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. Is this enough for a CPU with HT that has a busy sibling thread, or should it be even larger? On the X5670, loading up the sibling thread with an infinite loop does not seem to increase the required ple_gap. Signed-off-by: Rik van Riel <riel@xxxxxxxxxx> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index 81fcbe9..c61fcbf 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -90,14 +90,14 @@ module_param(vmm_exclusive, 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); -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
