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authorZhai, Edwin <edwin.zhai@intel.com>2009-10-09 18:03:20 +0800
committerAvi Kivity <avi@redhat.com>2009-12-03 09:32:17 +0200
commit4b8d54f9726f1159330201c5ed2ea30bce7e63ea (patch)
tree903eaf21f46359f3e42a6d4582ca792b73d4b7b9 /arch/x86/kvm
parentd255f4f2bac81eb798fcf76938147f1f6c756ae2 (diff)
KVM: VMX: Add support for Pause-Loop Exiting
New NHM processors will support Pause-Loop Exiting by adding 2 VM-execution control fields: PLE_Gap - upper bound on the amount of time between two successive executions of PAUSE in a loop. PLE_Window - upper bound on the amount of time a guest is allowed to execute in a PAUSE loop If the time, between this execution of PAUSE and previous one, exceeds the PLE_Gap, processor consider this PAUSE belongs to a new loop. Otherwise, processor determins the the total execution time of this loop(since 1st PAUSE in this loop), and triggers a VM exit if total time exceeds the PLE_Window. * Refer SDM volume 3b section 21.6.13 & 22.1.3. Pause-Loop Exiting can be used to detect Lock-Holder Preemption, where one VP is sched-out after hold a spinlock, then other VPs for same lock are sched-in to waste the CPU time. Our tests indicate that most spinlocks are held for less than 212 cycles. Performance tests show that with 2X LP over-commitment we can get +2% perf improvement for kernel build(Even more perf gain with more LPs). Signed-off-by: Zhai Edwin <edwin.zhai@intel.com> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Diffstat (limited to 'arch/x86/kvm')
-rw-r--r--arch/x86/kvm/vmx.c51
1 files changed, 50 insertions, 1 deletions
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 70020e505c22..a4580d65af59 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -61,6 +61,25 @@ module_param_named(unrestricted_guest,
static int __read_mostly emulate_invalid_guest_state = 0;
module_param(emulate_invalid_guest_state, 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.
+ * 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_WINDOW 4096
+static int ple_gap = KVM_VMX_DEFAULT_PLE_GAP;
+module_param(ple_gap, int, S_IRUGO);
+
+static int ple_window = KVM_VMX_DEFAULT_PLE_WINDOW;
+module_param(ple_window, int, S_IRUGO);
+
struct vmcs {
u32 revision_id;
u32 abort;
@@ -319,6 +338,12 @@ static inline int cpu_has_vmx_unrestricted_guest(void)
SECONDARY_EXEC_UNRESTRICTED_GUEST;
}
+static inline int cpu_has_vmx_ple(void)
+{
+ return vmcs_config.cpu_based_2nd_exec_ctrl &
+ SECONDARY_EXEC_PAUSE_LOOP_EXITING;
+}
+
static inline int vm_need_virtualize_apic_accesses(struct kvm *kvm)
{
return flexpriority_enabled &&
@@ -1240,7 +1265,8 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf)
SECONDARY_EXEC_WBINVD_EXITING |
SECONDARY_EXEC_ENABLE_VPID |
SECONDARY_EXEC_ENABLE_EPT |
- SECONDARY_EXEC_UNRESTRICTED_GUEST;
+ SECONDARY_EXEC_UNRESTRICTED_GUEST |
+ SECONDARY_EXEC_PAUSE_LOOP_EXITING;
if (adjust_vmx_controls(min2, opt2,
MSR_IA32_VMX_PROCBASED_CTLS2,
&_cpu_based_2nd_exec_control) < 0)
@@ -1386,6 +1412,9 @@ static __init int hardware_setup(void)
if (enable_ept && !cpu_has_vmx_ept_2m_page())
kvm_disable_largepages();
+ if (!cpu_has_vmx_ple())
+ ple_gap = 0;
+
return alloc_kvm_area();
}
@@ -2298,9 +2327,16 @@ static int vmx_vcpu_setup(struct vcpu_vmx *vmx)
exec_control &= ~SECONDARY_EXEC_ENABLE_EPT;
if (!enable_unrestricted_guest)
exec_control &= ~SECONDARY_EXEC_UNRESTRICTED_GUEST;
+ if (!ple_gap)
+ exec_control &= ~SECONDARY_EXEC_PAUSE_LOOP_EXITING;
vmcs_write32(SECONDARY_VM_EXEC_CONTROL, exec_control);
}
+ if (ple_gap) {
+ vmcs_write32(PLE_GAP, ple_gap);
+ vmcs_write32(PLE_WINDOW, ple_window);
+ }
+
vmcs_write32(PAGE_FAULT_ERROR_CODE_MASK, !!bypass_guest_pf);
vmcs_write32(PAGE_FAULT_ERROR_CODE_MATCH, !!bypass_guest_pf);
vmcs_write32(CR3_TARGET_COUNT, 0); /* 22.2.1 */
@@ -3348,6 +3384,18 @@ out:
}
/*
+ * Indicate a busy-waiting vcpu in spinlock. We do not enable the PAUSE
+ * exiting, so only get here on cpu with PAUSE-Loop-Exiting.
+ */
+static int handle_pause(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
+{
+ skip_emulated_instruction(vcpu);
+ kvm_vcpu_on_spin(vcpu);
+
+ return 1;
+}
+
+/*
* The exit handlers return 1 if the exit was handled fully and guest execution
* may resume. Otherwise they set the kvm_run parameter to indicate what needs
* to be done to userspace and return 0.
@@ -3383,6 +3431,7 @@ static int (*kvm_vmx_exit_handlers[])(struct kvm_vcpu *vcpu) = {
[EXIT_REASON_MCE_DURING_VMENTRY] = handle_machine_check,
[EXIT_REASON_EPT_VIOLATION] = handle_ept_violation,
[EXIT_REASON_EPT_MISCONFIG] = handle_ept_misconfig,
+ [EXIT_REASON_PAUSE_INSTRUCTION] = handle_pause,
};
static const int kvm_vmx_max_exit_handlers =