Commit 00c25bce authored Jan 04, 2011 by Rik van Riel Committed by Marcelo Tosatti Mar 17, 2011

KVM: VMX: increase ple_gap default to 128

On some CPUs, a ple_gap of 41 is simply insufficient to ever trigger
PLE exits, even with the minimalistic PLE test from kvm-unit-tests.

http://git.kernel.org/?p=virt/kvm/kvm-unit-tests.git;a=commitdiff;h=eda71b28fa122203e316483b35f37aaacd42f545



For example, the Xeon X5670 CPU needs a ple_gap of at least 48 in
order to get pause loop exits:

# modprobe kvm_intel ple_gap=47
# taskset 1 /usr/local/bin/qemu-system-x86_64 \
  -device testdev,chardev=log -chardev stdio,id=log \
  -kernel x86/vmexit.flat -append ple-round-robin -smp 2
VNC server running on `::1:5900'
enabling apic
enabling apic
ple-round-robin 58298446
# rmmod kvm_intel
# modprobe kvm_intel ple_gap=48
# taskset 1 /usr/local/bin/qemu-system-x86_64 \
   -device testdev,chardev=log -chardev stdio,id=log \
   -kernel x86/vmexit.flat -append ple-round-robin -smp 2
VNC server running on `::1:5900'
enabling apic
enabling apic
ple-round-robin 36616

Increase the ple_gap to 128 to be on the safe side.

Signed-off-by: Rik van Riel <riel@redhat.com>
Acked-by: Zhai, Edwin <edwin.zhai@intel.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

parent 3781c01c

arch/x86/kvm/vmx.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -93,14 +93,14 @@ module_param(yield_on_hlt, bool, S_IRUGO);
		* These 2 parameters are used to config the controls for Pause-Loop Exiting:
		* ple_gap: upper bound on the amount of time between two successive
		* executions of PAUSE in a loop. Also indicate if ple enabled.
		* According to test, this time is usually small than 41 cycles.
		* According to test, this time is usually smaller than 128 cycles.
		* ple_window: upper bound on the amount of time a guest is allowed to execute
		* in a PAUSE loop. Tests indicate that most spinlocks are held for
		* less than 2^12 cycles
		* Time is measured based on a counter that runs at the same rate as the TSC,
		* refer SDM volume 3b section 21.6.13 & 22.1.3.
		*/
		#define KVM_VMX_DEFAULT_PLE_GAP 41
		#define KVM_VMX_DEFAULT_PLE_GAP 128
		#define KVM_VMX_DEFAULT_PLE_WINDOW 4096
		static int ple_gap = KVM_VMX_DEFAULT_PLE_GAP;
		module_param(ple_gap, int, S_IRUGO);

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