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Subject[PATCH net-next v3 11/13] virtio_ring: leverage event idx in packed ring
Date
Leverage the EVENT_IDX feature in packed ring to suppress
events when it's available.

Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>
---
drivers/virtio/virtio_ring.c | 77 ++++++++++++++++++++++++++++++++++++++++----
1 file changed, 71 insertions(+), 6 deletions(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index b63eee2034e7..40e4d3798d16 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -1222,7 +1222,7 @@ static inline int virtqueue_add_packed(struct virtqueue *_vq,
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);
}
--
2.14.5
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