From: Wanpeng Li <wanpengli@xxxxxxxxxxx>
Waiman Long mentioned that:
Generally speaking, unfair lock performs well for VMs with a small
number of vCPUs. Native qspinlock may perform better than pvqspinlock
if there is vCPU pinning and there is no vCPU over-commitment.
This patch adds a performance hint to allow hypervisor admin to choose
the qspinlock to be used when a dedicated pCPU is available.
PV_DEDICATED = 1, PV_UNHALT = anything: default is qspinlock
PV_DEDICATED = 0, PV_UNHALT = 1: default is Hybrid PV queued/unfair lock
PV_DEDICATED = 0, PV_UNHALT = 0: default is tas
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx>
Signed-off-by: Wanpeng Li <wanpengli@xxxxxxxxxxx>
---
Documentation/virtual/kvm/cpuid.txt | 6 ++++++
arch/x86/include/uapi/asm/kvm_para.h | 1 +
arch/x86/kernel/kvm.c | 6 ++++++
3 files changed, 13 insertions(+)
diff --git a/Documentation/virtual/kvm/cpuid.txt b/Documentation/virtual/kvm/cpuid.txt
index 87a7506..c0740b1 100644
--- a/Documentation/virtual/kvm/cpuid.txt
+++ b/Documentation/virtual/kvm/cpuid.txt
@@ -54,6 +54,12 @@ KVM_FEATURE_PV_UNHALT || 7 || guest checks this feature bit
|| || before enabling paravirtualized
|| || spinlock support.
------------------------------------------------------------------------------
+KVM_FEATURE_PV_DEDICATED || 8 || guest checks this feature bit
+ || || to determine if they run on
+ || || dedicated vCPUs, allowing opti-
+ || || mizations such as usage of
+ || || qspinlocks.
+------------------------------------------------------------------------------
KVM_FEATURE_PV_TLB_FLUSH || 9 || guest checks this feature bit
|| || before enabling paravirtualized
|| || tlb flush.
diff --git a/arch/x86/include/uapi/asm/kvm_para.h b/arch/x86/include/uapi/asm/kvm_para.h
index 6cfa9c8..9a5ef67 100644
--- a/arch/x86/include/uapi/asm/kvm_para.h
+++ b/arch/x86/include/uapi/asm/kvm_para.h
@@ -25,6 +25,7 @@
#define KVM_FEATURE_STEAL_TIME 5
#define KVM_FEATURE_PV_EOI 6
#define KVM_FEATURE_PV_UNHALT 7
+#define KVM_FEATURE_PV_DEDICATED 8
#define KVM_FEATURE_PV_TLB_FLUSH 9
#define KVM_FEATURE_ASYNC_PF_VMEXIT 10
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index aa2b706..6f0e43f 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -726,6 +726,12 @@ void __init kvm_spinlock_init(void)
{
if (!kvm_para_available())
return;
+
+ if (kvm_para_has_feature(KVM_FEATURE_PV_DEDICATED)) {
+ static_branch_disable(&virt_spin_lock_key);
+ return;
+ }
+
/* Does host kernel support KVM_FEATURE_PV_UNHALT? */
if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT))
return;
--
2.7.4
