Re: Strange interdependace between domains

[Don Slutz <dslutz@verizon.com>]

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
>