Re: [dpdk-dev] [PATCH v10 6/9] net/virtio: add vectorized packed ring Rx path

["Liu, Yong" <yong.liu@intel.com>]

> -----Original Message-----
> From: Maxime Coquelin <maxime.coquelin@redhat.com>
> Sent: Monday, April 27, 2020 7:21 PM
> To: Liu, Yong <yong.liu@intel.com>; Ye, Xiaolong <xiaolong.ye@intel.com>;
> Wang, Zhihong <zhihong.wang@intel.com>
> Cc: dev@dpdk.org
> Subject: Re: [PATCH v10 6/9] net/virtio: add vectorized packed ring Rx path
> 
> 
> 
> On 4/26/20 4:19 AM, Marvin Liu wrote:
> > Optimize packed ring Rx path with SIMD instructions. Solution of
> > optimization is pretty like vhost, is that split path into batch and
> > single functions. Batch function is further optimized by AVX512
> > instructions. Also pad desc extra structure to 16 bytes aligned, thus
> > four elements will be saved in one batch.
> >
> > Signed-off-by: Marvin Liu <yong.liu@intel.com>
> >
> > diff --git a/drivers/net/virtio/Makefile b/drivers/net/virtio/Makefile
> > index c9edb84ee..102b1deab 100644
> > --- a/drivers/net/virtio/Makefile
> > +++ b/drivers/net/virtio/Makefile
> > @@ -36,6 +36,41 @@ else ifneq ($(filter y,$(CONFIG_RTE_ARCH_ARM)
> $(CONFIG_RTE_ARCH_ARM64)),)
> >  SRCS-$(CONFIG_RTE_LIBRTE_VIRTIO_PMD) += virtio_rxtx_simple_neon.c
> >  endif
> >
> > +ifneq ($(FORCE_DISABLE_AVX512), y)
> > +	CC_AVX512_SUPPORT=\
> > +	$(shell $(CC) -march=native -dM -E - </dev/null 2>&1 | \
> > +	sed '/./{H;$$!d} ; x ; /AVX512F/!d; /AVX512BW/!d; /AVX512VL/!d' | \
> > +	grep -q AVX512 && echo 1)
> > +endif
> > +
> > +ifeq ($(CC_AVX512_SUPPORT), 1)
> > +CFLAGS += -DCC_AVX512_SUPPORT
> > +SRCS-$(CONFIG_RTE_LIBRTE_VIRTIO_PMD) += virtio_rxtx_packed_avx.c
> > +
> > +ifeq ($(RTE_TOOLCHAIN), gcc)
> > +ifeq ($(shell test $(GCC_VERSION) -ge 83 && echo 1), 1)
> > +CFLAGS += -DVIRTIO_GCC_UNROLL_PRAGMA
> > +endif
> > +endif
> > +
> > +ifeq ($(RTE_TOOLCHAIN), clang)
> > +ifeq ($(shell test $(CLANG_MAJOR_VERSION)$(CLANG_MINOR_VERSION) -
> ge 37 && echo 1), 1)
> > +CFLAGS += -DVIRTIO_CLANG_UNROLL_PRAGMA
> > +endif
> > +endif
> > +
> > +ifeq ($(RTE_TOOLCHAIN), icc)
> > +ifeq ($(shell test $(ICC_MAJOR_VERSION) -ge 16 && echo 1), 1)
> > +CFLAGS += -DVIRTIO_ICC_UNROLL_PRAGMA
> > +endif
> > +endif
> > +
> > +CFLAGS_virtio_rxtx_packed_avx.o += -mavx512f -mavx512bw -mavx512vl
> > +ifeq ($(shell test $(GCC_VERSION) -ge 100 && echo 1), 1)
> > +CFLAGS_virtio_rxtx_packed_avx.o += -Wno-zero-length-bounds
> > +endif
> > +endif
> > +
> >  ifeq ($(CONFIG_RTE_VIRTIO_USER),y)
> >  SRCS-$(CONFIG_RTE_LIBRTE_VIRTIO_PMD) += virtio_user/vhost_user.c
> >  SRCS-$(CONFIG_RTE_LIBRTE_VIRTIO_PMD) += virtio_user/vhost_kernel.c
> > diff --git a/drivers/net/virtio/meson.build b/drivers/net/virtio/meson.build
> > index 15150eea1..8e68c3039 100644
> > --- a/drivers/net/virtio/meson.build
> > +++ b/drivers/net/virtio/meson.build
