[dpdk-dev] [PATCH v2 15/16] vhost: check whether disable software pre-fetch

[Marvin Liu]

Disable software pre-fetch actions on Skylake and Cascadelake platforms.
Hardware can fetch needed data for vhost, additional software pre-fetch
will have impact on performance.

Signed-off-by: Marvin Liu <yong....@intel.com>

diff --git a/lib/librte_vhost/Makefile b/lib/librte_vhost/Makefile
index 30839a001..5f3b42e56 100644
--- a/lib/librte_vhost/Makefile
+++ b/lib/librte_vhost/Makefile
@@ -16,6 +16,12 @@ CFLAGS += -I vhost_user
 CFLAGS += -fno-strict-aliasing
 LDLIBS += -lpthread
 
+AVX512_SUPPORT=$(shell $(CC) -march=native -dM -E - </dev/null |grep AVX512F)
+
+ifneq ($(AVX512_SUPPORT),)
+CFLAGS += -DDISABLE_SWPREFETCH
+endif
+
 ifeq ($(RTE_TOOLCHAIN), gcc)
 ifeq ($(shell test $(GCC_VERSION) -ge 83 && echo 1), 1)
 CFLAGS += -DSUPPORT_GCC_UNROLL_PRAGMA
diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c
index 066514e43..357517cdd 100644
--- a/lib/librte_vhost/virtio_net.c
+++ b/lib/librte_vhost/virtio_net.c
@@ -478,7 +478,9 @@ map_one_desc(struct virtio_net *dev, struct vhost_virtqueue 
*vq,
                if (unlikely(!desc_addr))
                        return -1;
 
+#ifndef DISABLE_SWPREFETCH
                rte_prefetch0((void *)(uintptr_t)desc_addr);
+#endif
 
                buf_vec[vec_id].buf_iova = desc_iova;
                buf_vec[vec_id].buf_addr = desc_addr;
@@ -999,7 +1001,9 @@ virtio_dev_rx_split(struct virtio_net *dev, struct 
vhost_virtqueue *vq,
         */
        rte_smp_rmb();
 
+#ifndef DISABLE_SWPREFETCH
        rte_prefetch0(&vq->avail->ring[vq->last_avail_idx & (vq->size - 1)]);
+#endif
 
        for (pkt_idx = 0; pkt_idx < count; pkt_idx++) {
                uint32_t pkt_len = pkts[pkt_idx]->pkt_len + dev->vhost_hlen;
@@ -1093,7 +1097,9 @@ virtio_dev_rx_burst_packed(struct virtio_net *dev, struct 
vhost_virtqueue *vq,
 
        UNROLL_PRAGMA(PRAGMA_PARAM)
        for (i = 0; i < PACKED_DESCS_BURST; i++) {
+#ifndef DISABLE_SWPREFETCH
                rte_prefetch0((void *)(uintptr_t)desc_addrs[i]);
+#endif
                hdrs[i] = (struct virtio_net_hdr_mrg_rxbuf *)desc_addrs[i];
                lens[i] = pkts[i]->pkt_len + dev->vhost_hlen;
        }
@@ -1647,7 +1653,9 @@ virtio_dev_tx_split(struct virtio_net *dev, struct 
vhost_virtqueue *vq,
         */
        rte_smp_rmb();
 
+#ifndef DISABLE_SWPREFETCH
        rte_prefetch0(&vq->avail->ring[vq->last_avail_idx & (vq->size - 1)]);
+#endif
 
        VHOST_LOG_DEBUG(VHOST_DATA, "(%d) %s\n", dev->vid, __func__);
 
@@ -1818,7 +1826,9 @@ virtio_dev_tx_burst_packed(struct virtio_net *dev, struct 
vhost_virtqueue *vq,
 
        UNROLL_PRAGMA(PRAGMA_PARAM)
        for (i = 0; i < PACKED_DESCS_BURST; i++) {
+#ifndef DISABLE_SWPREFETCH
                rte_prefetch0((void *)(uintptr_t)desc_addrs[i]);
+#endif
                rte_memcpy(rte_pktmbuf_mtod_offset(pkts[i], void *, 0),
                           (void *)(uintptr_t)(desc_addrs[i] + buf_offset),
                           pkts[i]->pkt_len);
-- 
2.17.1