This patch adds an operation callback which gets called every time the
library wants to call eventfd_write(). This eventfd_write() call could
result in a system call, which could potentially block the PMD thread.
The callback function can decide whether it's ok to handle the
eventfd_write() now or have the newly introduced function,
rte_vhost_notify_guest(), called at a later time.
This can be used by 3rd party applications, like OVS, to avoid system
calls being called as part of the PMD threads.
Signed-off-by: Eelco Chaudron <echau...@redhat.com>
---
lib/vhost/rte_vhost.h | 10 +++++++++-
lib/vhost/vhost.c | 21 +++++++++++++++++++++
lib/vhost/vhost.h | 43 ++++++++++++++++++++++++++++---------------
3 files changed, 58 insertions(+), 16 deletions(-)
diff --git a/lib/vhost/rte_vhost.h b/lib/vhost/rte_vhost.h
index 58a5d4be92..af7a394d0f 100644
--- a/lib/vhost/rte_vhost.h
+++ b/lib/vhost/rte_vhost.h
@@ -298,7 +298,13 @@ struct rte_vhost_device_ops {
*/
void (*guest_notified)(int vid);
- void *reserved[1]; /**< Reserved for future extension */
+ /**
+ * If this callback is registered, notification to the guest can
+ * be handled by the front-end calling rte_vhost_notify_guest().
+ * If it's not handled, 'false' should be returned. This can be used
+ * to remove the "slow" eventfd_write() syscall from the datapath.
+ */
+ bool (*guest_notify)(int vid, uint16_t queue_id);
};
/**
@@ -433,6 +439,8 @@ void rte_vhost_log_used_vring(int vid, uint16_t vring_idx,
int rte_vhost_enable_guest_notification(int vid, uint16_t queue_id, int
enable);
+void rte_vhost_notify_guest(int vid, uint16_t queue_id);
+
/**
* Register vhost driver. path could be different for multiple
* instance support.
diff --git a/lib/vhost/vhost.c b/lib/vhost/vhost.c
index ef37943817..ee090d78ef 100644
--- a/lib/vhost/vhost.c
+++ b/lib/vhost/vhost.c
@@ -1467,6 +1467,27 @@ rte_vhost_enable_guest_notification(int vid, uint16_t
queue_id, int enable)
return ret;
}
+void
+rte_vhost_notify_guest(int vid, uint16_t queue_id)
+{
+ struct virtio_net *dev = get_device(vid);
+ struct vhost_virtqueue *vq;
+
+ if (!dev || queue_id >= VHOST_MAX_VRING)
+ return;
+
+ vq = dev->virtqueue[queue_id];
+ if (!vq)
+ return;
+
+ rte_spinlock_lock(&vq->access_lock);
+
+ if (vq->callfd >= 0)
+ eventfd_write(vq->callfd, (eventfd_t)1);
+
+ rte_spinlock_unlock(&vq->access_lock);
+}
+
void
rte_vhost_log_write(int vid, uint64_t addr, uint64_t len)
{
diff --git a/lib/vhost/vhost.h b/lib/vhost/vhost.h
index 8fdab13c70..39ad8260a1 100644
--- a/lib/vhost/vhost.h
+++ b/lib/vhost/vhost.h
@@ -883,6 +883,30 @@ vhost_need_event(uint16_t event_idx, uint16_t new_idx,
uint16_t old)
return (uint16_t)(new_idx - event_idx - 1) < (uint16_t)(new_idx - old);
}
+static __rte_always_inline void
+vhost_vring_kick_guest(struct virtio_net *dev, struct vhost_virtqueue *vq)
+{
+ if (dev->notify_ops->guest_notify) {
+ uint16_t qid;
+ for (qid = 0; qid < dev->nr_vring; qid++) {
+ if (dev->virtqueue[qid] == vq) {
+ if (dev->notify_ops->guest_notify(dev->vid,
+ qid))
+ goto done;
+ break;
+ }
+ }
+ }
+ eventfd_write(vq->callfd, (eventfd_t) 1);
+
+done:
+ if (dev->flags & VIRTIO_DEV_STATS_ENABLED)
+ vq->stats.guest_notifications++;
+ if (dev->notify_ops->guest_notified)
+ dev->notify_ops->guest_notified(dev->vid);
+}
+
+
static __rte_always_inline void
vhost_vring_call_split(struct virtio_net *dev, struct vhost_virtqueue *vq)
{
@@ -905,21 +929,13 @@ vhost_vring_call_split(struct virtio_net *dev, struct
vhost_virtqueue *vq)
if ((vhost_need_event(vhost_used_event(vq), new, old) &&
(vq->callfd >= 0)) ||
unlikely(!signalled_used_valid)) {
- eventfd_write(vq->callfd, (eventfd_t) 1);
- if (dev->flags & VIRTIO_DEV_STATS_ENABLED)
- vq->stats.guest_notifications++;
- if (dev->notify_ops->guest_notified)
- dev->notify_ops->guest_notified(dev->vid);
+ vhost_vring_kick_guest(dev, vq);
}
} else {
/* Kick the guest if necessary. */
if (!(vq->avail->flags & VRING_AVAIL_F_NO_INTERRUPT)
&& (vq->callfd >= 0)) {
- eventfd_write(vq->callfd, (eventfd_t)1);
- if (dev->flags & VIRTIO_DEV_STATS_ENABLED)
- vq->stats.guest_notifications++;
- if (dev->notify_ops->guest_notified)
- dev->notify_ops->guest_notified(dev->vid);
+ vhost_vring_kick_guest(dev, vq);
}
}
}
@@ -971,11 +987,8 @@ vhost_vring_call_packed(struct virtio_net *dev, struct
vhost_virtqueue *vq)
if (vhost_need_event(off, new, old))
kick = true;
kick:
- if (kick) {
- eventfd_write(vq->callfd, (eventfd_t)1);
- if (dev->notify_ops->guest_notified)
- dev->notify_ops->guest_notified(dev->vid);
- }
+ if (kick)
+ vhost_vring_kick_guest(dev, vq);
}
static __rte_always_inline void