> > @@ -9,6 +9,20 @@ sources += files('virtio_ethdev.c',
> >  deps += ['kvargs', 'bus_pci']
> >
> >  if arch_subdir == 'x86'
> > +	if '-mno-avx512f' not in machine_args
> > +		if cc.has_argument('-mavx512f') and cc.has_argument('-
> mavx512vl') and cc.has_argument('-mavx512bw')
> > +			cflags += ['-mavx512f', '-mavx512bw', '-mavx512vl']
> > +			cflags += ['-DCC_AVX512_SUPPORT']
> > +			if (toolchain == 'gcc' and
> cc.version().version_compare('>=8.3.0'))
> > +				cflags += '-DVHOST_GCC_UNROLL_PRAGMA'
> > +			elif (toolchain == 'clang' and
> cc.version().version_compare('>=3.7.0'))
> > +				cflags += '-
> DVHOST_CLANG_UNROLL_PRAGMA'
> > +			elif (toolchain == 'icc' and
> cc.version().version_compare('>=16.0.0'))
> > +				cflags += '-DVHOST_ICC_UNROLL_PRAGMA'
> > +			endif
> > +			sources += files('virtio_rxtx_packed_avx.c')
> > +		endif
> > +	endif
> >  	sources += files('virtio_rxtx_simple_sse.c')
> >  elif arch_subdir == 'ppc'
> >  	sources += files('virtio_rxtx_simple_altivec.c')
> > diff --git a/drivers/net/virtio/virtio_ethdev.h
> b/drivers/net/virtio/virtio_ethdev.h
> > index febaf17a8..5c112cac7 100644
> > --- a/drivers/net/virtio/virtio_ethdev.h
> > +++ b/drivers/net/virtio/virtio_ethdev.h
> > @@ -105,6 +105,9 @@ uint16_t virtio_xmit_pkts_inorder(void *tx_queue,
> struct rte_mbuf **tx_pkts,
> >  uint16_t virtio_recv_pkts_vec(void *rx_queue, struct rte_mbuf **rx_pkts,
> >  		uint16_t nb_pkts);
> >
> > +uint16_t virtio_recv_pkts_packed_vec(void *rx_queue, struct rte_mbuf
> **rx_pkts,
> > +		uint16_t nb_pkts);
> > +
> >  int eth_virtio_dev_init(struct rte_eth_dev *eth_dev);
> >
> >  void virtio_interrupt_handler(void *param);
> > diff --git a/drivers/net/virtio/virtio_rxtx.c b/drivers/net/virtio/virtio_rxtx.c
> > index a549991aa..534562cca 100644
> > --- a/drivers/net/virtio/virtio_rxtx.c
> > +++ b/drivers/net/virtio/virtio_rxtx.c
> > @@ -2030,3 +2030,11 @@ virtio_xmit_pkts_inorder(void *tx_queue,
> >
> >  	return nb_tx;
> >  }
> > +
> > +__rte_weak uint16_t
> > +virtio_recv_pkts_packed_vec(void *rx_queue __rte_unused,
> > +			    struct rte_mbuf **rx_pkts __rte_unused,
> > +			    uint16_t nb_pkts __rte_unused)
> > +{
> > +	return 0;
> > +}
> > diff --git a/drivers/net/virtio/virtio_rxtx_packed_avx.c
> b/drivers/net/virtio/virtio_rxtx_packed_avx.c
> > new file mode 100644
> > index 000000000..8a7b459eb
> > --- /dev/null
> > +++ b/drivers/net/virtio/virtio_rxtx_packed_avx.c
> > @@ -0,0 +1,374 @@
> > +/* SPDX-License-Identifier: BSD-3-Clause
> > + * Copyright(c) 2010-2020 Intel Corporation
> > + */
> > +
> > +#include <stdint.h>
> > +#include <stdio.h>
> > +#include <stdlib.h>
> > +#include <string.h>
> > +#include <errno.h>
> > +
> > +#include <rte_net.h>
> > +
> > +#include "virtio_logs.h"
> > +#include "virtio_ethdev.h"
> > +#include "virtio_pci.h"
