vhost: support event index
Michael S. Tsirkin [Thu, 19 May 2011 23:10:54 +0000 (02:10 +0300)]
Support the new event index feature. When acked,
utilize it to reduce the # of interrupts sent to the guest.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

drivers/vhost/net.c
drivers/vhost/test.c
drivers/vhost/vhost.c
drivers/vhost/vhost.h

index 2f7c76a..e224a92 100644 (file)
@@ -144,7 +144,7 @@ static void handle_tx(struct vhost_net *net)
        }
 
        mutex_lock(&vq->mutex);
-       vhost_disable_notify(vq);
+       vhost_disable_notify(&net->dev, vq);
 
        if (wmem < sock->sk->sk_sndbuf / 2)
                tx_poll_stop(net);
@@ -166,8 +166,8 @@ static void handle_tx(struct vhost_net *net)
                                set_bit(SOCK_ASYNC_NOSPACE, &sock->flags);
                                break;
                        }
-                       if (unlikely(vhost_enable_notify(vq))) {
-                               vhost_disable_notify(vq);
+                       if (unlikely(vhost_enable_notify(&net->dev, vq))) {
+                               vhost_disable_notify(&net->dev, vq);
                                continue;
                        }
                        break;
@@ -315,7 +315,7 @@ static void handle_rx(struct vhost_net *net)
                return;
 
        mutex_lock(&vq->mutex);
-       vhost_disable_notify(vq);
+       vhost_disable_notify(&net->dev, vq);
        vhost_hlen = vq->vhost_hlen;
        sock_hlen = vq->sock_hlen;
 
@@ -334,10 +334,10 @@ static void handle_rx(struct vhost_net *net)
                        break;
                /* OK, now we need to know about added descriptors. */
                if (!headcount) {
-                       if (unlikely(vhost_enable_notify(vq))) {
+                       if (unlikely(vhost_enable_notify(&net->dev, vq))) {
                                /* They have slipped one in as we were
                                 * doing that: check again. */
-                               vhost_disable_notify(vq);
+                               vhost_disable_notify(&net->dev, vq);
                                continue;
                        }
                        /* Nothing new?  Wait for eventfd to tell us
index 099f302..734e1d7 100644 (file)
@@ -49,7 +49,7 @@ static void handle_vq(struct vhost_test *n)
                return;
 
        mutex_lock(&vq->mutex);
-       vhost_disable_notify(vq);
+       vhost_disable_notify(&n->dev, vq);
 
        for (;;) {
                head = vhost_get_vq_desc(&n->dev, vq, vq->iov,
@@ -61,8 +61,8 @@ static void handle_vq(struct vhost_test *n)
                        break;
                /* Nothing new?  Wait for eventfd to tell us they refilled. */
                if (head == vq->num) {
-                       if (unlikely(vhost_enable_notify(vq))) {
-                               vhost_disable_notify(vq);
+                       if (unlikely(vhost_enable_notify(&n->dev, vq))) {
+                               vhost_disable_notify(&n->dev, vq);
                                continue;
                        }
                        break;
index 7aa4eea..ea966b3 100644 (file)
@@ -37,6 +37,9 @@ enum {
        VHOST_MEMORY_F_LOG = 0x1,
 };
 
+#define vhost_used_event(vq) ((u16 __user *)&vq->avail->ring[vq->num])
+#define vhost_avail_event(vq) ((u16 __user *)&vq->used->ring[vq->num])
+
 static void vhost_poll_func(struct file *file, wait_queue_head_t *wqh,
                            poll_table *pt)
 {
@@ -161,6 +164,8 @@ static void vhost_vq_reset(struct vhost_dev *dev,
        vq->last_avail_idx = 0;
        vq->avail_idx = 0;
        vq->last_used_idx = 0;
+       vq->signalled_used = 0;
+       vq->signalled_used_valid = false;
        vq->used_flags = 0;
        vq->log_used = false;
        vq->log_addr = -1ull;
@@ -489,16 +494,17 @@ static int memory_access_ok(struct vhost_dev *d, struct vhost_memory *mem,
        return 1;
 }
 
