Bug 524976

Description of problem:
When the total number of vcpu's on a host is larger than the number of physical processors, there is the possibility that a vcpu on a multi cpu guest will be preempted by the hypervisor while the vcpu holds a kernel lock.  Then other vcpu's on the guest that are trying to acquire the lock simply spin.

The customer is currently adjusting the real time priority and using the nice command to shorten the time slice of the qemu on the host. They feel this does help improve performance in these situations. They have asked us to include something like this part of an official maintenance release of RHEL 5.

They are wanting it addressed in RHEL 5 because “over-provisioning is one of the features users like to exploit on virtualization.”  I have discussed this briefly with Chris Wright and he agreed a BZ should be opened to address this.