This lock is only intended to prevent racing with closing an event
channel - evtchn_set_pending() doesn''t require external serialization.
Signed-off-by: Jan Beulich <jbeulich@novell.com>
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -147,7 +147,7 @@ struct vcpu *alloc_vcpu(
v->domain = d;
v->vcpu_id = vcpu_id;
- spin_lock_init(&v->virq_lock);
+ rwlock_init(&v->virq_lock);
tasklet_init(&v->continue_hypercall_tasklet, NULL, 0);
--- a/xen/common/event_channel.c
+++ b/xen/common/event_channel.c
@@ -417,7 +417,7 @@ static long __evtchn_close(struct domain
if ( v->virq_to_evtchn[chn1->u.virq] != port1 )
continue;
v->virq_to_evtchn[chn1->u.virq] = 0;
- spin_barrier_irq(&v->virq_lock);
+ write_barrier_irq(&v->virq_lock);
}
break;
@@ -613,12 +613,11 @@ int guest_enabled_event(struct vcpu *v,
void send_guest_vcpu_virq(struct vcpu *v, int virq)
{
- unsigned long flags;
int port;
ASSERT(!virq_is_global(virq));
- spin_lock_irqsave(&v->virq_lock, flags);
+ read_lock(&v->virq_lock);
port = v->virq_to_evtchn[virq];
if ( unlikely(port == 0) )
@@ -627,12 +626,11 @@ void send_guest_vcpu_virq(struct vcpu *v
evtchn_set_pending(v, port);
out:
- spin_unlock_irqrestore(&v->virq_lock, flags);
+ read_unlock(&v->virq_lock);
}
void send_guest_global_virq(struct domain *d, int virq)
{
- unsigned long flags;
int port;
struct vcpu *v;
struct evtchn *chn;
@@ -646,7 +644,7 @@ void send_guest_global_virq(struct domai
if ( unlikely(v == NULL) )
return;
- spin_lock_irqsave(&v->virq_lock, flags);
+ read_lock(&v->virq_lock);
port = v->virq_to_evtchn[virq];
if ( unlikely(port == 0) )
@@ -656,7 +654,7 @@ void send_guest_global_virq(struct domai
evtchn_set_pending(d->vcpu[chn->notify_vcpu_id], port);
out:
- spin_unlock_irqrestore(&v->virq_lock, flags);
+ read_unlock(&v->virq_lock);
}
int send_guest_pirq(struct domain *d, int pirq)
--- a/xen/common/spinlock.c
+++ b/xen/common/spinlock.c
@@ -344,6 +344,20 @@ int _rw_is_write_locked(rwlock_t *lock)
return _raw_rw_is_write_locked(&lock->raw);
}
+void _write_barrier(rwlock_t *lock)
+{
+ check_lock(&lock->debug);
+ do { mb(); } while ( _raw_rw_is_locked(&lock->raw) );
+}
+
+void _write_barrier_irq(rwlock_t *lock)
+{
+ unsigned long flags;
+ local_irq_save(flags);
+ _write_barrier(lock);
+ local_irq_restore(flags);
+}
+
#ifdef LOCK_PROFILE
struct lock_profile_anc {
--- a/xen/include/xen/sched.h
+++ b/xen/include/xen/sched.h
@@ -157,9 +157,12 @@ struct vcpu
unsigned long pause_flags;
atomic_t pause_count;
- /* IRQ-safe virq_lock protects against delivering VIRQ to stale evtchn. */
+ /*
+ * Writer-side-IRQ-safe virq_lock protects against delivering VIRQ
+ * to stale evtchn.
+ */
u16 virq_to_evtchn[NR_VIRQS];
- spinlock_t virq_lock;
+ rwlock_t virq_lock;
/* Bitmask of CPUs on which this VCPU may run. */
cpumask_t cpu_affinity;
--- a/xen/include/xen/spinlock.h
+++ b/xen/include/xen/spinlock.h
@@ -170,6 +170,9 @@ void _write_unlock_irqrestore(rwlock_t *
int _rw_is_locked(rwlock_t *lock);
int _rw_is_write_locked(rwlock_t *lock);
+void _write_barrier(rwlock_t *lock);
+void _write_barrier_irq(rwlock_t *lock);
+
#define spin_lock(l) _spin_lock(l)
#define spin_lock_irq(l) _spin_lock_irq(l)
#define spin_lock_irqsave(l, f) ((f) = _spin_lock_irqsave(l))
@@ -223,4 +226,7 @@ int _rw_is_write_locked(rwlock_t *lock);
#define rw_is_locked(l) _rw_is_locked(l)
#define rw_is_write_locked(l) _rw_is_write_locked(l)
+#define write_barrier(l) _write_barrier(l)
+#define write_barrier_irq(l) _write_barrier_irq(l)
+
#endif /* __SPINLOCK_H__ */
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Keir Fraser
2011-Mar-26 09:29 UTC
Re: [Xen-devel] [PATCH] convert vcpu''s virq_lock to rwlock
