Re: [KVM PATCH 2/2] KVM: PPC: Book3S HV: Report stolen time to guest through dispatch trace log

[Alexander Graf <agraf@suse.de>]

On 20.12.2011, at 11:37, Paul Mackerras wrote:

> This adds code to measure "stolen" time per virtual core in units of
> timebase ticks, and to report the stolen time to the guest using the
> dispatch trace log (DTL).  The guest can register an area of memory
> for the DTL for a given vcpu.  The DTL is a ring buffer where KVM
> fills in one entry every time it enters the guest for that vcpu.
> 
> Stolen time is measured as time when the virtual core is not running,
> either because the vcore is not runnable (e.g. some of its vcpus are
> executing elsewhere in the kernel or in userspace), or when the vcpu
> thread that is running the vcore is preempted.  This includes time
> when all the vcpus are idle (i.e. have executed the H_CEDE hypercall),
> which is OK because the guest accounts stolen time while idle as idle
> time.
> 
> Each vcpu keeps a record of how much stolen time has been reported to
> the guest for that vcpu so far.  When we are about to enter the guest,
> we create a new DTL entry (if the guest vcpu has a DTL) and report the
> difference between total stolen time for the vcore and stolen time
> reported so far for the vcpu as the "enqueue to dispatch" time in the
> DTL entry.
> 
> Signed-off-by: Paul Mackerras <paulus@samba.org>

This patch makes sense and looks good to me :)


Alex