Revert "vhost: cache used event for better performance"

BugLink: http://bugs.launchpad.net/bugs/1711251
commit 8d65843c44269c21e95c98090d9bb4848d473853 upstream

This reverts commit 809ecb9bca6a9424ccd392d67e368160f8b76c92.

Signed-off-by: Joseph Salisbury <joseph.salisbury@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Colin King <colin.king@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 8f99fe08de02e7b48725a99d682055c03056b82a..8d05a40e5ae2caa0f3be6e4ed391c9f799e443b0 100644 (file)
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -290,7 +290,6 @@ static void vhost_vq_reset(struct vhost_dev *dev,
        vq->avail = NULL;
        vq->used = NULL;
        vq->last_avail_idx = 0;
-       vq->last_used_event = 0;
        vq->avail_idx = 0;
        vq->last_used_idx = 0;
        vq->signalled_used = 0;
@@ -1325,7 +1324,7 @@ long vhost_vring_ioctl(struct vhost_dev *d, int ioctl, void __user *argp)
                        r = -EINVAL;
                        break;
                }
-               vq->last_avail_idx = vq->last_used_event = s.num;
+               vq->last_avail_idx = s.num;
                /* Forget the cached index value. */
                vq->avail_idx = vq->last_avail_idx;
                break;
@@ -2157,6 +2156,10 @@ static bool vhost_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
        __u16 old, new;
        __virtio16 event;
        bool v;
+       /* Flush out used index updates. This is paired
+        * with the barrier that the Guest executes when enabling
+        * interrupts. */
+       smp_mb();
 
        if (vhost_has_feature(vq, VIRTIO_F_NOTIFY_ON_EMPTY) &&
            unlikely(vq->avail_idx == vq->last_avail_idx))
@@ -2164,10 +2167,6 @@ static bool vhost_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
 
        if (!vhost_has_feature(vq, VIRTIO_RING_F_EVENT_IDX)) {
                __virtio16 flags;
-               /* Flush out used index updates. This is paired
-                * with the barrier that the Guest executes when enabling
-                * interrupts. */
-               smp_mb();
                if (vhost_get_user(vq, flags, &vq->avail->flags)) {
                        vq_err(vq, "Failed to get flags");
                        return true;
@@ -2182,26 +2181,11 @@ static bool vhost_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
        if (unlikely(!v))
                return true;
 
-       /* We're sure if the following conditions are met, there's no
-        * need to notify guest:
-        * 1) cached used event is ahead of new
-        * 2) old to new updating does not cross cached used event. */
-       if (vring_need_event(vq->last_used_event, new + vq->num, new) &&
-           !vring_need_event(vq->last_used_event, new, old))
-               return false;
-
-       /* Flush out used index updates. This is paired
-        * with the barrier that the Guest executes when enabling
-        * interrupts. */
-       smp_mb();
-
        if (vhost_get_user(vq, event, vhost_used_event(vq))) {
                vq_err(vq, "Failed to get used event idx");
                return true;
        }
-       vq->last_used_event = vhost16_to_cpu(vq, event);
-
-       return vring_need_event(vq->last_used_event, new, old);
+       return vring_need_event(vhost16_to_cpu(vq, event), new, old);
 }
 
 /* This actually signals the guest, using eventfd. */

diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index a9cbbb148f460e52ef8a051770fd32f616696f14..78f3c5fc02e47d92bced439249a4bb3491e42e9a 100644 (file)
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -107,9 +107,6 @@ struct vhost_virtqueue {
        /* Last index we used. */
        u16 last_used_idx;
 
-       /* Last used evet we've seen */
-       u16 last_used_event;
-
        /* Used flags */
        u16 used_flags;