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@redhat.com

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@redhat.com Signed-off-by: Nitesh Narayan Lal nitesh@redhat.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com [borntraeger@de.ibm.com]: backport to 4.19 (also fits for 5.4) Signed-off-by: Christian Borntraeger borntraeger@de.ibm.com

---

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@redhat.com

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