-static int vq_access_ok(unsigned int num,
+static int vq_access_ok(struct vhost_dev *d, unsigned int num,
                        struct vring_desc __user *desc,
                        struct vring_avail __user *avail,
                        struct vring_used __user *used)
 {
+       size_t s = vhost_has_feature(d, VIRTIO_RING_F_EVENT_IDX) ? 2 : 0;
        return access_ok(VERIFY_READ, desc, num * sizeof *desc) &&
               access_ok(VERIFY_READ, avail,
-                        sizeof *avail + num * sizeof *avail->ring) &&
+                        sizeof *avail + num * sizeof *avail->ring + s) &&
               access_ok(VERIFY_WRITE, used,
-                       sizeof *used + num * sizeof *used->ring);
+                       sizeof *used + num * sizeof *used->ring + s);
 }
 
 /* Can we log writes? */
@@ -514,9 +520,11 @@ int vhost_log_access_ok(struct vhost_dev *dev)
 
 /* Verify access for write logging. */
 /* Caller should have vq mutex and device mutex */
-static int vq_log_access_ok(struct vhost_virtqueue *vq, void __user *log_base)
+static int vq_log_access_ok(struct vhost_dev *d, struct vhost_virtqueue *vq,
+                           void __user *log_base)
 {
        struct vhost_memory *mp;
+       size_t s = vhost_has_feature(d, VIRTIO_RING_F_EVENT_IDX) ? 2 : 0;
 
        mp = rcu_dereference_protected(vq->dev->memory,
                                       lockdep_is_held(&vq->mutex));
@@ -524,15 +532,15 @@ static int vq_log_access_ok(struct vhost_virtqueue *vq, void __user *log_base)
                            vhost_has_feature(vq->dev, VHOST_F_LOG_ALL)) &&
                (!vq->log_used || log_access_ok(log_base, vq->log_addr,
                                        sizeof *vq->used +
-                                       vq->num * sizeof *vq->used->ring));
+                                       vq->num * sizeof *vq->used->ring + s));
 }
 
 /* Can we start vq? */
 /* Caller should have vq mutex and device mutex */
 int vhost_vq_access_ok(struct vhost_virtqueue *vq)
 {
-       return vq_access_ok(vq->num, vq->desc, vq->avail, vq->used) &&
-               vq_log_access_ok(vq, vq->log_base);
+       return vq_access_ok(vq->dev, vq->num, vq->desc, vq->avail, vq->used) &&
+               vq_log_access_ok(vq->dev, vq, vq->log_base);
 }
 
 static long vhost_set_memory(struct vhost_dev *d, struct vhost_memory __user *m)
@@ -577,6 +585,7 @@ static int init_used(struct vhost_virtqueue *vq,
 
        if (r)
                return r;
+       vq->signalled_used_valid = false;
        return get_user(vq->last_used_idx, &used->idx);
 }
 
@@ -674,7 +683,7 @@ static long vhost_set_vring(struct vhost_dev *d, int ioctl, void __user *argp)
                 * If it is not, we don't as size might not have been setup.
                 * We will verify when backend is configured. */
                if (vq->private_data) {
-                       if (!vq_access_ok(vq->num,
+                       if (!vq_access_ok(d, vq->num,
                                (void __user *)(unsigned long)a.desc_user_addr,
                                (void __user *)(unsigned long)a.avail_user_addr,
                                (void __user *)(unsigned long)a.used_user_addr)) {
@@ -818,7 +827,7 @@ long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, unsigned long arg)
                        vq = d->vqs + i;
                        mutex_lock(&vq->mutex);
                        /* If ring is inactive, will check when it's enabled. */
-                       if (vq->private_data && !vq_log_access_ok(vq, base))
+                       if (vq->private_data && !vq_log_access_ok(d, vq, base))
                                r = -EFAULT;
                        else
                                vq->log_base = base;
@@ -1219,6 +1228,10 @@ int vhost_get_vq_desc(struct vhost_dev *dev, struct vhost_virtqueue *vq,
 
        /* On success, increment avail index. */
        vq->last_avail_idx++;
+
+       /* Assume notifications from guest are disabled at this point,
+        * if they aren't we would need to update avail_event index. */
+       BUG_ON(!(vq->used_flags & VRING_USED_F_NO_NOTIFY));
        return head;
 }
 
@@ -1267,6 +1280,12 @@ int vhost_add_used(struct vhost_virtqueue *vq, unsigned int head, int len)
                        eventfd_signal(vq->log_ctx, 1);
        }
        vq->last_used_idx++;
+       /* If the driver never bothers to signal in a very long while,
+        * used index might wrap around. If that happens, invalidate
+        * signalled_used index we stored. TODO: make sure driver
+        * signals at least once in 2^16 and remove this. */
+       if (unlikely(vq->last_used_idx == vq->signalled_used))
+               vq->signalled_used_valid = false;
        return 0;
 }
 
