Re: [PATCH] KVM: Optimize kvm_arch_vcpu_ioctl_run function

[Tianjia Zhang]

On 2020/4/13 16:56, Marc Zyngier wrote:
> Tianjia,
>
> On 2020-04-13 04:45, Tianjia Zhang wrote:
> > kvm_arch_vcpu_ioctl_run() is only called in the file kvm_main.c,
> > where vcpu->run is the kvm_run parameter, so it has been replaced.
> >
> > Signed-off-by: Tianjia Zhang <tianjia.zhang@xxxxxxxxxxxxxxxxx>
> > ---
> > Âarch/x86/kvm/x86.c | 8 ++++----
> > Âvirt/kvm/arm/arm.c | 2 +-
> > Â2 files changed, 5 insertions(+), 5 deletions(-)
> >
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 3bf2ecafd027..70e3f4abbd4d 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -8726,18 +8726,18 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu
> > *vcpu, struct kvm_run *kvm_run)
> > ÂÂÂÂÂÂÂÂ r = -EAGAIN;
> > ÂÂÂÂÂÂÂÂ if (signal_pending(current)) {
> > ÂÂÂÂÂÂÂÂÂÂÂÂ r = -EINTR;
> > -ÂÂÂÂÂÂÂÂÂÂÂ vcpu->run->exit_reason = KVM_EXIT_INTR;
> > +ÂÂÂÂÂÂÂÂÂÂÂ kvm_run->exit_reason = KVM_EXIT_INTR;
> > ÂÂÂÂÂÂÂÂÂÂÂÂ ++vcpu->stat.signal_exits;
> > ÂÂÂÂÂÂÂÂ }
> > ÂÂÂÂÂÂÂÂ goto out;
> > ÂÂÂÂ }
> >
> > -ÂÂÂ if (vcpu->run->kvm_valid_regs & ~KVM_SYNC_X86_VALID_FIELDS) {
> > +ÂÂÂ if (kvm_run->kvm_valid_regs & ~KVM_SYNC_X86_VALID_FIELDS) {
> > ÂÂÂÂÂÂÂÂ r = -EINVAL;
> > ÂÂÂÂÂÂÂÂ goto out;
> > ÂÂÂÂ }
> >
> > -ÂÂÂ if (vcpu->run->kvm_dirty_regs) {
> > +ÂÂÂ if (kvm_run->kvm_dirty_regs) {
> > ÂÂÂÂÂÂÂÂ r = sync_regs(vcpu);
> > ÂÂÂÂÂÂÂÂ if (r != 0)
> > ÂÂÂÂÂÂÂÂÂÂÂÂ goto out;
> > @@ -8767,7 +8767,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu
> > *vcpu, struct kvm_run *kvm_run)
> >
> > Âout:
> > ÂÂÂÂ kvm_put_guest_fpu(vcpu);
> > -ÂÂÂ if (vcpu->run->kvm_valid_regs)
> > +ÂÂÂ if (kvm_run->kvm_valid_regs)
> > ÂÂÂÂÂÂÂÂ store_regs(vcpu);
> > ÂÂÂÂ post_kvm_run_save(vcpu);
> > ÂÂÂÂ kvm_sigset_deactivate(vcpu);
> > diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
> > index 48d0ec44ad77..ab9d7966a4c8 100644
> > --- a/virt/kvm/arm/arm.c
> > +++ b/virt/kvm/arm/arm.c
> > @@ -659,7 +659,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu,
> > struct kvm_run *run)
> > ÂÂÂÂÂÂÂÂ return ret;
> >
> > ÂÂÂÂ if (run->exit_reason == KVM_EXIT_MMIO) {
> > -ÂÂÂÂÂÂÂ ret = kvm_handle_mmio_return(vcpu, vcpu->run);
> > +ÂÂÂÂÂÂÂ ret = kvm_handle_mmio_return(vcpu, run);
> > ÂÂÂÂÂÂÂÂ if (ret)
> > ÂÂÂÂÂÂÂÂÂÂÂÂ return ret;
> > ÂÂÂÂ }
>
> Do you have any number supporting the idea that you are optimizing anything
> here? Performance, code size, register pressure or any other relevant 
> metric?
>
> Thanks,
>
>  ÂÂÂÂÂÂÂ M.

This is only a simplified implementation of the function, the impact on 
performance and register pressure can be ignored.

Thanks,
Tianjia