Re: [Xen-devel] Strange interdependace between domains

[Don Slutz <dslutz@xxxxxxxxxxx>]

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,
> Dario

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