Re: [patch -rt 1/2] KVM: use simple waitqueue for vcpu->wq

Marcelo Tosatti
2015-01-19T14:41:00Z

On Fri, Jan 16, 2015 at 11:48:46AM -0500, Steven Rostedt wrote:
> > @@ -971,8 +971,8 @@
> > kvm_mips_callbacks->queue_timer_int(vcpu);
> >
> > vcpu->arch.wait = 0;
> > - if (waitqueue_active(&vcpu->wq)) {
> > - wake_up_interruptible(&vcpu->wq);
> > + if (swaitqueue_active(&vcpu->wq)) {
> > + swait_wake_nterruptible(&vcpu->wq);
>
> Sure you compiled this patch?

Only x86.

> > Index: linux-stable-rt/arch/powerpc/include/asm/kvm_host.h
> > ===================================================================
> > --- linux-stable-rt.orig/arch/powerpc/include/asm/kvm_host.h 2014-11-25 14:13:39.193899944 -0200
> > +++ linux-stable-rt/arch/powerpc/include/asm/kvm_host.h 2014-11-25 14:14:38.621810091 -0200
> > @@ -295,7 +295,7 @@
> > u8 in_guest;
> > struct list_head runnable_threads;
> > spinlock_t lock;
> > - wait_queue_head_t wq;
> > + struct swait_head wq;
> > u64 stolen_tb;
> > u64 preempt_tb;
> > struct kvm_vcpu *runner;
> > @@ -612,7 +612,7 @@
> > u8 prodded;
> > u32 last_inst;
> >
> > - wait_queue_head_t *wqp;
> > + struct swait_head *wqp;
> > struct kvmppc_vcore *vcore;
> > int ret;
> > int trap;
> > Index: linux-stable-rt/arch/powerpc/kvm/book3s_hv.c
> > ===================================================================
> > --- linux-stable-rt.orig/arch/powerpc/kvm/book3s_hv.c 2014-11-25 14:13:39.195899942 -0200
> > +++ linux-stable-rt/arch/powerpc/kvm/book3s_hv.c 2014-11-25 14:14:38.625810085 -0200
> > @@ -74,11 +74,11 @@
> > {
> > int me;
> > int cpu = vcpu->cpu;
> > - wait_queue_head_t *wqp;
> > + struct swait_head *wqp;
> >
> > wqp = kvm_arch_vcpu_wq(vcpu);
> > - if (waitqueue_active(wqp)) {
> > - wake_up_interruptible(wqp);
> > + if (swaitqueue_active(wqp)) {
> > + swait_wake_interruptible(wqp);
> > ++vcpu->stat.halt_wakeup;
> > }
> >
> > @@ -583,8 +583,8 @@
> > tvcpu->arch.prodded = 1;
> > smp_mb();
> > if (vcpu->arch.ceded) {
> > - if (waitqueue_active(&vcpu->wq)) {
> > - wake_up_interruptible(&vcpu->wq);
> > + if (swaitqueue_active(&vcpu->wq)) {
> > + swait_wake_interruptible(&vcpu->wq);
> > vcpu->stat.halt_wakeup++;
> > }
> > }
> > @@ -1199,7 +1199,7 @@
> > if (vcore) {
> > INIT_LIST_HEAD(&vcore->runnable_threads);
> > spin_lock_init(&vcore->lock);
> > - init_waitqueue_head(&vcore->wq);
> > + init_swait_head(&vcore->wq);
> > vcore->preempt_tb = TB_NIL;
> > vcore->lpcr = kvm->arch.lpcr;
> > vcore->first_vcpuid = core * threads_per_core;
> > @@ -1566,13 +1566,13 @@
> > */
> > static void kvmppc_vcore_blocked(struct kvmppc_vcore *vc)
> > {
> > - DEFINE_WAIT(wait);
> > + DEFINE_SWAITER(wait);
> >
> > - prepare_to_wait(&vc->wq, &wait, TASK_INTERRUPTIBLE);
> > + swait_prepare(&vc->wq, &wait, TASK_INTERRUPTIBLE);
> > vc->vcore_state = VCORE_SLEEPING;
> > spin_unlock(&vc->lock);
> > schedule();
> > - finish_wait(&vc->wq, &wait);
> > + swait_finish(&vc->wq, &wait);
> > spin_lock(&vc->lock);
> > vc->vcore_state = VCORE_INACTIVE;
> > }
> > @@ -1613,7 +1613,7 @@
> > kvmppc_create_dtl_entry(vcpu, vc);
> > kvmppc_start_thread(vcpu);
> > } else if (vc->vcore_state == VCORE_SLEEPING) {
> > - wake_up(&vc->wq);
> > + swait_wake(&vc->wq);
>
> I notice everywhere you have a swait_wake_interruptible() but here. Is
> there a reason why?
>
> IIRC, Peter wants to make swait wakeup usage homogenous. That is, you
> either sleep in an interruptible state, or you don't. You can't mix and
> match it.

IIUC there is only one waiter on this waitqueue at any given time.

Paul is that correct?