Michael S. Tsirkin
2022-Apr-25 08:08 UTC
[PATCH V3 6/9] virtio-ccw: implement synchronize_cbs()
On Mon, Apr 25, 2022 at 10:44:15AM +0800, Jason Wang wrote:> This patch tries to implement the synchronize_cbs() for ccw. For the > vring_interrupt() that is called via virtio_airq_handler(), the > synchronization is simply done via the airq_info's lock. For the > vring_interrupt() that is called via virtio_ccw_int_handler(), a per > device spinlock for irq is introduced ans used in the synchronization > method. > > Cc: Thomas Gleixner <tglx at linutronix.de> > Cc: Peter Zijlstra <peterz at infradead.org> > Cc: "Paul E. McKenney" <paulmck at kernel.org> > Cc: Marc Zyngier <maz at kernel.org> > Cc: Halil Pasic <pasic at linux.ibm.com> > Cc: Cornelia Huck <cohuck at redhat.com> > Signed-off-by: Jason Wang <jasowang at redhat.com>This is the only one that is giving me pause. Halil, Cornelia, should we be concerned about the performance impact here? Any chance it can be tested?> --- > drivers/s390/virtio/virtio_ccw.c | 27 +++++++++++++++++++++++++++ > 1 file changed, 27 insertions(+) > > diff --git a/drivers/s390/virtio/virtio_ccw.c b/drivers/s390/virtio/virtio_ccw.c > index d35e7a3f7067..c19f07a82d62 100644 > --- a/drivers/s390/virtio/virtio_ccw.c > +++ b/drivers/s390/virtio/virtio_ccw.c > @@ -62,6 +62,7 @@ struct virtio_ccw_device { > unsigned int revision; /* Transport revision */ > wait_queue_head_t wait_q; > spinlock_t lock; > + spinlock_t irq_lock; > struct mutex io_lock; /* Serializes I/O requests */ > struct list_head virtqueues; > bool is_thinint; > @@ -984,6 +985,27 @@ static const char *virtio_ccw_bus_name(struct virtio_device *vdev) > return dev_name(&vcdev->cdev->dev); > } > > +static void virtio_ccw_synchronize_cbs(struct virtio_device *vdev) > +{ > + struct virtio_ccw_device *vcdev = to_vc_device(vdev); > + struct airq_info *info = vcdev->airq_info; > + > + /* > + * Synchronize with the vring_interrupt() called by > + * virtio_ccw_int_handler(). > + */ > + spin_lock(&vcdev->irq_lock); > + spin_unlock(&vcdev->irq_lock); > + > + if (info) { > + /* > + * Synchronize with the vring_interrupt() with airq indicator > + */ > + write_lock(&info->lock); > + write_unlock(&info->lock); > + } > +} > + > static const struct virtio_config_ops virtio_ccw_config_ops = { > .get_features = virtio_ccw_get_features, > .finalize_features = virtio_ccw_finalize_features, > @@ -995,6 +1017,7 @@ static const struct virtio_config_ops virtio_ccw_config_ops = { > .find_vqs = virtio_ccw_find_vqs, > .del_vqs = virtio_ccw_del_vqs, > .bus_name = virtio_ccw_bus_name, > + .synchronize_cbs = virtio_ccw_synchronize_cbs, > }; > > > @@ -1079,6 +1102,7 @@ static void virtio_ccw_int_handler(struct ccw_device *cdev, > { > __u32 activity = intparm & VIRTIO_CCW_INTPARM_MASK; > struct virtio_ccw_device *vcdev = dev_get_drvdata(&cdev->dev); > + unsigned long flags; > int i; > struct virtqueue *vq; > > @@ -1106,6 +1130,7 @@ static void virtio_ccw_int_handler(struct ccw_device *cdev, > vcdev->err = -EIO; > } > virtio_ccw_check_activity(vcdev, activity); > + spin_lock_irqsave(&vcdev->irq_lock, flags); > for_each_set_bit(i, indicators(vcdev), > sizeof(*indicators(vcdev)) * BITS_PER_BYTE) { > /* The bit clear must happen before the vring kick. */ > @@ -1114,6 +1139,7 @@ static void virtio_ccw_int_handler(struct ccw_device *cdev, > vq = virtio_ccw_vq_by_ind(vcdev, i); > vring_interrupt(0, vq); > } > + spin_unlock_irqrestore(&vcdev->irq_lock, flags); > if (test_bit(0, indicators2(vcdev))) { > virtio_config_changed(&vcdev->vdev); > clear_bit(0, indicators2(vcdev)); > @@ -1284,6 +1310,7 @@ static int virtio_ccw_online(struct ccw_device *cdev) > init_waitqueue_head(&vcdev->wait_q); > INIT_LIST_HEAD(&vcdev->virtqueues); > spin_lock_init(&vcdev->lock); > + spin_lock_init(&vcdev->irq_lock); > mutex_init(&vcdev->io_lock); > > spin_lock_irqsave(get_ccwdev_lock(cdev), flags); > -- > 2.25.1
