Re: Question about the ability of credit scheduler to handle I/O and CPU intensive VMs

[George Dunlap <George.Dunlap@eu.citrix.com>]

On Tue, Oct 5, 2010 at 3:52 AM, Yuehai Xu <yuehaixu@gmail.com> wrote:
> However, I stop one of the CPU intensive program in a DomU while keep
> the other running, the results are:
> .....
> <  0.327815345 |x d1v0> (dom: 1) --> (dom: 2) vruntime : 1542607)
> <  0.327906620 -x d2v0> (dom: 2) --> (dom: 1) vruntime : 109521)
> <  0.344349033 |x d1v0> (dom: 1) --> (dom: 2) vruntime : 19779544)
> <  0.344377129 -x d2v0> (dom: 2) --> (dom: 1) vruntime : 33528)
> <  0.344570662 |x d1v0> (dom: 1) --> (dom: 2) vruntime : 232540)
> <  0.344643933 -x d2v0> (dom: 2) --> (dom: 1) vruntime : 87857)
> <  0.345009170 |x d1v0> (dom: 1) --> (dom: 2) vruntime : 439081)
> <  0.345034387 -x d2v0> (dom: 2) --> (dom: 1) vruntime : 30059)
> <  0.369973183 -x d1v0> (dom: 1) --> (dom: 1) vruntime : 30000506)
> <  0.392423279 |x d1v0> (dom: 1) --> (dom: 2) vruntime : 27006658)
> ....
>
> Here I am gotten confusing, since my algorithm of scheduling is very
> simple, every VM should have 30ms of PCPU, however, from the results,
> the time for
> each VCPU to have PCPU is quite unstable. I think somewhere, the
> routine of schedule() should be invoked frequently, and from xentop,
> the VM with CPU
> intensive occupies PCPU almost at 97%.

Idle VMs are never 100% idle; there are a lot of "maintenance" tasks
still to be done.

Your mostly-idle domain (domain 2) seems to be running for pretty
short periods of time -- less than 100us.  That's pretty reasonable.

The question to ask is, what happens when domain 2 wakes up -- is it
put on the runqueue, waiting for the running domain to finish its
timeslice?  Or is it run immediately?  Given the trace you give here,
I would guess that it's run immediately.  If that's not what you
expect, you need to figure out why it's doing that and make it do
something else. :-)

 -George