KVM/s390: Set preempted flag during vcpu wakeup and interrupt delivery

Commit "kvm: Record the preemption status of vcpus using preempt notifiers"
caused a performance regression on s390. It turned out that in the case that
if a former sleeping cpu, that was woken up, this cpu is not a yield candidate
since it gave up the cpu voluntarily. To retain this candiate its preempted
flag is set during wakeup and interrupt delivery time.

Significant performance measurement work and code analysis to solve this
issue was provided by Mao Chuan Li and his team in Beijing.

Signed-off-by: Michael Mueller <mimu@linux.vnet.ibm.com>
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
index 1848080c3f34..fff070bd0159 100644
--- a/arch/s390/kvm/interrupt.c
+++ b/arch/s390/kvm/interrupt.c
@@ -505,6 +505,7 @@ enum hrtimer_restart kvm_s390_idle_wakeup(struct hrtimer *timer)
         struct kvm_vcpu *vcpu;
 
         vcpu = container_of(timer, struct kvm_vcpu, arch.ckc_timer);
+        vcpu->preempted = true;
         tasklet_schedule(&vcpu->arch.tasklet);
 
         return HRTIMER_NORESTART;
@@ -732,6 +733,7 @@ static int __inject_vm(struct kvm *kvm, struct kvm_s390_interrupt_info *inti)
         atomic_set_mask(CPUSTAT_EXT_INT, li->cpuflags);
         if (waitqueue_active(li->wq))
                 wake_up_interruptible(li->wq);
+        kvm_get_vcpu(kvm, sigcpu)->preempted = true;
         spin_unlock_bh(&li->lock);
 unlock_fi:
         spin_unlock(&fi->lock);
@@ -877,6 +879,7 @@ int kvm_s390_inject_vcpu(struct kvm_vcpu *vcpu,
         atomic_set_mask(CPUSTAT_EXT_INT, li->cpuflags);
         if (waitqueue_active(&vcpu->wq))
                 wake_up_interruptible(&vcpu->wq);
+        vcpu->preempted = true;
         spin_unlock_bh(&li->lock);
         mutex_unlock(&vcpu->kvm->lock);
         return 0;