Re: [Xen-devel] Strange interdependace between domains

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

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. :-)

> 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
> pv499              3
> 
> 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

-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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