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

[Maxime Coquelin <maxime.coquelin@redhat.com>]

On 4/28/20 3:14 AM, Liu, Yong wrote:
> 
> 
>> -----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. 

Ok, thanks for doing the test. I'll try to run some PVP benchmarks
on my side because when doing IO loopback, the cache pressure is
much less important.

> While benefit of vectorized path will be more than that number.

Ok, but I disagree for two reasons:
 1. You have to keep in mind than non-vectorized is the default and
encouraged mode to use. Indeed, it takes a lot of shortcuts like not
checking header length (so no error stats), etc...

 2. It's like saying it's OK it degrades by 5% on $CPU_VENDOR_A because
the gain is 20% on $CPU_VENDOR_B.

In the case we see more degradation in real-world scenario, you might
want to consider using ifdefs to avoid adding padding in the non-
vectorized case, like you did to differentiate Virtio PMD to Virtio-user
PMD in patch 7.

Thanks,
Maxime

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