[PATCH] KVM: x86: Optimize your code to avoid unnecessary calls

[PATCH] KVM: x86: Optimize your code to avoid unnecessary calls

[liujing]

In the kvm_vm_ioctl_get_irqchip function, we can removethe 
definition of the r variable instead of return 0 in the end.
In the kvm_vm_ioctl_set_irqchip function, also use return 0 instead,
return -EINVAL to avoid calling kvm_pic_update_irq again.

Signed-off-by: liujing <liujing@cmss.chinamobile.com>
---
 arch/x86/kvm/x86.c | 16 +++++-----------
 1 file changed, 5 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 2835bd796639..8e94f3d730ee 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6002,9 +6002,7 @@ static unsigned long kvm_vm_ioctl_get_nr_mmu_pages(struct kvm *kvm)
 static int kvm_vm_ioctl_get_irqchip(struct kvm *kvm, struct kvm_irqchip *chip)
 {
 	struct kvm_pic *pic = kvm->arch.vpic;
-	int r;
 
-	r = 0;
 	switch (chip->chip_id) {
 	case KVM_IRQCHIP_PIC_MASTER:
 		memcpy(&chip->chip.pic, &pic->pics[0],
@@ -6018,18 +6016,15 @@ static int kvm_vm_ioctl_get_irqchip(struct kvm *kvm, struct kvm_irqchip *chip)
 		kvm_get_ioapic(kvm, &chip->chip.ioapic);
 		break;
 	default:
-		r = -EINVAL;
-		break;
+		return -EINVAL;
 	}
-	return r;
+	return 0;
 }
 
 static int kvm_vm_ioctl_set_irqchip(struct kvm *kvm, struct kvm_irqchip *chip)
 {
 	struct kvm_pic *pic = kvm->arch.vpic;
-	int r;
-
-	r = 0;	
 	switch (chip->chip_id) {
 	case KVM_IRQCHIP_PIC_MASTER:
 		spin_lock(&pic->lock);
@@ -6047,11 +6042,10 @@ static int kvm_vm_ioctl_set_irqchip(struct kvm *kvm, struct kvm_irqchip *chip)
 		kvm_set_ioapic(kvm, &chip->chip.ioapic);
 		break;
 	default:
-		r = -EINVAL;
-		break;
+		return -EINVAL;
 	}
 	kvm_pic_update_irq(pic);
-	return r;
+	return 0;
 }
 
 static int kvm_vm_ioctl_get_pit(struct kvm *kvm, struct kvm_pit_state *ps)
-- 
2.18.2

Re: [PATCH] KVM: x86: Optimize your code to avoid unnecessary calls

[Paolo Bonzini]

Hi,

thanks for your contribution!  We can improve the code even further 
though.  You are still calling kvm_pic_update_irq() after 
kvm_set_ioapic(), and that is also unnecessary.

On 12/1/22 02:42, liujing wrote:
> @@ -6047,11 +6042,10 @@ static int kvm_vm_ioctl_set_irqchip(struct kvm *kvm, struct kvm_irqchip *chip)
>   		kvm_set_ioapic(kvm, &chip->chip.ioapic);
>   		break;
>   	default:
> -		r = -EINVAL;
> -		break;
> +		return -EINVAL;
>   	}
>   	kvm_pic_update_irq(pic);
> -	return r;

Please make instead a new function:

void
kvm_set_pic(struct kvm *kvm, int n, struct kvm_pic_state *state)
{
	struct kvm_pic *s = kvm->arch.vpic;

	pic_lock(s);
	memcpy(...)
	pic_update_irq(s);
	pic_unlock(s);
}

that lets you replace kvm_pic_update_irq() altogether.

Thanks!

Paolo