On 25/03/2011 16:53, "Jan Beulich" <JBeulich@novell.com> wrote:> This lock is only intended to prevent racing with closing an event > channel - evtchn_set_pending() doesn''t require external serialization.Still a small critical section, I doubt the serialisation matters compared with the cost of an extra LOCKed operation on read_unlock(). Especially since the lock is per-vcpu anyway and the only at-all common VIRQ is VIRQ_TIMER. The probability of unnecessary serialisation being a bottleneck here is basically zero. We can get rid of the local_irq_save/restore operations though (at the cost of changing the lock debug checks in spinlock.c because the send_*_virq functions can be called both with IRQs disabled and enabled, so as-is the patch could make us bug out on the checks). But, overall, worth it? I doubt EFLAGS.IF fiddling compares unfavourably with an extra LOCKed operation, cost wise. So, I''m not even slightly convinced. I''ll leave as is. -- Keir> Signed-off-by: Jan Beulich <jbeulich@novell.com> > > --- a/xen/common/domain.c > +++ b/xen/common/domain.c > @@ -147,7 +147,7 @@ struct vcpu *alloc_vcpu( > v->domain = d; > v->vcpu_id = vcpu_id; > > - spin_lock_init(&v->virq_lock); > + rwlock_init(&v->virq_lock); > > tasklet_init(&v->continue_hypercall_tasklet, NULL, 0); > > --- a/xen/common/event_channel.c > +++ b/xen/common/event_channel.c > @@ -417,7 +417,7 @@ static long __evtchn_close(struct domain > if ( v->virq_to_evtchn[chn1->u.virq] != port1 ) > continue; > v->virq_to_evtchn[chn1->u.virq] = 0; > - spin_barrier_irq(&v->virq_lock); > + write_barrier_irq(&v->virq_lock); > } > break; > > @@ -613,12 +613,11 @@ int guest_enabled_event(struct vcpu *v, > > void send_guest_vcpu_virq(struct vcpu *v, int virq) > { > - unsigned long flags; > int port; > > ASSERT(!virq_is_global(virq)); > > - spin_lock_irqsave(&v->virq_lock, flags); > + read_lock(&v->virq_lock); > > port = v->virq_to_evtchn[virq]; > if ( unlikely(port == 0) ) > @@ -627,12 +626,11 @@ void send_guest_vcpu_virq(struct vcpu *v > evtchn_set_pending(v, port); > > out: > - spin_unlock_irqrestore(&v->virq_lock, flags); > + read_unlock(&v->virq_lock); > } > > void send_guest_global_virq(struct domain *d, int virq) > { > - unsigned long flags; > int port; > struct vcpu *v; > struct evtchn *chn; > @@ -646,7 +644,7 @@ void send_guest_global_virq(struct domai > if ( unlikely(v == NULL) ) > return; > > - spin_lock_irqsave(&v->virq_lock, flags); > + read_lock(&v->virq_lock); > > port = v->virq_to_evtchn[virq]; > if ( unlikely(port == 0) ) > @@ -656,7 +654,7 @@ void send_guest_global_virq(struct domai > evtchn_set_pending(d->vcpu[chn->notify_vcpu_id], port); > > out: > - spin_unlock_irqrestore(&v->virq_lock, flags); > + read_unlock(&v->virq_lock); > } > > int send_guest_pirq(struct domain *d, int pirq) > --- a/xen/common/spinlock.c > +++ b/xen/common/spinlock.c > @@ -344,6 +344,20 @@ int _rw_is_write_locked(rwlock_t *lock) > return _raw_rw_is_write_locked(&lock->raw); > } > > +void _write_barrier(rwlock_t *lock) > +{ > + check_lock(&lock->debug); > + do { mb(); } while ( _raw_rw_is_locked(&lock->raw) ); > +} > + > +void _write_barrier_irq(rwlock_t *lock) > +{ > + unsigned long flags; > + local_irq_save(flags); > + _write_barrier(lock); > + local_irq_restore(flags); > +} > + > #ifdef LOCK_PROFILE > > struct lock_profile_anc { > --- a/xen/include/xen/sched.h > +++ b/xen/include/xen/sched.h > @@ -157,9 +157,12 @@ struct vcpu > unsigned long pause_flags; > atomic_t pause_count; > > - /* IRQ-safe virq_lock protects against delivering VIRQ to stale evtchn. > */ > + /* > + * Writer-side-IRQ-safe virq_lock protects against delivering VIRQ > + * to stale evtchn. > + */ > u16 virq_to_evtchn[NR_VIRQS]; > - spinlock_t virq_lock; > + rwlock_t virq_lock; > > /* Bitmask of CPUs on which this VCPU may run. */ > cpumask_t cpu_affinity; > --- a/xen/include/xen/spinlock.h > +++ b/xen/include/xen/spinlock.h > @@ -170,6 +170,9 @@ void _write_unlock_irqrestore(rwlock_t * > int _rw_is_locked(rwlock_t *lock); > int _rw_is_write_locked(rwlock_t *lock); > > +void _write_barrier(rwlock_t *lock); > +void _write_barrier_irq(rwlock_t *lock); > + > #define spin_lock(l) _spin_lock(l) > #define spin_lock_irq(l) _spin_lock_irq(l) > #define spin_lock_irqsave(l, f) ((f) = _spin_lock_irqsave(l)) > @@ -223,4 +226,7 @@ int _rw_is_write_locked(rwlock_t *lock); > #define rw_is_locked(l) _rw_is_locked(l) > #define rw_is_write_locked(l) _rw_is_write_locked(l) > > +#define write_barrier(l) _write_barrier(l) > +#define write_barrier_irq(l) _write_barrier_irq(l) > + > #endif /* __SPINLOCK_H__ */ > > > > _______________________________________________ > Xen-devel mailing list > Xen-devel@lists.xensource.com > http://lists.xensource.com/xen-devel_______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel