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KVM: add spinlock optimization framework

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If a vcpu exits due to request a user mode spinlock, then
the spinlock-holder may be preempted in user mode or kernel mode.
(Note that not all architectures trap spin loops in user mode,
only AMD x86 and ARM/ARM64 currently do).

But if a vcpu exits in kernel mode, then the holder must be
preempted in kernel mode, so we should choose a vcpu in kernel mode
as a more likely candidate for the lock holder.

This introduces kvm_arch_vcpu_in_kernel() to decide whether the
vcpu is in kernel-mode when it's preempted.  kvm_vcpu_on_spin's
new argument says the same of the spinning VCPU.

Signed-off-by: Longpeng(Mike) <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>
This commit is contained in:
Longpeng(Mike) 2017-08-08 12:05:32 +08:00 • committed by Paolo Bonzini
commit 199b5763d3
13 changed files with 36 additions and 8 deletions
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5
virt/kvm/arm/arm.c
View file

@ -416,6 +416,11 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *v)
&& !v->arch.power_off && !v->arch.pause);
}
bool kvm_arch_vcpu_in_kernel(struct kvm_vcpu *vcpu)
{
return false;
}
/* Just ensure a guest exit from a particular CPU */
static void exit_vm_noop(void *info)
{

4
virt/kvm/kvm_main.c
View file

@ -2317,7 +2317,7 @@ static bool kvm_vcpu_eligible_for_directed_yield(struct kvm_vcpu *vcpu)
#endif
}
void kvm_vcpu_on_spin(struct kvm_vcpu *me)
void kvm_vcpu_on_spin(struct kvm_vcpu *me, bool yield_to_kernel_mode)
{
struct kvm *kvm = me->kvm;
struct kvm_vcpu *vcpu;
@ -2348,6 +2348,8 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me)
continue;
if (swait_active(&vcpu->wq) && !kvm_arch_vcpu_runnable(vcpu))
continue;
if (yield_to_kernel_mode && !kvm_arch_vcpu_in_kernel(vcpu))
continue;
if (!kvm_vcpu_eligible_for_directed_yield(vcpu))
continue;