@@ -1275,6 +1294,7 @@ static int __vhost_add_used_n(struct vhost_virtqueue *vq,
                            unsigned count)
 {
        struct vring_used_elem __user *used;
+       u16 old, new;
        int start;
 
        start = vq->last_used_idx % vq->num;
@@ -1292,7 +1312,14 @@ static int __vhost_add_used_n(struct vhost_virtqueue *vq,
                           ((void __user *)used - (void __user *)vq->used),
                          count * sizeof *used);
        }
-       vq->last_used_idx += count;
+       old = vq->last_used_idx;
+       new = (vq->last_used_idx += count);
+       /* If the driver never bothers to signal in a very long while,
+        * used index might wrap around. If that happens, invalidate
+        * signalled_used index we stored. TODO: make sure driver
+        * signals at least once in 2^16 and remove this. */
+       if (unlikely((u16)(new - vq->signalled_used) < (u16)(new - old)))
+               vq->signalled_used_valid = false;
        return 0;
 }
 
@@ -1331,29 +1358,47 @@ int vhost_add_used_n(struct vhost_virtqueue *vq, struct vring_used_elem *heads,
        return r;
 }
 
-/* This actually signals the guest, using eventfd. */
-void vhost_signal(struct vhost_dev *dev, struct vhost_virtqueue *vq)
+static bool vhost_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
 {
-       __u16 flags;
-
+       __u16 old, new, event;
+       bool v;
        /* Flush out used index updates. This is paired
         * with the barrier that the Guest executes when enabling
         * interrupts. */
        smp_mb();
 
-       if (__get_user(flags, &vq->avail->flags)) {
-               vq_err(vq, "Failed to get flags");
-               return;
+       if (vhost_has_feature(dev, VIRTIO_F_NOTIFY_ON_EMPTY) &&
+           unlikely(vq->avail_idx == vq->last_avail_idx))
+               return true;
+
+       if (!vhost_has_feature(dev, VIRTIO_RING_F_EVENT_IDX)) {
+               __u16 flags;
+               if (__get_user(flags, &vq->avail->flags)) {
+                       vq_err(vq, "Failed to get flags");
+                       return true;
+               }
+               return !(flags & VRING_AVAIL_F_NO_INTERRUPT);
        }
+       old = vq->signalled_used;
+       v = vq->signalled_used_valid;
+       new = vq->signalled_used = vq->last_used_idx;
+       vq->signalled_used_valid = true;
 
-       /* If they don't want an interrupt, don't signal, unless empty. */
-       if ((flags & VRING_AVAIL_F_NO_INTERRUPT) &&
-           (vq->avail_idx != vq->last_avail_idx ||
-            !vhost_has_feature(dev, VIRTIO_F_NOTIFY_ON_EMPTY)))
-               return;
+       if (unlikely(!v))
+               return true;
 
+       if (get_user(event, vhost_used_event(vq))) {
+               vq_err(vq, "Failed to get used event idx");
+               return true;
+       }
+       return vring_need_event(event, new, old);
+}
+
+/* This actually signals the guest, using eventfd. */
+void vhost_signal(struct vhost_dev *dev, struct vhost_virtqueue *vq)
+{
        /* Signal the Guest tell them we used something up. */
-       if (vq->call_ctx)
+       if (vq->call_ctx && vhost_notify(dev, vq))
                eventfd_signal(vq->call_ctx, 1);
 }
 
