KVM: s390: enable IBS for single running VCPUs
This patch enables the IBS facility when a single VCPU is running.
The facility is dynamically turned on/off as soon as other VCPUs
enter/leave the stopped state.
When this facility is operating, some instructions can be executed
faster for single-cpu guests.
Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Reviewed-by: Dominik Dingel <dingel@linux.vnet.ibm.com>
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 6c972d2..0a01744 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -458,6 +458,8 @@
kvm->arch.css_support = 0;
kvm->arch.use_irqchip = 0;
+ spin_lock_init(&kvm->arch.start_stop_lock);
+
return 0;
out_nogmap:
debug_unregister(kvm->arch.dbf);
@@ -996,8 +998,15 @@
return true;
}
+static bool ibs_enabled(struct kvm_vcpu *vcpu)
+{
+ return atomic_read(&vcpu->arch.sie_block->cpuflags) & CPUSTAT_IBS;
+}
+
static int kvm_s390_handle_requests(struct kvm_vcpu *vcpu)
{
+retry:
+ s390_vcpu_unblock(vcpu);
/*
* We use MMU_RELOAD just to re-arm the ipte notifier for the
* guest prefix page. gmap_ipte_notify will wait on the ptl lock.
@@ -1005,15 +1014,34 @@
* already finished. We might race against a second unmapper that
* wants to set the blocking bit. Lets just retry the request loop.
*/
- while (kvm_check_request(KVM_REQ_MMU_RELOAD, vcpu)) {
+ if (kvm_check_request(KVM_REQ_MMU_RELOAD, vcpu)) {
int rc;
rc = gmap_ipte_notify(vcpu->arch.gmap,
vcpu->arch.sie_block->prefix,
PAGE_SIZE * 2);
if (rc)
return rc;
- s390_vcpu_unblock(vcpu);
+ goto retry;
}
+
+ if (kvm_check_request(KVM_REQ_ENABLE_IBS, vcpu)) {
+ if (!ibs_enabled(vcpu)) {
+ trace_kvm_s390_enable_disable_ibs(vcpu->vcpu_id, 1);
+ atomic_set_mask(CPUSTAT_IBS,
+ &vcpu->arch.sie_block->cpuflags);
+ }
+ goto retry;
+ }
+
+ if (kvm_check_request(KVM_REQ_DISABLE_IBS, vcpu)) {
+ if (ibs_enabled(vcpu)) {
+ trace_kvm_s390_enable_disable_ibs(vcpu->vcpu_id, 0);
+ atomic_clear_mask(CPUSTAT_IBS,
+ &vcpu->arch.sie_block->cpuflags);
+ }
+ goto retry;
+ }
+
return 0;
}
@@ -1362,16 +1390,107 @@
return kvm_s390_store_status_unloaded(vcpu, addr);
}
+static inline int is_vcpu_stopped(struct kvm_vcpu *vcpu)
+{
+ return atomic_read(&(vcpu)->arch.sie_block->cpuflags) & CPUSTAT_STOPPED;
+}
+
+static void __disable_ibs_on_vcpu(struct kvm_vcpu *vcpu)
+{
+ kvm_check_request(KVM_REQ_ENABLE_IBS, vcpu);
+ kvm_make_request(KVM_REQ_DISABLE_IBS, vcpu);
+ exit_sie_sync(vcpu);
+}
+
+static void __disable_ibs_on_all_vcpus(struct kvm *kvm)
+{
+ unsigned int i;
+ struct kvm_vcpu *vcpu;
+
+ kvm_for_each_vcpu(i, vcpu, kvm) {
+ __disable_ibs_on_vcpu(vcpu);
+ }
+}
+
+static void __enable_ibs_on_vcpu(struct kvm_vcpu *vcpu)
+{
+ kvm_check_request(KVM_REQ_DISABLE_IBS, vcpu);
+ kvm_make_request(KVM_REQ_ENABLE_IBS, vcpu);
+ exit_sie_sync(vcpu);
+}
+
void kvm_s390_vcpu_start(struct kvm_vcpu *vcpu)
{
+ int i, online_vcpus, started_vcpus = 0;
+
+ if (!is_vcpu_stopped(vcpu))
+ return;
+
trace_kvm_s390_vcpu_start_stop(vcpu->vcpu_id, 1);
+ /* Only one cpu at a time may enter/leave the STOPPED state. */
+ spin_lock_bh(&vcpu->kvm->arch.start_stop_lock);
+ online_vcpus = atomic_read(&vcpu->kvm->online_vcpus);
+
+ for (i = 0; i < online_vcpus; i++) {
+ if (!is_vcpu_stopped(vcpu->kvm->vcpus[i]))
+ started_vcpus++;
+ }
+
+ if (started_vcpus == 0) {
+ /* we're the only active VCPU -> speed it up */
+ __enable_ibs_on_vcpu(vcpu);
+ } else if (started_vcpus == 1) {
+ /*
+ * As we are starting a second VCPU, we have to disable
+ * the IBS facility on all VCPUs to remove potentially
+ * oustanding ENABLE requests.
+ */
+ __disable_ibs_on_all_vcpus(vcpu->kvm);
+ }
+
atomic_clear_mask(CPUSTAT_STOPPED, &vcpu->arch.sie_block->cpuflags);
+ /*
+ * Another VCPU might have used IBS while we were offline.
+ * Let's play safe and flush the VCPU at startup.
+ */
+ vcpu->arch.sie_block->ihcpu = 0xffff;
+ spin_unlock_bh(&vcpu->kvm->arch.start_stop_lock);
+ return;
}
void kvm_s390_vcpu_stop(struct kvm_vcpu *vcpu)
{
+ int i, online_vcpus, started_vcpus = 0;
+ struct kvm_vcpu *started_vcpu = NULL;
+
+ if (is_vcpu_stopped(vcpu))
+ return;
+
trace_kvm_s390_vcpu_start_stop(vcpu->vcpu_id, 0);
+ /* Only one cpu at a time may enter/leave the STOPPED state. */
+ spin_lock_bh(&vcpu->kvm->arch.start_stop_lock);
+ online_vcpus = atomic_read(&vcpu->kvm->online_vcpus);
+
atomic_set_mask(CPUSTAT_STOPPED, &vcpu->arch.sie_block->cpuflags);
+ __disable_ibs_on_vcpu(vcpu);
+
+ for (i = 0; i < online_vcpus; i++) {
+ if (!is_vcpu_stopped(vcpu->kvm->vcpus[i])) {
+ started_vcpus++;
+ started_vcpu = vcpu->kvm->vcpus[i];
+ }
+ }
+
+ if (started_vcpus == 1) {
+ /*
+ * As we only have one VCPU left, we want to enable the
+ * IBS facility for that VCPU to speed it up.
+ */
+ __enable_ibs_on_vcpu(started_vcpu);
+ }
+
+ spin_unlock_bh(&vcpu->kvm->arch.start_stop_lock);
+ return;
}
static int kvm_vcpu_ioctl_enable_cap(struct kvm_vcpu *vcpu,