> > +#include "virtqueue.h"
> > +
> > +#define BYTE_SIZE 8
> > +/* flag bits offset in packed ring desc higher 64bits */
> > +#define FLAGS_BITS_OFFSET ((offsetof(struct vring_packed_desc, flags) - \
> > +	offsetof(struct vring_packed_desc, len)) * BYTE_SIZE)
> > +
> > +#define PACKED_FLAGS_MASK ((0ULL |
> VRING_PACKED_DESC_F_AVAIL_USED) << \
> > +	FLAGS_BITS_OFFSET)
> > +
> > +#define PACKED_BATCH_SIZE (RTE_CACHE_LINE_SIZE / \
> > +	sizeof(struct vring_packed_desc))
> > +#define PACKED_BATCH_MASK (PACKED_BATCH_SIZE - 1)
> > +
> > +#ifdef VIRTIO_GCC_UNROLL_PRAGMA
> > +#define virtio_for_each_try_unroll(iter, val, size) _Pragma("GCC unroll 4")
> \
> > +	for (iter = val; iter < size; iter++)
> > +#endif
> > +
> > +#ifdef VIRTIO_CLANG_UNROLL_PRAGMA
> > +#define virtio_for_each_try_unroll(iter, val, size) _Pragma("unroll 4") \
> > +	for (iter = val; iter < size; iter++)
> > +#endif
> > +
> > +#ifdef VIRTIO_ICC_UNROLL_PRAGMA
> > +#define virtio_for_each_try_unroll(iter, val, size) _Pragma("unroll (4)") \
> > +	for (iter = val; iter < size; iter++)
> > +#endif
> > +
> > +#ifndef virtio_for_each_try_unroll
> > +#define virtio_for_each_try_unroll(iter, val, num) \
> > +	for (iter = val; iter < num; iter++)
> > +#endif
> > +
> > +static inline void
> > +virtio_update_batch_stats(struct virtnet_stats *stats,
> > +			  uint16_t pkt_len1,
> > +			  uint16_t pkt_len2,
> > +			  uint16_t pkt_len3,
> > +			  uint16_t pkt_len4)
> > +{
> > +	stats->bytes += pkt_len1;
> > +	stats->bytes += pkt_len2;
> > +	stats->bytes += pkt_len3;
> > +	stats->bytes += pkt_len4;
> > +}
> > +
> > +/* Optionally fill offload information in structure */
> > +static inline int
> > +virtio_vec_rx_offload(struct rte_mbuf *m, struct virtio_net_hdr *hdr)
> > +{
> > +	struct rte_net_hdr_lens hdr_lens;
> > +	uint32_t hdrlen, ptype;
> > +	int l4_supported = 0;
> > +
> > +	/* nothing to do */
> > +	if (hdr->flags == 0)
> > +		return 0;
> > +
> > +	/* GSO not support in vec path, skip check */
> > +	m->ol_flags |= PKT_RX_IP_CKSUM_UNKNOWN;
> > +
> > +	ptype = rte_net_get_ptype(m, &hdr_lens, RTE_PTYPE_ALL_MASK);
> > +	m->packet_type = ptype;
> > +	if ((ptype & RTE_PTYPE_L4_MASK) == RTE_PTYPE_L4_TCP ||
> > +	    (ptype & RTE_PTYPE_L4_MASK) == RTE_PTYPE_L4_UDP ||
> > +	    (ptype & RTE_PTYPE_L4_MASK) == RTE_PTYPE_L4_SCTP)
> > +		l4_supported = 1;
> > +
> > +	if (hdr->flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) {
> > +		hdrlen = hdr_lens.l2_len + hdr_lens.l3_len + hdr_lens.l4_len;
> > +		if (hdr->csum_start <= hdrlen && l4_supported) {
> > +			m->ol_flags |= PKT_RX_L4_CKSUM_NONE;
> > +		} else {
> > +			/* Unknown proto or tunnel, do sw cksum. We can
> assume
> > +			 * the cksum field is in the first segment since the
> > +			 * buffers we provided to the host are large enough.
