Re: [Xen-devel] [RFC] Add static priority into credit scheduler

[NISHIGUCHI Naoki <nisiguti@xxxxxxxxxxxxxx>]

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


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