Github user jharshman commented on the pull request:
https://github.com/apache/cloudstack/pull/1013#issuecomment-152675128
My apologies Daan,
I am happy to clarify.
The PR for this Jira ticket (9004), was created as a subtask of
CLOUDSTACK-8978. It's intent is to add the ability to set certain hv
parameters with an end goal in 8978 of implementing hyper-V enlightenment
features for Windows Server 2008 guests.
The current code for HyperVEnlightenmentFeatureDef only allowed the setting
of the hv_relaxed bit. This bit disables a windows sanity check that commonly
results in a BSOD when the VM is running on a host under heavy load.
The change here adds the ability to set the hv_vapic and hv_spinlocks bits
as well as retry time. The hv_vapic bit tries to reduce interrupt overhead in
guests. The hv_spinlock bit is used by the guest to notify the hypervisor that
the calling virtual processor is attempting to access a resource that may be
held by another virtual processor. For the host, the retry value for
hv_spinlock indicates the number of times the virtual processor should attempt
to access before the spinlock is considered excessive.
Basically these changes are setting the stage for changes I am going to
submit in CLOUDSTACK-8974.
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