> > +			 * In case of SCTP, this will be wrong since it's a CRC
> > +			 * but there's nothing we can do.
> > +			 */
> > +			uint16_t csum = 0, off;
> > +
> > +			rte_raw_cksum_mbuf(m, hdr->csum_start,
> > +				rte_pktmbuf_pkt_len(m) - hdr->csum_start,
> > +				&csum);
> > +			if (likely(csum != 0xffff))
> > +				csum = ~csum;
> > +			off = hdr->csum_offset + hdr->csum_start;
> > +			if (rte_pktmbuf_data_len(m) >= off + 1)
> > +				*rte_pktmbuf_mtod_offset(m, uint16_t *,
> > +					off) = csum;
> > +		}
> > +	} else if (hdr->flags & VIRTIO_NET_HDR_F_DATA_VALID &&
> l4_supported) {
> > +		m->ol_flags |= PKT_RX_L4_CKSUM_GOOD;
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> > +static inline uint16_t
> > +virtqueue_dequeue_batch_packed_vec(struct virtnet_rx *rxvq,
> > +				   struct rte_mbuf **rx_pkts)
> > +{
> > +	struct virtqueue *vq = rxvq->vq;
> > +	struct virtio_hw *hw = vq->hw;
> > +	uint16_t hdr_size = hw->vtnet_hdr_size;
> > +	uint64_t addrs[PACKED_BATCH_SIZE];
> > +	uint16_t id = vq->vq_used_cons_idx;
> > +	uint8_t desc_stats;
> > +	uint16_t i;
> > +	void *desc_addr;
> > +
> > +	if (id & PACKED_BATCH_MASK)
> > +		return -1;
> > +
> > +	if (unlikely((id + PACKED_BATCH_SIZE) > vq->vq_nentries))
> > +		return -1;
> > +
> > +	/* only care avail/used bits */
> > +	__m512i v_mask = _mm512_maskz_set1_epi64(0xaa,
> PACKED_FLAGS_MASK);
> > +	desc_addr = &vq->vq_packed.ring.desc[id];
> > +
> > +	__m512i v_desc = _mm512_loadu_si512(desc_addr);
> > +	__m512i v_flag = _mm512_and_epi64(v_desc, v_mask);
> > +
> > +	__m512i v_used_flag = _mm512_setzero_si512();
> > +	if (vq->vq_packed.used_wrap_counter)
> > +		v_used_flag = _mm512_maskz_set1_epi64(0xaa,
> PACKED_FLAGS_MASK);
> > +
> > +	/* Check all descs are used */
> > +	desc_stats = _mm512_cmpneq_epu64_mask(v_flag, v_used_flag);
> > +	if (desc_stats)
> > +		return -1;
> > +
> > +	virtio_for_each_try_unroll(i, 0, PACKED_BATCH_SIZE) {
> > +		rx_pkts[i] = (struct rte_mbuf *)vq->vq_descx[id + i].cookie;
> > +		rte_packet_prefetch(rte_pktmbuf_mtod(rx_pkts[i], void *));
> > +
> > +		addrs[i] = (uint64_t)rx_pkts[i]->rx_descriptor_fields1;
> > +	}
> > +
> > +	/*
> > +	 * load len from desc, store into mbuf pkt_len and data_len
> > +	 * len limiated by l6bit buf_len, pkt_len[16:31] can be ignored
> > +	 */
> > +	const __mmask16 mask = 0x6 | 0x6 << 4 | 0x6 << 8 | 0x6 << 12;
> > +	__m512i values = _mm512_maskz_shuffle_epi32(mask, v_desc,
> 0xAA);
> > +
> > +	/* reduce hdr_len from pkt_len and data_len */
> > +	__m512i mbuf_len_offset = _mm512_maskz_set1_epi32(mask,
> > +			(uint32_t)-hdr_size);
> > +
> > +	__m512i v_value = _mm512_add_epi32(values, mbuf_len_offset);
> > +
> > +	/* assert offset of data_len */
> > +	RTE_BUILD_BUG_ON(offsetof(struct rte_mbuf, data_len) !=
> > +		offsetof(struct rte_mbuf, rx_descriptor_fields1) + 8);
> > +
