[dpdk-dev] [PATCH v2 5/5] vhost: add packed ring vectorized enqueue

[Maxime Coquelin]

On 9/21/20 8:48 AM, Marvin Liu wrote:
> Optimize vhost packed ring enqueue path with SIMD instructions. Four
> descriptors status and length are batched handled with AVX512
> instructions. Address translation operations are also accelerated
> by AVX512 instructions.
> 
> Signed-off-by: Marvin Liu <yong.liu at intel.com>
> 
> diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
> index fc7daf2145..b78b2c5c1b 100644
> --- a/lib/librte_vhost/vhost.h
> +++ b/lib/librte_vhost/vhost.h
> @@ -1132,4 +1132,10 @@ vhost_reserve_avail_batch_packed_avx(struct virtio_net *dev,
>  				 uint16_t avail_idx,
>  				 uintptr_t *desc_addrs,
>  				 uint16_t *ids);
> +
> +int
> +virtio_dev_rx_batch_packed_avx(struct virtio_net *dev,
> +			       struct vhost_virtqueue *vq,
> +			       struct rte_mbuf **pkts);
> +
>  #endif /* _VHOST_NET_CDEV_H_ */
> diff --git a/lib/librte_vhost/vhost_vec_avx.c b/lib/librte_vhost/vhost_vec_avx.c
> index dc5322d002..7d2250ed86 100644
> --- a/lib/librte_vhost/vhost_vec_avx.c
> +++ b/lib/librte_vhost/vhost_vec_avx.c
> @@ -35,9 +35,15 @@
>  #define PACKED_AVAIL_FLAG ((0ULL | VRING_DESC_F_AVAIL) << FLAGS_BITS_OFFSET)
>  #define PACKED_AVAIL_FLAG_WRAP ((0ULL | VRING_DESC_F_USED) << \
>  	FLAGS_BITS_OFFSET)
> +#define PACKED_WRITE_AVAIL_FLAG (PACKED_AVAIL_FLAG | \
> +	((0ULL | VRING_DESC_F_WRITE) << FLAGS_BITS_OFFSET))
> +#define PACKED_WRITE_AVAIL_FLAG_WRAP (PACKED_AVAIL_FLAG_WRAP | \
> +	((0ULL | VRING_DESC_F_WRITE) << FLAGS_BITS_OFFSET))
>  
>  #define DESC_FLAGS_POS 0xaa
>  #define MBUF_LENS_POS 0x6666
> +#define DESC_LENS_POS 0x4444
> +#define DESC_LENS_FLAGS_POS 0xB0B0B0B0
>  
>  int
>  vhost_reserve_avail_batch_packed_avx(struct virtio_net *dev,
> @@ -179,3 +185,154 @@ vhost_reserve_avail_batch_packed_avx(struct virtio_net *dev,
>  
>  	return -1;
>  }
> +
> +int
> +virtio_dev_rx_batch_packed_avx(struct virtio_net *dev,
> +			       struct vhost_virtqueue *vq,
> +			       struct rte_mbuf **pkts)
> +{
> +	struct vring_packed_desc *descs = vq->desc_packed;
> +	uint16_t avail_idx = vq->last_avail_idx;
> +	uint64_t desc_addrs[PACKED_BATCH_SIZE];
> +	uint32_t buf_offset = dev->vhost_hlen;
> +	uint32_t desc_status;
> +	uint64_t lens[PACKED_BATCH_SIZE];
> +	uint16_t i;
> +	void *desc_addr;
> +	uint8_t cmp_low, cmp_high, cmp_result;
> +
> +	if (unlikely(avail_idx & PACKED_BATCH_MASK))
> +		return -1;

Same comment as for patch 4. Packed ring size may not be a pow2.

> +	/* check refcnt and nb_segs */
> +	__m256i mbuf_ref = _mm256_set1_epi64x(DEFAULT_REARM_DATA);
> +
> +	/* load four mbufs rearm data */
> +	__m256i mbufs = _mm256_set_epi64x(
> +				*pkts[3]->rearm_data,
> +				*pkts[2]->rearm_data,
> +				*pkts[1]->rearm_data,
> +				*pkts[0]->rearm_data);
> +
> +	uint16_t cmp = _mm256_cmpneq_epu16_mask(mbufs, mbuf_ref);
> +	if (cmp & MBUF_LENS_POS)
> +		return -1;
> +
> +	/* check desc status */
> +	desc_addr = &vq->desc_packed[avail_idx];
> +	__m512i desc_vec = _mm512_loadu_si512(desc_addr);
> +
> +	__m512i avail_flag_vec;
> +	__m512i used_flag_vec;
> +	if (vq->avail_wrap_counter) {
> +#if defined(RTE_ARCH_I686)

Is supporting AVX512 on i686 really useful/necessary?

