Zhai, Edwin 4b8d54f972 KVM: VMX: Add support for Pause-Loop Exiting ... New NHM processors will support Pause-Loop Exiting by adding 2 VM-execution control fields: PLE_Gap - upper bound on the amount of time between two successive executions of PAUSE in a loop. PLE_Window - upper bound on the amount of time a guest is allowed to execute in a PAUSE loop If the time, between this execution of PAUSE and previous one, exceeds the PLE_Gap, processor consider this PAUSE belongs to a new loop. Otherwise, processor determins the the total execution time of this loop(since 1st PAUSE in this loop), and triggers a VM exit if total time exceeds the PLE_Window. * Refer SDM volume 3b section 21.6.13 & 22.1.3. Pause-Loop Exiting can be used to detect Lock-Holder Preemption, where one VP is sched-out after hold a spinlock, then other VPs for same lock are sched-in to waste the CPU time. Our tests indicate that most spinlocks are held for less than 212 cycles. Performance tests show that with 2X LP over-commitment we can get +2% perf improvement for kernel build(Even more perf gain with more LPs). Signed-off-by: Zhai Edwin <edwin.zhai@intel.com> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>		2009-12-03 09:32:17 +02:00
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asm	KVM: VMX: Add support for Pause-Loop Exiting	2009-12-03 09:32:17 +02:00