[Xen-users] Very large latency during network activity

[Pepe Barbe <elventear@xxxxxxxxx>]

Hello,

I am running Xen 3.3.1 with a Centos 5.3 dom0 and with 3 Ubuntu 8.04  
and 1 Centos 5.3 dom0. One of the Ubuntu dom0s has two interfaces, one  
real PCI assigned via passthrough and one virtual; this host works as  
the router for the Network it serves.
The problem that I have is that when network traffic picks up, and by  
this I mean rates close to 1Mbps, the network latency starts to creep  
up. From an average of a 100ms, it goes up to 3s, with spiks up to  
10s. This is unbearable given that is a fair amount of interactive  
usage in the network.
What can I do to figure out what is the issue here, and if there is a  
way to mitigate this problem? I have already limited the rate of the  
vifs to 5Mbps and I have QoS on the router limiting the outgoing  
speeds considerably below the max and prioritizing small packets to  
improve interactive sessions.
I've checked the load of the entire system using xentop and the  
overall CPU usage does not go above 10%, nor the virtual machines are  
memory starved.
I don't know if this is related, but I get the following error in my  
kernel log:
irq 21: nobody cared (try booting with the "irqpoll" option)

Call Trace:
 <IRQ>  [<ffffffff802b1483>] __report_bad_irq+0x30/0x7d
 [<ffffffff802b16ba>] note_interrupt+0x1ea/0x22b
 [<ffffffff802b0bb2>] __do_IRQ+0xbd/0x103
 [<ffffffff8028e122>] _local_bh_enable+0x61/0xc5
 [<ffffffff8026cf04>] do_IRQ+0xe7/0xf5
 [<ffffffff803a6cca>] evtchn_do_upcall+0x13b/0x1fb
 [<ffffffff8025f8d6>] do_hypervisor_callback+0x1e/0x2c
 <EOI>  [<ffffffff8026df02>] monotonic_clock+0x35/0x7b
 [<ffffffff802063aa>] hypercall_page+0x3aa/0x1000
 [<ffffffff802063aa>] hypercall_page+0x3aa/0x1000
 [<ffffffff8026e4e5>] raw_safe_halt+0x84/0xa8
 [<ffffffff8026ba22>] xen_idle+0x38/0x4a
 [<ffffffff8024a803>] cpu_idle+0x97/0xba
 [<ffffffff80634b09>] start_kernel+0x21f/0x224
 [<ffffffff806341e5>] _sinittext+0x1e5/0x1eb

handlers:
[<ffffffff803dab93>] (usb_hcd_irq+0x0/0x55)
Disabling IRQ #21

I've already passed the irq=poll parameter to the kernel, but I keep  
getting this error. Is it related?
Thanks,
Pepe

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