On Tue, Sep 21, 2021 at 04:31:03PM +0200, Paolo Bonzini wrote:
> On 21/09/21 15:48, Christian Borntraeger wrote:
> > From: Radim Krčmář <rkrcmar@xxxxxxxxxx>
> >
> > Fetching an index for any vcpu in kvm->vcpus array by traversing
> > the entire array everytime is costly.
> > This patch remembers the position of each vcpu in kvm->vcpus array
> > by storing it in vcpus_idx under kvm_vcpu structure.
> >
> > Signed-off-by: Radim Krčmář <rkrcmar@xxxxxxxxxx>
> > Signed-off-by: Nitesh Narayan Lal <nitesh@xxxxxxxxxx>
> > Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> > [borntraeger@xxxxxxxxxx]: backport to 4.19 (also fits for 5.4)
> > Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
> > ---
> > include/linux/kvm_host.h | 11 +++--------
> > virt/kvm/kvm_main.c | 5 +++--
> > 2 files changed, 6 insertions(+), 10 deletions(-)
> >
> > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > index 8dd4ebb58e97..827f70ce0b49 100644
> > --- a/include/linux/kvm_host.h
> > +++ b/include/linux/kvm_host.h
> > @@ -248,7 +248,8 @@ struct kvm_vcpu {
> > struct preempt_notifier preempt_notifier;
> > #endif
> > int cpu;
> > - int vcpu_id;
> > + int vcpu_id; /* id given by userspace at creation */
> > + int vcpu_idx; /* index in kvm->vcpus array */
> > int srcu_idx;
> > int mode;
> > u64 requests;
> > @@ -551,13 +552,7 @@ static inline struct kvm_vcpu *kvm_get_vcpu_by_id(struct kvm *kvm, int id)
> > static inline int kvm_vcpu_get_idx(struct kvm_vcpu *vcpu)
> > {
> > - struct kvm_vcpu *tmp;
> > - int idx;
> > -
> > - kvm_for_each_vcpu(idx, tmp, vcpu->kvm)
> > - if (tmp == vcpu)
> > - return idx;
> > - BUG();
> > + return vcpu->vcpu_idx;
> > }
> > #define kvm_for_each_memslot(memslot, slots) \
> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index a3d82113ae1c..86ef740763b5 100644
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
> > @@ -2751,7 +2751,8 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, u32 id)
> > goto unlock_vcpu_destroy;
> > }
> > - BUG_ON(kvm->vcpus[atomic_read(&kvm->online_vcpus)]);
> > + vcpu->vcpu_idx = atomic_read(&kvm->online_vcpus);
> > + BUG_ON(kvm->vcpus[vcpu->vcpu_idx]);
> > /* Now it's all set up, let userspace reach it */
> > kvm_get_kvm(kvm);
> > @@ -2761,7 +2762,7 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, u32 id)
> > goto unlock_vcpu_destroy;
> > }
> > - kvm->vcpus[atomic_read(&kvm->online_vcpus)] = vcpu;
> > + kvm->vcpus[vcpu->vcpu_idx] = vcpu;
> > /*
> > * Pairs with smp_rmb() in kvm_get_vcpu. Write kvm->vcpus
> >
>
> Acked-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
>
> The backport makes sense given the code in the stable branch now calls
> kvm_vcpu_get_idx more than it used to.
Now queued up, thanks.
greg k-h