Cornelia Huck
2022-Apr-25 08:54 UTC
[PATCH V3 6/9] virtio-ccw: implement synchronize_cbs()
On Mon, Apr 25 2022, "Michael S. Tsirkin" <mst at redhat.com> wrote:> On Mon, Apr 25, 2022 at 10:44:15AM +0800, Jason Wang wrote: >> This patch tries to implement the synchronize_cbs() for ccw. For the >> vring_interrupt() that is called via virtio_airq_handler(), the >> synchronization is simply done via the airq_info's lock. For the >> vring_interrupt() that is called via virtio_ccw_int_handler(), a per >> device spinlock for irq is introduced ans used in the synchronization >> method. >> >> Cc: Thomas Gleixner <tglx at linutronix.de> >> Cc: Peter Zijlstra <peterz at infradead.org> >> Cc: "Paul E. McKenney" <paulmck at kernel.org> >> Cc: Marc Zyngier <maz at kernel.org> >> Cc: Halil Pasic <pasic at linux.ibm.com> >> Cc: Cornelia Huck <cohuck at redhat.com> >> Signed-off-by: Jason Wang <jasowang at redhat.com> > > > This is the only one that is giving me pause. Halil, Cornelia, > should we be concerned about the performance impact here? > Any chance it can be tested?We can have a bunch of devices using the same airq structure, and the sync cb creates a choke point, same as registering/unregistering. If invoking the sync cb is a rare operation (same as (un)registering), it should not affect interrupt processing for other devices too much, but it really should be rare. For testing, you would probably want to use a setup with many devices that share the same airq area (you can fit a lot of devices if they have few queues), generate traffic on the queues, and then do something that triggers the callback (adding/removing a new device in a loop?) I currently don't have such a setup handy; Halil, would you be able to test that?> >> --- >> drivers/s390/virtio/virtio_ccw.c | 27 +++++++++++++++++++++++++++ >> 1 file changed, 27 insertions(+) >> >> diff --git a/drivers/s390/virtio/virtio_ccw.c b/drivers/s390/virtio/virtio_ccw.c >> index d35e7a3f7067..c19f07a82d62 100644 >> --- a/drivers/s390/virtio/virtio_ccw.c >> +++ b/drivers/s390/virtio/virtio_ccw.c >> @@ -62,6 +62,7 @@ struct virtio_ccw_device { >> unsigned int revision; /* Transport revision */ >> wait_queue_head_t wait_q; >> spinlock_t lock; >> + spinlock_t irq_lock; >> struct mutex io_lock; /* Serializes I/O requests */ >> struct list_head virtqueues; >> bool is_thinint; >> @@ -984,6 +985,27 @@ static const char *virtio_ccw_bus_name(struct virtio_device *vdev) >> return dev_name(&vcdev->cdev->dev); >> } >> >> +static void virtio_ccw_synchronize_cbs(struct virtio_device *vdev) >> +{ >> + struct virtio_ccw_device *vcdev = to_vc_device(vdev); >> + struct airq_info *info = vcdev->airq_info; >> + >> + /* >> + * Synchronize with the vring_interrupt() called by >> + * virtio_ccw_int_handler(). >> + */ >> + spin_lock(&vcdev->irq_lock); >> + spin_unlock(&vcdev->irq_lock); >> + >> + if (info) { >> + /* >> + * Synchronize with the vring_interrupt() with airq indicator >> + */ >> + write_lock(&info->lock); >> + write_unlock(&info->lock); >> + }I think we can make this an either/or operation (devices will either use classic interrupts or adapter interrupts)?>> +} >> + >> static const struct virtio_config_ops virtio_ccw_config_ops = { >> .get_features = virtio_ccw_get_features, >> .finalize_features = virtio_ccw_finalize_features,