If guest kernel is configured with nopvspin, or guest find its has
dedicated pCPUs from realtime hint feature, the pvspinlock will be
disabled, and vCPU preemption check is disabled too.
but KVM still can emulating HLT for vCPU for both cases, and check
if vCPU is preempted or not, and can boost performance
Like unixbench, single copy, guest kernel with nopvspin:
Testcase Base with patch
System Benchmarks Index Values INDEX INDEX
Dhrystone 2 using register variables 3278.4 3277.7
Double-Precision Whetstone 822.8 825.8
Execl Throughput 1296.5 941.1
File Copy 1024 bufsize 2000 maxblocks 2124.2 2142.7
File Copy 256 bufsize 500 maxblocks 1335.9 1353.6
File Copy 4096 bufsize 8000 maxblocks 4256.3 4760.3
Pipe Throughput 1050.1 1054.0
Pipe-based Context Switching 243.3 352.0
Process Creation 820.1 814.4
Shell Scripts (1 concurrent) 2169.0 2086.0
Shell Scripts (8 concurrent) 7710.3 7576.3
System Call Overhead 672.4 673.9
======== =======
System Benchmarks Index Score 1467.2 1483.0
Co-developed-by: Wang GuangJu <wangguangju@xxxxxxxxx>
Signed-off-by: Wang GuangJu <wangguangju@xxxxxxxxx>
Signed-off-by: Li RongQing <lirongqing@xxxxxxxxx>
---
diff v1: move the vcpu_is_preempted setting into kvm_guest_init,
to reduce a check of kvm_para_has_feature(KVM_FEATURE_STEAL_TIME)
arch/x86/kernel/kvm.c | 7 +++----
1 file changed, 3 insertions(+), 4 deletions(-)
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index d77481ec..3da39da 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -764,6 +764,9 @@ static void __init kvm_guest_init(void)
if (kvm_para_has_feature(KVM_FEATURE_STEAL_TIME)) {
has_steal_clock = 1;
static_call_update(pv_steal_clock, kvm_steal_clock);
+
+ pv_ops.lock.vcpu_is_preempted =
+ PV_CALLEE_SAVE(__kvm_vcpu_is_preempted);
}
if (kvm_para_has_feature(KVM_FEATURE_PV_EOI))
@@ -1081,10 +1084,6 @@ void __init kvm_spinlock_init(void)
pv_ops.lock.wait = kvm_wait;
pv_ops.lock.kick = kvm_kick_cpu;
- if (kvm_para_has_feature(KVM_FEATURE_STEAL_TIME)) {
- pv_ops.lock.vcpu_is_preempted =
- PV_CALLEE_SAVE(__kvm_vcpu_is_preempted);
- }
/*
* When PV spinlock is enabled which is preferred over
* virt_spin_lock(), virt_spin_lock_key's value is meaningless.
--
2.9.4
