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

[Liu, Yong]

> -----Original Message-----
> From: Maxime Coquelin <maxime.coquelin at redhat.com>
> Sent: Tuesday, October 6, 2020 11:00 PM
> To: Liu, Yong <yong.liu at intel.com>; Xia, Chenbo <chenbo.xia at intel.com>;
> Wang, Zhihong <zhihong.wang at intel.com>
> Cc: dev at dpdk.org
> Subject: Re: [PATCH v2 5/5] vhost: add packed ring vectorized enqueue
> 
> 
> 
> 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.
> 
Thanks, will fix in next version.

> > +	/* 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?
> 
It is useless for function point of view.  Here is for successful compilation if enabled i686 build. 

> > +		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
> 
Got, will fix in next version.

> > +}
> > +
> >  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;
> >