On 09/21/2012 08:00 AM, Raghavendra K T wrote:
From: Raghavendra K T <raghavendra...@linux.vnet.ibm.com>
When total number of VCPUs of system is less than or equal to physical CPUs,
PLE exits become costly since each VCPU can have dedicated PCPU, and
trying to find a target VCPU to yield_to just burns time in PLE handler.
This patch reduces overhead, by simply doing a return in such scenarios by
checking the length of current cpu runqueue.
I am not convinced this is the way to go.
The VCPU that is holding the lock, and is not releasing it,
probably got scheduled out. That implies that VCPU is on a
runqueue with at least one other task.
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1629,6 +1629,9 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me)
int pass;
int i;
+ if (unlikely(rq_nr_running() == 1))
+ return;
+
kvm_vcpu_set_in_spin_loop(me, true);
/*
* We boost the priority of a VCPU that is runnable but not
--
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