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To: Marvin Liu <yong.liu@intel.com>, chenbo.xia@intel.com,
zhihong.wang@intel.com
Cc: dev@dpdk.org
References: <20200819032414.51430-1-yong.liu@intel.com>
<20200819032414.51430-5-yong.liu@intel.com>
From: Maxime Coquelin <maxime.coquelin@redhat.com>
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Date: Fri, 18 Sep 2020 15:44:50 +0200
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Subject: Re: [dpdk-dev] [PATCH v1 4/5] vhost: add packed ring vectorized
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On 8/19/20 5:24 AM, Marvin Liu wrote:
> Optimize vhost packed ring dequeue path with SIMD instructions. Four
> descriptors status check and writeback are batched handled with AVX512
> instructions. Address translation operations are also accelerated by
> AVX512 instructions.
>
> If platform or compiler not support vectorization, will fallback to
> default path.
>
> Signed-off-by: Marvin Liu <yong.liu@intel.com>
>
> diff --git a/lib/librte_vhost/Makefile b/lib/librte_vhost/Makefile
> index 4f2f3e47da..c0cd7d498f 100644
> --- a/lib/librte_vhost/Makefile
> +++ b/lib/librte_vhost/Makefile
> @@ -31,6 +31,13 @@ CFLAGS += -DVHOST_ICC_UNROLL_PRAGMA
> endif
> 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 ($(CONFIG_RTE_LIBRTE_VHOST_NUMA),y)
> LDLIBS += -lnuma
> endif
> @@ -40,6 +47,12 @@ LDLIBS += -lrte_eal -lrte_mempool -lrte_mbuf -lrte_ethdev -lrte_net
> SRCS-$(CONFIG_RTE_LIBRTE_VHOST) := fd_man.c iotlb.c socket.c vhost.c \
> vhost_user.c virtio_net.c vdpa.c
>
> +ifeq ($(CC_AVX512_SUPPORT), 1)
> +CFLAGS += -DCC_AVX512_SUPPORT
> +SRCS-$(CONFIG_RTE_LIBRTE_VHOST) += vhost_vec_avx.c
> +CFLAGS_vhost_vec_avx.o += -mavx512f -mavx512bw -mavx512vl
> +endif
> +
> # install includes
> SYMLINK-$(CONFIG_RTE_LIBRTE_VHOST)-include += rte_vhost.h rte_vdpa.h \
> rte_vdpa_dev.h rte_vhost_async.h
> diff --git a/lib/librte_vhost/meson.build b/lib/librte_vhost/meson.build
> index cc9aa65c67..c1481802d7 100644
> --- a/lib/librte_vhost/meson.build
> +++ b/lib/librte_vhost/meson.build
> @@ -8,6 +8,22 @@ endif
> if has_libnuma == 1
> dpdk_conf.set10('RTE_LIBRTE_VHOST_NUMA', true)
> endif
> +
> +if arch_subdir == 'x86'
> + if not machine_args.contains('-mno-avx512f')
> + if cc.has_argument('-mavx512f') and cc.has_argument('-mavx512vl') and cc.has_argument('-mavx512bw')
> + cflags += ['-DCC_AVX512_SUPPORT']
> + vhost_avx512_lib = static_library('vhost_avx512_lib',
> + 'vhost_vec_avx.c',
> + dependencies: [static_rte_eal, static_rte_mempool,
> + static_rte_mbuf, static_rte_ethdev, static_rte_net],
> + include_directories: includes,
> + c_args: [cflags, '-mavx512f', '-mavx512bw', '-mavx512vl'])
> + objs += vhost_avx512_lib.extract_objects('vhost_vec_avx.c')
> + endif
> + endif
> +endif
> +
> 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'))
> diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
> index 4a81f18f01..fc7daf2145 100644
> --- a/lib/librte_vhost/vhost.h
> +++ b/lib/librte_vhost/vhost.h
> @@ -1124,4 +1124,12 @@ virtio_dev_pktmbuf_alloc(struct virtio_net *dev, struct rte_mempool *mp,
> return NULL;
> }
>
> +int
> +vhost_reserve_avail_batch_packed_avx(struct virtio_net *dev,
> + struct vhost_virtqueue *vq,
> + struct rte_mempool *mbuf_pool,
> + struct rte_mbuf **pkts,
> + uint16_t avail_idx,
> + uintptr_t *desc_addrs,
> + uint16_t *ids);
> #endif /* _VHOST_NET_CDEV_H_ */
> diff --git a/lib/librte_vhost/vhost_vec_avx.c b/lib/librte_vhost/vhost_vec_avx.c
> new file mode 100644
> index 0000000000..e8361d18fa
> --- /dev/null
> +++ b/lib/librte_vhost/vhost_vec_avx.c
> @@ -0,0 +1,152 @@
