Strange interdependace between domains

[Simon Martin <furryfuttock@gmail.com>]

Hi all,

Sorry, I just sent this without a subject. Here it is with the subject
as it should be.

I  am  now successfully running my little operating system inside Xen.
It  is  fully  preemptive and working a treat, but I have just noticed
something  I  wasn't expecting, and will really be a problem for me if
I can't work around it.

My configuration is as follows:

1.- Hardware: Intel i3, 4GB RAM, 64GB SSD.

2.- Xen: 4.4 (just pulled from repository)

3.- Dom0: Debian Wheezy (Kernel 3.2)

4.- 2 cpu pools:

# xl cpupool-list
Name               CPUs   Sched     Active   Domain count
Pool-0               3    credit       y          2
pv499                1  arinc653       y          1

5.- 2 domU:

# xl list
Name                                        ID   Mem VCPUs      State   Time(s)
Domain-0                                     0   984     3     r-----      39.7
win7x64                                      1  2046     3     -b----     143.0
pv499                                        3   128     1     -b----      61.2

6.- All VCPUs are pinned:

# xl vcpu-list
Name                                ID  VCPU   CPU State   Time(s) CPU Affinity
Domain-0                             0     0    0   -b-      27.5  0
Domain-0                             0     1    1   -b-       7.2  1
Domain-0                             0     2    2   r--       5.1  2
win7x64                              1     0    0   -b-      71.6  0
win7x64                              1     1    1   -b-      37.7  1
win7x64                              1     2    2   -b-      34.5  2
pv499                                3     0    3   -b-      62.1  3

7.- pv499 is the domU that I am testing. It has no disk or vif devices
(yet). I am running a little test program in pv499 and the timing I
see is varies depending on disk activity.

My test program runs prints up the time taken in milliseconds for a
million cycles. With no disk activity I see 940 ms, with disk activity
I see 1200 ms.

I can't understand this as disk activity should be running on cores 0,
1  and 2, but never on core 3. The only thing running on core 3 should
by my paravirtual machine and the hypervisor stub.

Any idea what's going on?


-- 
Best regards,
 Simon                          mailto:furryfuttock@gmail.com