> > +	__m512i v_index = _mm512_set_epi64(addrs[3] + 8, addrs[3],
> > +					   addrs[2] + 8, addrs[2],
> > +					   addrs[1] + 8, addrs[1],
> > +					   addrs[0] + 8, addrs[0]);
> > +	/* batch store into mbufs */
> > +	_mm512_i64scatter_epi64(0, v_index, v_value, 1);
> > +
> > +	if (hw->has_rx_offload) {
> > +		virtio_for_each_try_unroll(i, 0, PACKED_BATCH_SIZE) {
> > +			char *addr = (char *)rx_pkts[i]->buf_addr +
> > +				RTE_PKTMBUF_HEADROOM - hdr_size;
> > +			virtio_vec_rx_offload(rx_pkts[i],
> > +					(struct virtio_net_hdr *)addr);
> > +		}
> > +	}
> > +
> > +	virtio_update_batch_stats(&rxvq->stats, rx_pkts[0]->pkt_len,
> > +			rx_pkts[1]->pkt_len, rx_pkts[2]->pkt_len,
> > +			rx_pkts[3]->pkt_len);
> > +
> > +	vq->vq_free_cnt += PACKED_BATCH_SIZE;
> > +
> > +	vq->vq_used_cons_idx += PACKED_BATCH_SIZE;
> > +	if (vq->vq_used_cons_idx >= vq->vq_nentries) {
> > +		vq->vq_used_cons_idx -= vq->vq_nentries;
> > +		vq->vq_packed.used_wrap_counter ^= 1;
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> > +static uint16_t
> > +virtqueue_dequeue_single_packed_vec(struct virtnet_rx *rxvq,
> > +				    struct rte_mbuf **rx_pkts)
> > +{
> > +	uint16_t used_idx, id;
> > +	uint32_t len;
> > +	struct virtqueue *vq = rxvq->vq;
> > +	struct virtio_hw *hw = vq->hw;
> > +	uint32_t hdr_size = hw->vtnet_hdr_size;
> > +	struct virtio_net_hdr *hdr;
> > +	struct vring_packed_desc *desc;
> > +	struct rte_mbuf *cookie;
> > +
> > +	desc = vq->vq_packed.ring.desc;
> > +	used_idx = vq->vq_used_cons_idx;
> > +	if (!desc_is_used(&desc[used_idx], vq))
> > +		return -1;
> > +
> > +	len = desc[used_idx].len;
> > +	id = desc[used_idx].id;
> > +	cookie = (struct rte_mbuf *)vq->vq_descx[id].cookie;
> > +	if (unlikely(cookie == NULL)) {
> > +		PMD_DRV_LOG(ERR, "vring descriptor with no mbuf cookie
> at %u",
> > +				vq->vq_used_cons_idx);
> > +		return -1;
> > +	}
> > +	rte_prefetch0(cookie);
> > +	rte_packet_prefetch(rte_pktmbuf_mtod(cookie, void *));
> > +
> > +	cookie->data_off = RTE_PKTMBUF_HEADROOM;
> > +	cookie->ol_flags = 0;
> > +	cookie->pkt_len = (uint32_t)(len - hdr_size);
> > +	cookie->data_len = (uint32_t)(len - hdr_size);
> > +
> > +	hdr = (struct virtio_net_hdr *)((char *)cookie->buf_addr +
> > +					RTE_PKTMBUF_HEADROOM -
> hdr_size);
> > +	if (hw->has_rx_offload)
> > +		virtio_vec_rx_offload(cookie, hdr);
> > +
> > +	*rx_pkts = cookie;
> > +
> > +	rxvq->stats.bytes += cookie->pkt_len;
> > +
> > +	vq->vq_free_cnt++;
> > +	vq->vq_used_cons_idx++;
> > +	if (vq->vq_used_cons_idx >= vq->vq_nentries) {
> > +		vq->vq_used_cons_idx -= vq->vq_nentries;
> > +		vq->vq_packed.used_wrap_counter ^= 1;
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> > +static inline void
> > +virtio_recv_refill_packed_vec(struct virtnet_rx *rxvq,
> > +			      struct rte_mbuf **cookie,
> > +			      uint16_t num)
> > +{