> +/* SPDX-License-Identifier: BSD-3-Clause
> + * Copyright(c) 2010-2016 Intel Corporation
> + */
> +#include <stdint.h>
> +
> +#include "vhost.h"
> +
> +#define BYTE_SIZE 8
> +/* reference count offset in mbuf rearm data */
> +#define REFCNT_BITS_OFFSET ((offsetof(struct rte_mbuf, refcnt) - \
> + offsetof(struct rte_mbuf, rearm_data)) * BYTE_SIZE)
> +/* segment number offset in mbuf rearm data */
> +#define SEG_NUM_BITS_OFFSET ((offsetof(struct rte_mbuf, nb_segs) - \
> + offsetof(struct rte_mbuf, rearm_data)) * BYTE_SIZE)
> +
> +/* default rearm data */
> +#define DEFAULT_REARM_DATA (1ULL << SEG_NUM_BITS_OFFSET | \
> + 1ULL << REFCNT_BITS_OFFSET)
> +
> +#define DESC_FLAGS_SHORT_OFFSET (offsetof(struct vring_packed_desc, flags) / \
> + sizeof(uint16_t))
> +
> +#define DESC_FLAGS_SHORT_SIZE (sizeof(struct vring_packed_desc) / \
> + sizeof(uint16_t))
> +#define BATCH_FLAGS_MASK (1 << DESC_FLAGS_SHORT_OFFSET | \
> + 1 << (DESC_FLAGS_SHORT_OFFSET + DESC_FLAGS_SHORT_SIZE) | \
> + 1 << (DESC_FLAGS_SHORT_OFFSET + DESC_FLAGS_SHORT_SIZE * 2) | \
> + 1 << (DESC_FLAGS_SHORT_OFFSET + DESC_FLAGS_SHORT_SIZE * 3))
> +
> +#define FLAGS_BITS_OFFSET ((offsetof(struct vring_packed_desc, flags) - \
> + offsetof(struct vring_packed_desc, len)) * BYTE_SIZE)
> +
> +#define PACKED_FLAGS_MASK ((0ULL | VRING_DESC_F_AVAIL | VRING_DESC_F_USED) \
> + << FLAGS_BITS_OFFSET)
> +#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 DESC_FLAGS_POS 0xaa
> +#define MBUF_LENS_POS 0x6666
> +
> +int
> +vhost_reserve_avail_batch_packed_avx(struct virtio_net *dev,
> + struct vhost_virtqueue *vq,
> + struct rte_mempool *mbuf_pool,
> + struct rte_mbuf **pkts,
> + uint16_t avail_idx,
> + uintptr_t *desc_addrs,
> + uint16_t *ids)
> +{
> + struct vring_packed_desc *descs = vq->desc_packed;
> + uint32_t descs_status;
> + void *desc_addr;
> + uint16_t i;
> + uint8_t cmp_low, cmp_high, cmp_result;
> + uint64_t lens[PACKED_BATCH_SIZE];
> +
> + if (unlikely(avail_idx & PACKED_BATCH_MASK))
> + return -1;
> +
> + /* load 4 descs */
> + desc_addr = &vq->desc_packed[avail_idx];
> + __m512i desc_vec = _mm512_loadu_si512(desc_addr);
> +
> + /* burst check four status */
> + __m512i avail_flag_vec;
> + if (vq->avail_wrap_counter)
> +#if defined(RTE_ARCH_I686)
> + avail_flag_vec = _mm512_set4_epi64(PACKED_AVAIL_FLAG, 0x0,
> + PACKED_FLAGS_MASK, 0x0);
> +#else
> + avail_flag_vec = _mm512_maskz_set1_epi64(DESC_FLAGS_POS,
> + PACKED_AVAIL_FLAG);
> +
> +#endif
> + else
> +#if defined(RTE_ARCH_I686)
> + avail_flag_vec = _mm512_set4_epi64(PACKED_AVAIL_FLAG_WRAP,
> + 0x0, PACKED_AVAIL_FLAG_WRAP, 0x0);
> +#else
> + avail_flag_vec = _mm512_maskz_set1_epi64(DESC_FLAGS_POS,
> + PACKED_AVAIL_FLAG_WRAP);
> +#endif
> +
> + descs_status = _mm512_cmp_epu16_mask(desc_vec, avail_flag_vec,
> + _MM_CMPINT_NE);
> + if (descs_status & BATCH_FLAGS_MASK)
> + return -1;
> +
> + /* 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))
> + goto free_buf;
> +
> + desc_addrs[i] = addr_low +
> + dev->mem->regions[index].host_user_addr -
> + dev->mem->regions[index].guest_phys_addr;
> + lens[i] = descs[avail_idx + i].len;
> + rte_prefetch0((void *)(uintptr_t)desc_addrs[i]);
> +
> + pkts[i] = virtio_dev_pktmbuf_alloc(dev, mbuf_pool, lens[i]);
> + if (!pkts[i])
> + goto free_buf;
> + }
The above does not support vIOMMU, isn't it?
The more the packed datapath evolves, the more it gets optimized for a
very specific configuration.
In v19.11, indirect descriptors and chained buffers are handled as a
fallback. And now vIOMMU support is handled as a fallback.
I personnally don't like the path it is taking as it is adding a lot of
complexity on top of that.