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Re: [Xen-devel] Strange interdependace between domains

On 02/18/14 11:55, Dario Faggioli wrote:
On lun, 2014-02-17 at 12:46 +0000, Simon Martin wrote:
Hyperthreading is just a way to improve CPU resource utilization. Even
if you are doing a CPU intensive operation, a lot of the processor
circuits are actually idle, so adding 2 pipelines to feed one
processor is a good way to improve total throughput, but it does have
it have it's caveats. I totally forgot this.

Given the way that this works there isn't much that Xen can do. It is
a physical restriction.

I know, and my point was not that we should try to "fix" in Xen, what's
impossible to fix, because it's just how hardware works... and that is
by design!

I was only saying that there are cases, when you still need isolation,
but you can afford a bit more of uncertainty, there is the possibility
for Xen to at least try to do the right thing automagically.

Basically, I'm ok with people looking for hard real-time response time
and jitter to have to pick up the proper hw platform, as a first step,
and properly fine tune it. For more _soft_ real-time workloads, I wish
we were (think we should be) able to do better, perhaps still with some
user required tweaks, but nothing equally intrusive, that's it. :-)

I would thing that a warning message from the xl command(s) dealing with 
cpupool would help here.  See below

OK. This is my current configuration:

Dom0     PCPU 0,1,2   no pinning
win7x64  PCPU   1,2   pinned
pv499    PCPU       3 pinned

And I get the same interdependence.

root@smartin-xen:~# xl list
Name                                        ID   Mem VCPUs      State   Time(s)
Domain-0                                     0  1253     3     r-----      37.1
win7x64                                      4  2046     2     ------     106.8
pv499                                        5   128     1     r-----      66.8
root@smartin-xen:~# xl vcpu-list
Name                                ID  VCPU   CPU State   Time(s) CPU Affinity
Domain-0                             0     0    1   -b-      21.2  all
Domain-0                             0     1    2   r--       8.8  all
Domain-0                             0     2    0   -b-       8.2  all
win7x64                              4     0    1   -b-      59.8  1
win7x64                              4     1    2   -b-      49.0  2
pv499                                5     0    3   r--      70.2  3
root@smartin-xen:~# xl cpupool-list -c
Name               CPU list
Pool-0             0,1,2

Change to something like:

Pool-0             0,1,2 (and part of 3)

pv499              3

Or add:

Warning: cpupool's share hyperthreaded cpus.

   -Don Slutz

I have gone back to my working settings.

Ok, thanks a lot for trying. I was hoping for that tweak, although
developed for completely different reasons, to be helpful in this case,
but it appears it is not.

Probably, I wouldn't have pinned the two win7 vcpus either, but anyway,
I don't want to eat any more of your time... Glad you find a
configuration that is working out! :-)

Thanks again and Regards,

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