Re: [Xen-devel] RE: The caculation of the credit in credit_scheduler

[Juergen Gross <juergen.gross@xxxxxxxxxxxxxx>]

On 11/10/10 03:39, Jiang, Yunhong wrote:
> > -----Original Message-----
> > From: George Dunlap [mailto:George.Dunlap@xxxxxxxxxxxxx]
> > Sent: Tuesday, November 09, 2010 10:27 PM
> > To: Jiang, Yunhong
> > Cc: xen-devel@xxxxxxxxxxxxxxxxxxx; Dong, Eddie; Zhang, Xiantao
> > Subject: Re: The caculation of the credit in credit_scheduler
> >
> > On 05/11/10 07:06, Jiang, Yunhong wrote:
> > > The reason is how the credit is caculated. Although the 3 HVM domains is pinned
> > to 2 PCPU and share the 2 CPUs, they will all get 2* 300 credit when credit 
> > account.
> > That means the I/O intensive HVM domain will never be under credit, thus it will
> > preempt the CPU intensive whenever it is boost (i.e. after I/O access to QEMU), 
> > and
> > it is set to be TS_UNDER only at the tick time, and then, boost again.
> >
> > I suspect that the real reason you're having trouble is that pinning and
> > the credit mechanism don't work very well together.  Instead of pinning,
> > have you tried using the cpupools interface to make a 2-cpu pool to put
> > the VMs into?  That should allow the credit to be divided appropriately.
> I have a quick look in the code, and seems the cpu pool should not help on such 
> situation. The CPU poll only cares about the CPUs a domain can be scheduled, 
> but not about the credit caculation.
With cpupools you avoid the pinning. This will result in better credit
calculation results.


Juergen

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Juergen Gross                 Principal Developer Operating Systems
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