[dpdk-dev] [PATCH 04/10] net/virtio: optimize flags update for packed ring

[Jens Freimann]

On Tue, Mar 19, 2019 at 02:43:06PM +0800, Tiwei Bie wrote:
>Cache the AVAIL, USED and WRITE bits to avoid calculating
>them as much as possible. Note that, the WRITE bit isn't
>cached for control queue.
>
>Signed-off-by: Tiwei Bie <tiwei.bie at intel.com>
>---
> drivers/net/virtio/virtio_ethdev.c | 35 ++++++++++++++----------------
> drivers/net/virtio/virtio_rxtx.c   | 31 ++++++++++----------------
> drivers/net/virtio/virtqueue.h     |  8 +++----
> 3 files changed, 32 insertions(+), 42 deletions(-)
>
>diff --git a/drivers/net/virtio/virtio_ethdev.c b/drivers/net/virtio/virtio_ethdev.c
>index ff16fb63e..9060b6b33 100644
>--- a/drivers/net/virtio/virtio_ethdev.c
>+++ b/drivers/net/virtio/virtio_ethdev.c
>@@ -149,7 +149,7 @@ virtio_send_command_packed(struct virtnet_ctl *cvq,
> 	int head;
> 	struct vring_packed_desc *desc = vq->ring_packed.desc_packed;
> 	struct virtio_pmd_ctrl *result;
>-	bool avail_wrap_counter;
>+	uint16_t flags;
> 	int sum = 0;
> 	int nb_descs = 0;
> 	int k;
>@@ -161,14 +161,15 @@ virtio_send_command_packed(struct virtnet_ctl *cvq,
> 	 * One RX packet for ACK.
> 	 */
> 	head = vq->vq_avail_idx;
>-	avail_wrap_counter = vq->avail_wrap_counter;
>+	flags = vq->cached_flags;
> 	desc[head].addr = cvq->virtio_net_hdr_mem;
> 	desc[head].len = sizeof(struct virtio_net_ctrl_hdr);
> 	vq->vq_free_cnt--;
> 	nb_descs++;
> 	if (++vq->vq_avail_idx >= vq->vq_nentries) {
> 		vq->vq_avail_idx -= vq->vq_nentries;
>-		vq->avail_wrap_counter ^= 1;
>+		vq->cached_flags ^=
>+			VRING_DESC_F_AVAIL(1) | VRING_DESC_F_USED(1);

Maybe name it avail_used_flags instead of cached flags. Also we could
use a constant value. 