> > +	struct virtqueue *vq = rxvq->vq;
> > +	struct vring_packed_desc *start_dp = vq->vq_packed.ring.desc;
> > +	uint16_t flags = vq->vq_packed.cached_flags;
> > +	struct virtio_hw *hw = vq->hw;
> > +	struct vq_desc_extra *dxp;
> > +	uint16_t idx, i;
> > +	uint16_t batch_num, total_num = 0;
> > +	uint16_t head_idx = vq->vq_avail_idx;
> > +	uint16_t head_flag = vq->vq_packed.cached_flags;
> > +	uint64_t addr;
> > +
> > +	do {
> > +		idx = vq->vq_avail_idx;
> > +
> > +		batch_num = PACKED_BATCH_SIZE;
> > +		if (unlikely((idx + PACKED_BATCH_SIZE) > vq->vq_nentries))
> > +			batch_num = vq->vq_nentries - idx;
> > +		if (unlikely((total_num + batch_num) > num))
> > +			batch_num = num - total_num;
> > +
> > +		virtio_for_each_try_unroll(i, 0, batch_num) {
> > +			dxp = &vq->vq_descx[idx + i];
> > +			dxp->cookie = (void *)cookie[total_num + i];
> > +
> > +			addr = VIRTIO_MBUF_ADDR(cookie[total_num + i],
> vq) +
> > +				RTE_PKTMBUF_HEADROOM - hw-
> >vtnet_hdr_size;
> > +			start_dp[idx + i].addr = addr;
> > +			start_dp[idx + i].len = cookie[total_num + i]->buf_len
> > +				- RTE_PKTMBUF_HEADROOM + hw-
> >vtnet_hdr_size;
> > +			if (total_num || i) {
> > +				virtqueue_store_flags_packed(&start_dp[idx
> + i],
> > +						flags, hw->weak_barriers);
> > +			}
> > +		}
> > +
> > +		vq->vq_avail_idx += batch_num;
> > +		if (vq->vq_avail_idx >= vq->vq_nentries) {
> > +			vq->vq_avail_idx -= vq->vq_nentries;
> > +			vq->vq_packed.cached_flags ^=
> > +				VRING_PACKED_DESC_F_AVAIL_USED;
> > +			flags = vq->vq_packed.cached_flags;
> > +		}
> > +		total_num += batch_num;
> > +	} while (total_num < num);
> > +
> > +	virtqueue_store_flags_packed(&start_dp[head_idx], head_flag,
> > +				hw->weak_barriers);
> > +	vq->vq_free_cnt = (uint16_t)(vq->vq_free_cnt - num);
> > +}
> > +
> > +uint16_t
> > +virtio_recv_pkts_packed_vec(void *rx_queue,
> > +			    struct rte_mbuf **rx_pkts,
> > +			    uint16_t nb_pkts)
> > +{
> > +	struct virtnet_rx *rxvq = rx_queue;
> > +	struct virtqueue *vq = rxvq->vq;
> > +	struct virtio_hw *hw = vq->hw;
> > +	uint16_t num, nb_rx = 0;
> > +	uint32_t nb_enqueued = 0;
> > +	uint16_t free_cnt = vq->vq_free_thresh;
> > +
> > +	if (unlikely(hw->started == 0))
> > +		return nb_rx;
> > +
> > +	num = RTE_MIN(VIRTIO_MBUF_BURST_SZ, nb_pkts);
> > +	if (likely(num > PACKED_BATCH_SIZE))
> > +		num = num - ((vq->vq_used_cons_idx + num) %
> PACKED_BATCH_SIZE);
> > +
> > +	while (num) {
> > +		if (!virtqueue_dequeue_batch_packed_vec(rxvq,
> > +					&rx_pkts[nb_rx])) {
> > +			nb_rx += PACKED_BATCH_SIZE;
> > +			num -= PACKED_BATCH_SIZE;
> > +			continue;
> > +		}
> > +		if (!virtqueue_dequeue_single_packed_vec(rxvq,
> > +					&rx_pkts[nb_rx])) {
> > +			nb_rx++;
> > +			num--;
> > +			continue;
> > +		}
> > +		break;
> > +	};
> > +
> > +	PMD_RX_LOG(DEBUG, "dequeue:%d", num);
> > +
