virtio_ring: leverage event idx in packed ring

Leverage the EVENT_IDX feature in packed ring to suppress
events when it's available.

Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index b63eee2..40e4d37 100644 (file)
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -1222,7 +1222,7 @@ unmap_release:
 static bool virtqueue_kick_prepare_packed(struct virtqueue *_vq)
 {
        struct vring_virtqueue *vq = to_vvq(_vq);
-       u16 flags;
+       u16 new, old, off_wrap, flags, wrap_counter, event_idx;
        bool needs_kick;
        union {
                struct {
@@ -1240,6 +1240,8 @@ static bool virtqueue_kick_prepare_packed(struct virtqueue *_vq)
         */
        virtio_mb(vq->weak_barriers);
 
+       old = vq->packed.next_avail_idx - vq->num_added;
+       new = vq->packed.next_avail_idx;
        vq->num_added = 0;
 
        snapshot.u32 = *(u32 *)vq->packed.vring.device;
@@ -1248,7 +1250,20 @@ static bool virtqueue_kick_prepare_packed(struct virtqueue *_vq)
        LAST_ADD_TIME_CHECK(vq);
        LAST_ADD_TIME_INVALID(vq);
 
-       needs_kick = (flags != VRING_PACKED_EVENT_FLAG_DISABLE);
+       if (flags != VRING_PACKED_EVENT_FLAG_DESC) {
+               needs_kick = (flags != VRING_PACKED_EVENT_FLAG_DISABLE);
+               goto out;
+       }
+
+       off_wrap = le16_to_cpu(snapshot.off_wrap);
+
+       wrap_counter = off_wrap >> VRING_PACKED_EVENT_F_WRAP_CTR;
+       event_idx = off_wrap & ~(1 << VRING_PACKED_EVENT_F_WRAP_CTR);
+       if (wrap_counter != vq->packed.avail_wrap_counter)
+               event_idx -= vq->packed.vring.num;
+
+       needs_kick = vring_need_event(event_idx, new, old);
+out:
        END_USE(vq);
        return needs_kick;
 }
@@ -1365,6 +1380,18 @@ static void *virtqueue_get_buf_ctx_packed(struct virtqueue *_vq,
                vq->packed.used_wrap_counter ^= 1;
        }
 
+       /*
+        * If we expect an interrupt for the next entry, tell host
+        * by writing event index and flush out the write before
+        * the read in the next get_buf call.
+        */
+       if (vq->packed.event_flags_shadow == VRING_PACKED_EVENT_FLAG_DESC)
+               virtio_store_mb(vq->weak_barriers,
+                               &vq->packed.vring.driver->off_wrap,
+                               cpu_to_le16(vq->last_used_idx |
+                                       (vq->packed.used_wrap_counter <<
+                                        VRING_PACKED_EVENT_F_WRAP_CTR)));
+
        LAST_ADD_TIME_INVALID(vq);
 
        END_USE(vq);
@@ -1393,8 +1420,22 @@ static unsigned virtqueue_enable_cb_prepare_packed(struct virtqueue *_vq)
         * more to do.
         */
 
+       if (vq->event) {
+               vq->packed.vring.driver->off_wrap =
+                       cpu_to_le16(vq->last_used_idx |
+                               (vq->packed.used_wrap_counter <<
+                                VRING_PACKED_EVENT_F_WRAP_CTR));
+               /*
+                * We need to update event offset and event wrap
+                * counter first before updating event flags.
+                */
+               virtio_wmb(vq->weak_barriers);
+       }
+
        if (vq->packed.event_flags_shadow == VRING_PACKED_EVENT_FLAG_DISABLE) {
-               vq->packed.event_flags_shadow = VRING_PACKED_EVENT_FLAG_ENABLE;
+               vq->packed.event_flags_shadow = vq->event ?
+                               VRING_PACKED_EVENT_FLAG_DESC :
+                               VRING_PACKED_EVENT_FLAG_ENABLE;
                vq->packed.vring.driver->flags =
                                cpu_to_le16(vq->packed.event_flags_shadow);
        }
@@ -1420,6 +1461,7 @@ static bool virtqueue_enable_cb_delayed_packed(struct virtqueue *_vq)
 {
        struct vring_virtqueue *vq = to_vvq(_vq);
        u16 used_idx, wrap_counter;
+       u16 bufs;
 
        START_USE(vq);
 
@@ -1428,11 +1470,34 @@ static bool virtqueue_enable_cb_delayed_packed(struct virtqueue *_vq)
         * more to do.
         */
 
-       used_idx = vq->last_used_idx;
-       wrap_counter = vq->packed.used_wrap_counter;
+       if (vq->event) {
+               /* TODO: tune this threshold */
+               bufs = (vq->packed.vring.num - vq->vq.num_free) * 3 / 4;
+               wrap_counter = vq->packed.used_wrap_counter;
+
+               used_idx = vq->last_used_idx + bufs;
+               if (used_idx >= vq->packed.vring.num) {
+                       used_idx -= vq->packed.vring.num;
+                       wrap_counter ^= 1;
+               }
+
+               vq->packed.vring.driver->off_wrap = cpu_to_le16(used_idx |
+                       (wrap_counter << VRING_PACKED_EVENT_F_WRAP_CTR));
+
+               /*
+                * We need to update event offset and event wrap
+                * counter first before updating event flags.
+                */
+               virtio_wmb(vq->weak_barriers);
+       } else {
+               used_idx = vq->last_used_idx;
+               wrap_counter = vq->packed.used_wrap_counter;
+       }
 
        if (vq->packed.event_flags_shadow == VRING_PACKED_EVENT_FLAG_DISABLE) {
-               vq->packed.event_flags_shadow = VRING_PACKED_EVENT_FLAG_ENABLE;
+               vq->packed.event_flags_shadow = vq->event ?
+                               VRING_PACKED_EVENT_FLAG_DESC :
+                               VRING_PACKED_EVENT_FLAG_ENABLE;
                vq->packed.vring.driver->flags =
                                cpu_to_le16(vq->packed.event_flags_shadow);
        }