> 	}
>
> 	for (k = 0; k < pkt_num; k++) {
>@@ -177,34 +178,31 @@ virtio_send_command_packed(struct virtnet_ctl *cvq,
> 			+ sizeof(ctrl->status) + sizeof(uint8_t) * sum;
> 		desc[vq->vq_avail_idx].len = dlen[k];
> 		desc[vq->vq_avail_idx].flags = VRING_DESC_F_NEXT |
>-			VRING_DESC_F_AVAIL(vq->avail_wrap_counter) |
>-			VRING_DESC_F_USED(!vq->avail_wrap_counter);
>+			vq->cached_flags;
> 		sum += dlen[k];
> 		vq->vq_free_cnt--;
> 		nb_descs++;
> 		if (++vq->vq_avail_idx >= vq->vq_nentries) {
> 			vq->vq_avail_idx -= vq->vq_nentries;
>-			vq->avail_wrap_counter ^= 1;
>+			vq->cached_flags ^=
>+				VRING_DESC_F_AVAIL(1) | VRING_DESC_F_USED(1);
> 		}
> 	}
>
> 	desc[vq->vq_avail_idx].addr = cvq->virtio_net_hdr_mem
> 		+ sizeof(struct virtio_net_ctrl_hdr);
> 	desc[vq->vq_avail_idx].len = sizeof(ctrl->status);
>-	desc[vq->vq_avail_idx].flags = VRING_DESC_F_WRITE |
>-		VRING_DESC_F_AVAIL(vq->avail_wrap_counter) |
>-		VRING_DESC_F_USED(!vq->avail_wrap_counter);
>+	desc[vq->vq_avail_idx].flags = VRING_DESC_F_WRITE | vq->cached_flags;
> 	vq->vq_free_cnt--;
> 	nb_descs++;
> 	if (++vq->vq_avail_idx >= vq->vq_nentries) {
> 		vq->vq_avail_idx -= vq->vq_nentries;
>-		vq->avail_wrap_counter ^= 1;
>+		vq->cached_flags ^=
>+			VRING_DESC_F_AVAIL(1) | VRING_DESC_F_USED(1);
> 	}
>
> 	virtio_wmb(vq->hw->weak_barriers);
>-	desc[head].flags = VRING_DESC_F_NEXT |
>-		VRING_DESC_F_AVAIL(avail_wrap_counter) |
>-		VRING_DESC_F_USED(!avail_wrap_counter);
>+	desc[head].flags = VRING_DESC_F_NEXT | flags;
>
> 	virtio_wmb(vq->hw->weak_barriers);
> 	virtqueue_notify(vq);
>@@ -226,12 +224,12 @@ virtio_send_command_packed(struct virtnet_ctl *cvq,
> 	PMD_INIT_LOG(DEBUG, "vq->vq_free_cnt=%d\n"
> 			"vq->vq_avail_idx=%d\n"
> 			"vq->vq_used_cons_idx=%d\n"
>-			"vq->avail_wrap_counter=%d\n"
>+			"vq->cached_flags=0x%x\n"
> 			"vq->used_wrap_counter=%d\n",
> 			vq->vq_free_cnt,
> 			vq->vq_avail_idx,
> 			vq->vq_used_cons_idx,
>-			vq->avail_wrap_counter,
>+			vq->cached_flags,
> 			vq->used_wrap_counter);
>
> 	result = cvq->virtio_net_hdr_mz->addr;
>@@ -491,11 +489,10 @@ virtio_init_queue(struct rte_eth_dev *dev, uint16_t vtpci_queue_idx)
> 	vq->vq_nentries = vq_size;
> 	vq->event_flags_shadow = 0;
> 	if (vtpci_packed_queue(hw)) {
>-		vq->avail_wrap_counter = 1;
> 		vq->used_wrap_counter = 1;
>-		vq->avail_used_flags =
>-			VRING_DESC_F_AVAIL(vq->avail_wrap_counter) |
>-			VRING_DESC_F_USED(!vq->avail_wrap_counter);
>+		vq->cached_flags = VRING_DESC_F_AVAIL(1);
>+		if (queue_type == VTNET_RQ)
>+			vq->cached_flags |= VRING_DESC_F_WRITE;
> 	}
>
> 	/*
>diff --git a/drivers/net/virtio/virtio_rxtx.c b/drivers/net/virtio/virtio_rxtx.c
>index 771d3c3f6..3c354baef 100644
>--- a/drivers/net/virtio/virtio_rxtx.c
>+++ b/drivers/net/virtio/virtio_rxtx.c
>@@ -431,7 +431,7 @@ virtqueue_enqueue_recv_refill_packed(struct virtqueue *vq,
> 				     struct rte_mbuf **cookie, uint16_t num)
> {
> 	struct vring_packed_desc *start_dp = vq->ring_packed.desc_packed;
>-	uint16_t flags = VRING_DESC_F_WRITE | vq->avail_used_flags;
>+	uint16_t flags = vq->cached_flags;
> 	struct virtio_hw *hw = vq->hw;
> 	struct vq_desc_extra *dxp;
> 	uint16_t idx;
>@@ -460,11 +460,9 @@ virtqueue_enqueue_recv_refill_packed(struct virtqueue *vq,
> 		start_dp[idx].flags = flags;
> 		if (++vq->vq_avail_idx >= vq->vq_nentries) {
> 			vq->vq_avail_idx -= vq->vq_nentries;
>-			vq->avail_wrap_counter ^= 1;
>-			vq->avail_used_flags =
>-				VRING_DESC_F_AVAIL(vq->avail_wrap_counter) |
>-				VRING_DESC_F_USED(!vq->avail_wrap_counter);
>-			flags = VRING_DESC_F_WRITE | vq->avail_used_flags;
>+			vq->cached_flags ^=
>+				VRING_DESC_F_AVAIL(1) | VRING_DESC_F_USED(1);
>+			flags = vq->cached_flags;

same here. it's not really cached, it's pre-calculated. And here we
could also use a pre-calculated constand/define. 

Otherwise looks good! Did you see any performance improvements?


regards,
Jens