KVM: PPC: Decrease the powerpc default halt poll max value

KVM_HALT_POLL_NS_DEFAULT is an arch specific constant which sets the
default value of the halt_poll_ns kvm module parameter which determines
the global maximum halt polling interval.

The current value for powerpc is 500000 (500us) which means that any
repetitive workload with a period of less than that can drive the cpu
usage to 100% where it may have been mostly idle without halt polling.
This presents the possibility of a large increase in power usage with
a comparatively small performance benefit.

Reduce the default to 10000 (10us) and a user can tune this themselves
to set their affinity for halt polling based on the trade off between power
and performance which they are willing to make.
Signed-off-by: Suraj Jitindar Singh <sjitindarsingh@gmail.com>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

arch/powerpc/include/asm/kvm_host.h

@@ -48,7 +48,7 @@
 #ifdef CONFIG_KVM_MMIO
 #define KVM_COALESCED_MMIO_PAGE_OFFSET 1
 #endif
-#define KVM_HALT_POLL_NS_DEFAULT 500000
+#define KVM_HALT_POLL_NS_DEFAULT 10000	/* 10 us */
 
 /* These values are internal and can be increased later */
 #define KVM_NR_IRQCHIPS          1