Re: Offline state in scheduling

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

On 29/06/10 12:42, Yuyang Du wrote:
> Is it right to say the time HVM waits for I/O equals the offline time (given no administrator pauses)?

There are some I/O events that are handled inside of Xen (such as APIC 
accesses); these don't cause a vcpu to be paused.  I think in the normal 
course of operation, an HVM vcpu is only paused when doing I/O.  Other 
reasons might be administrator pause, migration, save/restore, domain 
creation, memory sharing / page swapping, and so on.  But if you aren't 
doing any of those, I think I/O done in QEMU would be the only reason.

> I am testing apache web server in a HVM, and I find that vcpu blocking state makes up a large portion. Since the HVM can not issue SCHED_block hypercalls, so the blocking state means the VM is not cpu intensive and often executes HLT to halt itself?

Yes.  If you take a trace to include VMX / SVM events, and use xenalyze, 
you should be able to see the HLT vmexit before blocking.

  -George