Re: [RFC] Add static priority into credit scheduler

[NISHIGUCHI Naoki <nisiguti@jp.fujitsu.com>]

Su, Disheng wrote:
> NISHIGUCHI Naoki wrote:
>> I understand what you mean.
>> I doubt whether the rest of cpu not used by RT guest is reflected to
>> credit of non-RT guests. If RT guest might monopolize the whole cpu, I
>> think the rest of cpu is nothing, therefore non-RT guests have no
>> credit. 
>>
> 
> Yes, it's an issue need to be addressed for client virtualization case, due to the primary guest(e,g Windows) is not a trusted guest.
> When detecting one RT guest is monopolize cpu for a while(e.g. 1-2minute), one can:
> 1. kill the RT guest...
> 2. lower its priority for a while, give other guests the opportunity to run, then restore its previous priority
> Any ideas? 

What I mean is credit_total given to non-RT guest in scheduler.
If a PC has 4 core cpu and an RT guest has 4 vcpu, I think credit_total 
would be 0, because we could not predict behavior of the RT guest .

> Oh, forgot to mention you need to pin the RT guest, or try the attached patch.
> If you set one guest as high priority, it increases the chance that its vcpus are migrated back and forth, because the priority is fixed and higher than  
> OVER.

I tried your patch. The result was the same.
I also pin the RT guest and dom0 as follows, but HVM did not work well.
             vcpu cpu
      dom0     0   0
               1   1
               2   2
               3   3
      HVM      0   0
               1   1
               2   2
               3   3

It seems to me that idle cpus are not effectively used.

> Don't migrate the RT guest in practice. It's the same with Bcredit from my previous experience, isn't it?

I think that scheduler should not migrate the vcpu needlessly, but 
necessary migration should be done.

Best regards,
Naoki Nishiguchi