KVM: ppc: Implement in-kernel exit timing statistics

Existing KVM statistics are either just counters (kvm_stat) reported for
KVM generally or trace based aproaches like kvm_trace.
For KVM on powerpc we had the need to track the timings of the different exit
types. While this could be achieved parsing data created with a kvm_trace
extension this adds too much overhead (at least on embedded PowerPC) slowing
down the workloads we wanted to measure.

Therefore this patch adds a in-kernel exit timing statistic to the powerpc kvm
code. These statistic is available per vm&vcpu under the kvm debugfs directory.
As this statistic is low, but still some overhead it can be enabled via a
.config entry and should be off by default.

Since this patch touched all powerpc kvm_stat code anyway this code is now
merged and simplified together with the exit timing statistic code (still
working with exit timing disabled in .config).

Signed-off-by: Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>
Signed-off-by: Hollis Blanchard <hollisb@us.ibm.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

arch/powerpc/kvm/Kconfig

@@ -32,6 +32,17 @@ config KVM_440
 
 	  If unsure, say N.
 
+config KVM_EXIT_TIMING
+	bool "Detailed exit timing"
+	depends on KVM
+	---help---
+	  Calculate elapsed time for every exit/enter cycle. A per-vcpu
+	  report is available in debugfs kvm/vm#_vcpu#_timing.
+	  The overhead is relatively small, however it is not recommended for
+	  production environments.
+
+	  If unsure, say N.
+
 config KVM_TRACE
 	bool "KVM trace support"
 	depends on KVM && MARKERS && SYSFS