> +		avail_flag_vec = _mm512_set4_epi64(PACKED_WRITE_AVAIL_FLAG,
> +					0x0, PACKED_WRITE_AVAIL_FLAG, 0x0);
> +		used_flag_vec = _mm512_set4_epi64(PACKED_FLAGS_MASK, 0x0,
> +					PACKED_FLAGS_MASK, 0x0);
> +#else
> +		avail_flag_vec = _mm512_maskz_set1_epi64(DESC_FLAGS_POS,
> +					PACKED_WRITE_AVAIL_FLAG);
> +		used_flag_vec = _mm512_maskz_set1_epi64(DESC_FLAGS_POS,
> +					PACKED_FLAGS_MASK);
> +#endif
> +	} else {
> +#if defined(RTE_ARCH_I686)
> +		avail_flag_vec = _mm512_set4_epi64(
> +					PACKED_WRITE_AVAIL_FLAG_WRAP, 0x0,
> +					PACKED_WRITE_AVAIL_FLAG, 0x0);
> +		used_flag_vec = _mm512_set4_epi64(0x0, 0x0, 0x0, 0x0);
> +#else
> +		avail_flag_vec = _mm512_maskz_set1_epi64(DESC_FLAGS_POS,
> +					PACKED_WRITE_AVAIL_FLAG_WRAP);
> +		used_flag_vec = _mm512_setzero_epi32();
> +#endif
> +	}
> +
> +	desc_status = _mm512_mask_cmp_epu16_mask(BATCH_FLAGS_MASK, desc_vec,
> +				avail_flag_vec, _MM_CMPINT_NE);
> +	if (desc_status)
> +		return -1;
> +
> +	if (dev->features & (1ULL << VIRTIO_F_IOMMU_PLATFORM)) {
> +		vhost_for_each_try_unroll(i, 0, PACKED_BATCH_SIZE) {
> +			uint64_t size = (uint64_t)descs[avail_idx + i].len;
> +			desc_addrs[i] = __vhost_iova_to_vva(dev, vq,
> +				descs[avail_idx + i].addr, &size,
> +				VHOST_ACCESS_RW);
> +
> +			if (!desc_addrs[i])
> +				return -1;
> +
> +			rte_prefetch0(rte_pktmbuf_mtod_offset(pkts[i], void *,
> +					0));
> +		}
> +	} else {
> +		/* check buffer fit into one region & translate address */
> +		__m512i regions_low_addrs =
> +			_mm512_loadu_si512((void *)&dev->regions_low_addrs);
> +		__m512i regions_high_addrs =
> +			_mm512_loadu_si512((void *)&dev->regions_high_addrs);
> +		vhost_for_each_try_unroll(i, 0, PACKED_BATCH_SIZE) {
> +			uint64_t addr_low = descs[avail_idx + i].addr;
> +			uint64_t addr_high = addr_low +
> +						descs[avail_idx + i].len;
> +			__m512i low_addr_vec = _mm512_set1_epi64(addr_low);
> +			__m512i high_addr_vec = _mm512_set1_epi64(addr_high);
> +
> +			cmp_low = _mm512_cmp_epi64_mask(low_addr_vec,
> +					regions_low_addrs, _MM_CMPINT_NLT);
> +			cmp_high = _mm512_cmp_epi64_mask(high_addr_vec,
> +					regions_high_addrs, _MM_CMPINT_LT);
> +			cmp_result = cmp_low & cmp_high;
> +			int index = __builtin_ctz(cmp_result);
> +			if (unlikely((uint32_t)index >= dev->mem->nregions))
> +				return -1;
> +
> +			desc_addrs[i] = addr_low +
> +				dev->mem->regions[index].host_user_addr -
> +				dev->mem->regions[index].guest_phys_addr;
> +			rte_prefetch0(rte_pktmbuf_mtod_offset(pkts[i], void *,
> +					0));
> +		}
> +	}
> +
> +	/* check length is enough */
> +	__m512i pkt_lens = _mm512_set_epi32(
> +			0, pkts[3]->pkt_len, 0, 0,
> +			0, pkts[2]->pkt_len, 0, 0,
> +			0, pkts[1]->pkt_len, 0, 0,
