2022-12-01 02:12:02

by liujing

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

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 <[email protected]>
---
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

2022-12-02 19:48:42

by Paolo Bonzini

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

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