 bits virtual
power management: ts fid vid ttp tm stc [6]

processor       : 1
vendor_id       : AuthenticAMD
cpu family      : 15
model           : 107
model name      : AMD Athlon(tm) 64 X2 Dual Core Processor 4200+
stepping        : 2
cpu MHz         : 2365.072
cache size      : 512 KB
physical id     : 1
siblings        : 1
core id         : 0
cpu cores       : 1
fpu             : yes
fpu_exception   : yes
cpuid level     : 1
wp              : yes
flags           : fpu tsc msr pae mce cx8 apic mtrr mca cmov pat pse36
clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt rdtscp lm
3dnowext 3dnow pni cx16 lahf_lm cmp_legacy svm cr8_legacy
bogomips        : 5913.87
TLB size        : 1024 4K pages
clflush size    : 64
cache_alignment : 64
address sizes   : 40 bits physical, 48 bits virtual
power management: ts fid vid ttp tm stc [6]

cat /proc/interrupts | grep eth

           CPU0              CPU1
 18:    6302230          0        Phys-irq  peth3
 21:        826          0        Phys-irq  eth1

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