> > +	rxvq->stats.packets += nb_rx;
> > +
> > +	if (likely(vq->vq_free_cnt >= free_cnt)) {
> > +		struct rte_mbuf *new_pkts[free_cnt];
> > +		if (likely(rte_pktmbuf_alloc_bulk(rxvq->mpool, new_pkts,
> > +						free_cnt) == 0)) {
> > +			virtio_recv_refill_packed_vec(rxvq, new_pkts,
> > +					free_cnt);
> > +			nb_enqueued += free_cnt;
> > +		} else {
> > +			struct rte_eth_dev *dev =
> > +				&rte_eth_devices[rxvq->port_id];
> > +			dev->data->rx_mbuf_alloc_failed += free_cnt;
> > +		}
> > +	}
> > +
> > +	if (likely(nb_enqueued)) {
> > +		if (unlikely(virtqueue_kick_prepare_packed(vq))) {
> > +			virtqueue_notify(vq);
> > +			PMD_RX_LOG(DEBUG, "Notified");
> > +		}
> > +	}
> > +
> > +	return nb_rx;
> > +}
> > diff --git a/drivers/net/virtio/virtio_user_ethdev.c
> b/drivers/net/virtio/virtio_user_ethdev.c
> > index 40ad786cc..c54698ad1 100644
> > --- a/drivers/net/virtio/virtio_user_ethdev.c
> > +++ b/drivers/net/virtio/virtio_user_ethdev.c
> > @@ -528,6 +528,7 @@ virtio_user_eth_dev_alloc(struct rte_vdev_device
> *vdev)
> >  	hw->use_msix = 1;
> >  	hw->modern   = 0;
> >  	hw->use_vec_rx = 0;
> > +	hw->use_vec_tx = 0;
> >  	hw->use_inorder_rx = 0;
> >  	hw->use_inorder_tx = 0;
> >  	hw->virtio_user_dev = dev;
> > @@ -739,8 +740,19 @@ virtio_user_pmd_probe(struct rte_vdev_device
> *dev)
> >  		goto end;
> >  	}
> >
> > -	if (vectorized)
> > -		hw->use_vec_rx = 1;
> > +	if (vectorized) {
> > +		if (packed_vq) {
> > +#if defined(CC_AVX512_SUPPORT)
> > +			hw->use_vec_rx = 1;
> > +			hw->use_vec_tx = 1;
> > +#else
> > +			PMD_INIT_LOG(INFO,
> > +				"building environment do not support packed
> ring vectorized");
> > +#endif
> > +		} else {
> > +			hw->use_vec_rx = 1;
> > +		}
> > +	}
> >
> >  	rte_eth_dev_probing_finish(eth_dev);
> >  	ret = 0;
> > diff --git a/drivers/net/virtio/virtqueue.h b/drivers/net/virtio/virtqueue.h
> > index ca1c10499..ce0340743 100644
> > --- a/drivers/net/virtio/virtqueue.h
> > +++ b/drivers/net/virtio/virtqueue.h
> > @@ -239,7 +239,8 @@ struct vq_desc_extra {
> >  	void *cookie;
> >  	uint16_t ndescs;
> >  	uint16_t next;
> > -};
> > +	uint8_t padding[4];
> > +} __rte_packed __rte_aligned(16);
> 
> Can't this introduce a performance impact for the non-vectorized
> case? I think of worse cache liens utilization.
> 
> For example with a burst of 32 descriptors with 32B cachelines, before
> it would take 14 cachelines, after 16. So for each burst, one could face
> 2 extra cache misses.
> 
> If you could run non-vectorized benchamrks with and without that patch,
> I would be grateful.
> 

Maxime,
Thanks for point it out, it will add extra cache miss in datapath. 
And its impact on performance is around 1% in loopback case. 
While benefit of vectorized path will be more than that number.

Thanks,
Marvin

> Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> 
> Thanks,
> Maxime