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Subject[PATCH 1/3] KVM: add spinlock-exiting optimize framework
Date
If the vcpu(me) exit due to request a usermode spinlock, then
the spinlock-holder may be preempted in usermode or kernmode.

But if the vcpu(me) is in kernmode, then the holder must be
preempted in kernmode, so we should choose a vcpu in kernmode
as the most eligible candidate.

For some architecture(e.g. arm/s390), spin/preempt_in_kernel()
are the same, but they are different for X86.

Signed-off-by: Longpeng(Mike) <longpeng2@huawei.com>
---
arch/mips/kvm/mips.c | 10 ++++++++++
arch/powerpc/kvm/powerpc.c | 10 ++++++++++
arch/s390/kvm/kvm-s390.c | 10 ++++++++++
arch/x86/kvm/x86.c | 10 ++++++++++
include/linux/kvm_host.h | 2 ++
virt/kvm/arm/arm.c | 10 ++++++++++
virt/kvm/kvm_main.c | 4 ++++
7 files changed, 56 insertions(+)

diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c
index d4b2ad1..e04e6b3 100644
--- a/arch/mips/kvm/mips.c
+++ b/arch/mips/kvm/mips.c
@@ -98,6 +98,16 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu)
return !!(vcpu->arch.pending_exceptions);
}

+bool kvm_arch_vcpu_spin_in_kernel(struct kvm_vcpu *vcpu)
+{
+ return false;
+}
+
+bool kvm_arch_vcpu_preempt_in_kernel(struct kvm_vcpu *vcpu)
+{
+ return false;
+}
+
int kvm_arch_vcpu_should_kick(struct kvm_vcpu *vcpu)
{
return 1;
diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
index 1a75c0b..c573ddd 100644
--- a/arch/powerpc/kvm/powerpc.c
+++ b/arch/powerpc/kvm/powerpc.c
@@ -58,6 +58,16 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *v)
return !!(v->arch.pending_exceptions) || kvm_request_pending(v);
}

+bool kvm_arch_vcpu_spin_in_kernel(struct kvm_vcpu *vcpu)
+{
+ return false;
+}
+
+bool kvm_arch_vcpu_preempt_in_kernel(struct kvm_vcpu *vcpu)
+{
+ return false;
+}
+
int kvm_arch_vcpu_should_kick(struct kvm_vcpu *vcpu)
{
return 1;
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index af09d34..f78cdc2 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -2447,6 +2447,16 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu)
return kvm_s390_vcpu_has_irq(vcpu, 0);
}

+bool kvm_arch_vcpu_spin_in_kernel(struct kvm_vcpu *vcpu)
+{
+ return false;
+}
+
+bool kvm_arch_vcpu_preempt_in_kernel(struct kvm_vcpu *vcpu)
+{
+ return false;
+}
+
void kvm_s390_vcpu_block(struct kvm_vcpu *vcpu)
{
atomic_or(PROG_BLOCK_SIE, &vcpu->arch.sie_block->prog20);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 6c97c82..04c6a1f 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -8435,6 +8435,16 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu)
return kvm_vcpu_running(vcpu) || kvm_vcpu_has_events(vcpu);
}

+bool kvm_arch_vcpu_spin_in_kernel(struct kvm_vcpu *vcpu)
+{
+ return false;
+}
+
+bool kvm_arch_vcpu_preempt_in_kernel(struct kvm_vcpu *vcpu)
+{
+ return false;
+}
+
int kvm_arch_vcpu_should_kick(struct kvm_vcpu *vcpu)
{
return kvm_vcpu_exiting_guest_mode(vcpu) == IN_GUEST_MODE;
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 890b706..9613620 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -798,6 +798,8 @@ int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
void kvm_arch_hardware_unsetup(void);
void kvm_arch_check_processor_compat(void *rtn);
int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu);
+bool kvm_arch_vcpu_spin_in_kernel(struct kvm_vcpu *vcpu);
+bool kvm_arch_vcpu_preempt_in_kernel(struct kvm_vcpu *vcpu);
int kvm_arch_vcpu_should_kick(struct kvm_vcpu *vcpu);

#ifndef __KVM_HAVE_ARCH_VM_ALLOC
diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
index a39a1e1..e45f780 100644
--- a/virt/kvm/arm/arm.c
+++ b/virt/kvm/arm/arm.c
@@ -416,6 +416,16 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *v)
&& !v->arch.power_off && !v->arch.pause);
}

+bool kvm_arch_vcpu_spin_in_kernel(struct kvm_vcpu *vcpu)
+{
+ return false;
+}
+
+bool kvm_arch_vcpu_preempt_in_kernel(struct kvm_vcpu *vcpu)
+{
+ return false;
+}
+
/* Just ensure a guest exit from a particular CPU */
static void exit_vm_noop(void *info)
{
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index f3f7427..0d0527b 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -2324,12 +2324,14 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me)
{
struct kvm *kvm = me->kvm;
struct kvm_vcpu *vcpu;
+ bool in_kern;
int last_boosted_vcpu = me->kvm->last_boosted_vcpu;
int yielded = 0;
int try = 3;
int pass;
int i;

+ in_kern = kvm_arch_vcpu_spin_in_kernel(me);
kvm_vcpu_set_in_spin_loop(me, true);
/*
* We boost the priority of a VCPU that is runnable but not
@@ -2351,6 +2353,8 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me)
continue;
if (swait_active(&vcpu->wq) && !kvm_arch_vcpu_runnable(vcpu))
continue;
+ if (in_kern && !kvm_arch_vcpu_preempt_in_kernel(vcpu))
+ continue;
if (!kvm_vcpu_eligible_for_directed_yield(vcpu))
continue;

--
1.8.3.1

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