@@ -1376,7 +1421,7 @@ void vhost_add_used_and_signal_n(struct vhost_dev *dev,
 }
 
 /* OK, now we need to know about added descriptors. */
-bool vhost_enable_notify(struct vhost_virtqueue *vq)
+bool vhost_enable_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
 {
        u16 avail_idx;
        int r;
@@ -1384,11 +1429,34 @@ bool vhost_enable_notify(struct vhost_virtqueue *vq)
        if (!(vq->used_flags & VRING_USED_F_NO_NOTIFY))
                return false;
        vq->used_flags &= ~VRING_USED_F_NO_NOTIFY;
-       r = put_user(vq->used_flags, &vq->used->flags);
-       if (r) {
-               vq_err(vq, "Failed to enable notification at %p: %d\n",
-                      &vq->used->flags, r);
-               return false;
+       if (!vhost_has_feature(dev, VIRTIO_RING_F_EVENT_IDX)) {
+               r = put_user(vq->used_flags, &vq->used->flags);
+               if (r) {
+                       vq_err(vq, "Failed to enable notification at %p: %d\n",
+                              &vq->used->flags, r);
+                       return false;
+               }
+       } else {
+               r = put_user(vq->avail_idx, vhost_avail_event(vq));
+               if (r) {
+                       vq_err(vq, "Failed to update avail event index at %p: %d\n",
+                              vhost_avail_event(vq), r);
+                       return false;
+               }
+       }
+       if (unlikely(vq->log_used)) {
+               void __user *used;
+               /* Make sure data is seen before log. */
+               smp_wmb();
+               used = vhost_has_feature(dev, VIRTIO_RING_F_EVENT_IDX) ?
+                       &vq->used->flags : vhost_avail_event(vq);
+               /* Log used flags or event index entry write. Both are 16 bit
+                * fields. */
+               log_write(vq->log_base, vq->log_addr +
+                          (used - (void __user *)vq->used),
+                         sizeof(u16));
+               if (vq->log_ctx)
+                       eventfd_signal(vq->log_ctx, 1);
        }
        /* They could have slipped one in as we were doing that: make
         * sure it's written, then check again. */
@@ -1404,15 +1472,17 @@ bool vhost_enable_notify(struct vhost_virtqueue *vq)
 }
 
 /* We don't need to be notified again. */
-void vhost_disable_notify(struct vhost_virtqueue *vq)
+void vhost_disable_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
 {
        int r;
 
        if (vq->used_flags & VRING_USED_F_NO_NOTIFY)
                return;
        vq->used_flags |= VRING_USED_F_NO_NOTIFY;
-       r = put_user(vq->used_flags, &vq->used->flags);
-       if (r)
-               vq_err(vq, "Failed to enable notification at %p: %d\n",
-                      &vq->used->flags, r);
+       if (!vhost_has_feature(dev, VIRTIO_RING_F_EVENT_IDX)) {
+               r = put_user(vq->used_flags, &vq->used->flags);
+               if (r)
+                       vq_err(vq, "Failed to enable notification at %p: %d\n",
+                              &vq->used->flags, r);
+       }
 }
index b3363ae..8e03379 100644 (file)
@@ -84,6 +84,12 @@ struct vhost_virtqueue {
        /* Used flags */
        u16 used_flags;
 
+       /* Last used index value we have signalled on */
+       u16 signalled_used;
+
+       /* Last used index value we have signalled on */
+       bool signalled_used_valid;
+
        /* Log writes to used structure. */
        bool log_used;
        u64 log_addr;
@@ -149,8 +155,8 @@ void vhost_add_used_and_signal(struct vhost_dev *, struct vhost_virtqueue *,
 void vhost_add_used_and_signal_n(struct vhost_dev *, struct vhost_virtqueue *,
                               struct vring_used_elem *heads, unsigned count);
 void vhost_signal(struct vhost_dev *, struct vhost_virtqueue *);
-void vhost_disable_notify(struct vhost_virtqueue *);
-bool vhost_enable_notify(struct vhost_virtqueue *);
+void vhost_disable_notify(struct vhost_dev *, struct vhost_virtqueue *);
+bool vhost_enable_notify(struct vhost_dev *, struct vhost_virtqueue *);
 
 int vhost_log_write(struct vhost_virtqueue *vq, struct vhost_log *log,
                    unsigned int log_num, u64 len);
@@ -162,11 +168,12 @@ int vhost_log_write(struct vhost_virtqueue *vq, struct vhost_log *log,
        } while (0)
 
 enum {
-       VHOST_FEATURES = (1 << VIRTIO_F_NOTIFY_ON_EMPTY) |
-                        (1 << VIRTIO_RING_F_INDIRECT_DESC) |
-                        (1 << VHOST_F_LOG_ALL) |
-                        (1 << VHOST_NET_F_VIRTIO_NET_HDR) |
-                        (1 << VIRTIO_NET_F_MRG_RXBUF),
+       VHOST_FEATURES = (1ULL << VIRTIO_F_NOTIFY_ON_EMPTY) |
+                        (1ULL << VIRTIO_RING_F_INDIRECT_DESC) |
+                        (1ULL << VIRTIO_RING_F_EVENT_IDX) |
+                        (1ULL << VHOST_F_LOG_ALL) |
+                        (1ULL << VHOST_NET_F_VIRTIO_NET_HDR) |
+                        (1ULL << VIRTIO_NET_F_MRG_RXBUF),
 };
 
 static inline int vhost_has_feature(struct vhost_dev *dev, int bit)