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virtio_ring: leverage event idx in packed ring

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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>
This commit is contained in:
Tiwei Bie 2018-11-21 18:03:28 +08:00 committed by David S. Miller
parent 1ce9e6055f
commit f51f982682
1 changed files with 71 additions and 6 deletions
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77
drivers/virtio/virtio_ring.c
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@ -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);
}