> +			0, pkts[0]->pkt_len, 0, 0);
> +
> +	__m512i mbuf_len_offset = _mm512_maskz_set1_epi32(DESC_LENS_POS,
> +					dev->vhost_hlen);
> +	__m512i buf_len_vec = _mm512_add_epi32(pkt_lens, mbuf_len_offset);
> +	uint16_t lens_cmp = _mm512_mask_cmp_epu32_mask(DESC_LENS_POS,
> +				desc_vec, buf_len_vec, _MM_CMPINT_LT);
> +	if (lens_cmp)
> +		return -1;
> +
> +	vhost_for_each_try_unroll(i, 0, PACKED_BATCH_SIZE) {
> +		rte_memcpy((void *)(uintptr_t)(desc_addrs[i] + buf_offset),
> +			   rte_pktmbuf_mtod_offset(pkts[i], void *, 0),
> +			   pkts[i]->pkt_len);
> +	}
> +
> +	if (unlikely((dev->features & (1ULL << VHOST_F_LOG_ALL)))) {
> +		vhost_for_each_try_unroll(i, 0, PACKED_BATCH_SIZE) {
> +			lens[i] = descs[avail_idx + i].len;
> +			vhost_log_cache_write_iova(dev, vq,
> +				descs[avail_idx + i].addr, lens[i]);
> +		}
> +	}
> +
> +	vq_inc_last_avail_packed(vq, PACKED_BATCH_SIZE);
> +	vq_inc_last_used_packed(vq, PACKED_BATCH_SIZE);
> +	/* save len and flags, skip addr and id */
> +	__m512i desc_updated = _mm512_mask_add_epi16(desc_vec,
> +					DESC_LENS_FLAGS_POS, buf_len_vec,
> +					used_flag_vec);
> +	_mm512_storeu_si512(desc_addr, desc_updated);
> +
> +	return 0;
> +}
> diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c
> index e4d2e2e7d6..5c56a8d6ff 100644
> --- a/lib/librte_vhost/virtio_net.c
> +++ b/lib/librte_vhost/virtio_net.c
> @@ -1354,6 +1354,21 @@ virtio_dev_rx_single_packed(struct virtio_net *dev,
>  	return 0;
>  }
>  
> +static __rte_always_inline int
> +virtio_dev_rx_handle_batch_packed(struct virtio_net *dev,
> +			   struct vhost_virtqueue *vq,
> +			   struct rte_mbuf **pkts)
> +
> +{
> +	if (unlikely(dev->vectorized))
> +#ifdef CC_AVX512_SUPPORT
> +		return virtio_dev_rx_batch_packed_avx(dev, vq, pkts);
> +#else
> +		return virtio_dev_rx_batch_packed(dev, vq, pkts);
> +#endif
> +	return virtio_dev_rx_batch_packed(dev, vq, pkts);

It should be as below to not have any performance impact when
CC_AVX512_SUPPORT is not set:

#ifdef CC_AVX512_SUPPORT
	if (unlikely(dev->vectorized))
		return virtio_dev_rx_batch_packed_avx(dev, vq, pkts);
#else
	return virtio_dev_rx_batch_packed(dev, vq, pkts);
#endif

> +}
> +
>  static __rte_noinline uint32_t
>  virtio_dev_rx_packed(struct virtio_net *dev,
>  		     struct vhost_virtqueue *__rte_restrict vq,
> @@ -1367,8 +1382,8 @@ virtio_dev_rx_packed(struct virtio_net *dev,
>  		rte_prefetch0(&vq->desc_packed[vq->last_avail_idx]);
>  
>  		if (remained >= PACKED_BATCH_SIZE) {
> -			if (!virtio_dev_rx_batch_packed(dev, vq,
> -							&pkts[pkt_idx])) {
> +			if (!virtio_dev_rx_handle_batch_packed(dev, vq,
> +				&pkts[pkt_idx])) {
>  				pkt_idx += PACKED_BATCH_SIZE;
>  				remained -= PACKED_BATCH_SIZE;
>  				continue;
>