kvm,compute-offering: prevent CPU limiting completely (#636)

* kvm,compute-offering: prevent CPU limiting completely

Related apache/cloudstack#12637

Signed-off-by: Abhishek Kumar <abhishek.mrt22@gmail.com>

* Apply suggestion from @DaanHoogland

Co-authored-by: dahn <daan.hoogland@gmail.com>

---------

Signed-off-by: Abhishek Kumar <abhishek.mrt22@gmail.com>
Co-authored-by: Abhisar Sinha <63767682+abh1sar@users.noreply.github.com>
Co-authored-by: dahn <daan.hoogland@gmail.com>

Author: 3 people

source/adminguide/service_offerings.rst

@@ -249,6 +249,14 @@ To create a new compute offering:
    -  **CPU cap**: Whether to limit the level of CPU usage even if spare
       capacity is available.
 
+      .. note::
+         On KVM hypervisor, to allow CloudStack to relinquish CPU usage control
+         entirely, set this option to false and set CPU speed to zero. Note that Instances
+         with zero CPU speed offerings should not be co-hosted with Instances using
+         non-zero CPU speed offerings, as the CPU speed value is used as a relative
+         weight (share) in the ``cputune`` section of the domain XML, and mixing zero
+         and non-zero values would skew the weighting.
+
    -  **Volatile**: If checked, Instances created from this service offering
       will have their root disks reset upon reboot. This is useful for
       secure environments that need a fresh start on every boot and for