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

[Tiwei Bie]

On Tue, Mar 19, 2019 at 09:54:03AM +0100, Jens Freimann wrote:
> 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.

It also contains the WRITE bit (not just AVAIL and USED bits)
for Rx path. That's why I didn't name it as avail_used_flags.

> 
> > 	}
> > 
> > 	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.

For pre-calculated constant/define, do you mean VRING_DESC_F_AVAIL(1)
and VRING_DESC_F_USED(1)? There is still little code in virtio-user
using them without constantly passing 1. I planned to fully get rid
of them in a separate patch later (but I can do it in this series if
anyone wants).

> 
> Otherwise looks good! Did you see any performance improvements?

Yeah, I saw slightly better performance in a quick test.

Thanks,
Tiwei

> 
> 
> regards,
> Jens