Hi Joyce,
I test performance impact of your patch set with code base commit id: d03d8622db48918d14bfe805641b1766ecc40088, after applying your v4 patch set , packed ring shows small performance drop as below: PVP vhost/virtio 1c1q test commit:d03d8622db48918 apply v4 patch set pvp_virtio11_mergeable 7.218 7.147 pvp_virtio11_normal 7.217 7.182 Thanks, Yinan > -----Original Message----- > From: Joyce Kong [mailto:joyce.k...@arm.com] > Sent: 2019年9月17日 13:28 > To: dev@dpdk.org > Cc: n...@arm.com; maxime.coque...@redhat.com; Wang, Yinan > <yinan.w...@intel.com>; Richardson, Bruce <bruce.richard...@intel.com>; Bie, > Tiwei <tiwei....@intel.com>; Wang, Zhihong <zhihong.w...@intel.com>; > amore...@redhat.com; Wang, Xiao W <xiao.w.w...@intel.com>; Liu, Yong > <yong....@intel.com>; jfreim...@redhat.com; honnappa.nagaraha...@arm.com; > gavin...@arm.com > Subject: [PATCH v4 2/2] virtio: one way barrier for packed vring desc used > flags > > In case VIRTIO_F_ORDER_PLATFORM(36) is not negotiated, then the frontend > and backend are assumed to be implemented in software, that is they can run on > identical CPUs in an SMP configuration. > Thus a weak form of memory barriers like rte_smp_r/wmb, other than > rte_cio_r/wmb, is sufficient for this case(vq->hw->weak_barriers == 1) and > yields better performance. > For the above case, this patch helps yielding even better performance by > replacing the two-way barriers with C11 one-way barriers for used flags in > packed > ring. > > Signed-off-by: Joyce Kong <joyce.k...@arm.com> > Reviewed-by: Gavin Hu <gavin...@arm.com> > Reviewed-by: Phil Yang <phil.y...@arm.com> > Reviewed-by: Maxime Coquelin <maxime.coque...@redhat.com> > --- > drivers/net/virtio/virtio_rxtx.c | 12 +++++++--- > drivers/net/virtio/virtio_user/virtio_user_dev.c | 4 ++-- > drivers/net/virtio/virtqueue.h | 28 > +++++++++++++++++++++++- > lib/librte_vhost/virtio_net.c | 5 ++--- > 4 files changed, 40 insertions(+), 9 deletions(-) > > diff --git a/drivers/net/virtio/virtio_rxtx.c > b/drivers/net/virtio/virtio_rxtx.c > index a87ffe1..2f0879c 100644 > --- a/drivers/net/virtio/virtio_rxtx.c > +++ b/drivers/net/virtio/virtio_rxtx.c > @@ -122,9 +122,11 @@ virtqueue_dequeue_burst_rx_packed(struct virtqueue > *vq, > > for (i = 0; i < num; i++) { > used_idx = vq->vq_used_cons_idx; > + /* desc_is_used has a load-acquire or rte_cio_rmb inside > + * and wait for used desc in virtqueue. > + */ > if (!desc_is_used(&desc[used_idx], vq)) > return i; > - virtio_rmb(vq->hw->weak_barriers); > len[i] = desc[used_idx].len; > id = desc[used_idx].id; > cookie = (struct rte_mbuf *)vq->vq_descx[id].cookie; @@ -233,8 > +235,10 @@ virtio_xmit_cleanup_inorder_packed(struct virtqueue *vq, int num) > struct vq_desc_extra *dxp; > > used_idx = vq->vq_used_cons_idx; > + /* desc_is_used has a load-acquire or rte_cio_rmb inside > + * and wait for used desc in virtqueue. > + */ > while (num > 0 && desc_is_used(&desc[used_idx], vq)) { > - virtio_rmb(vq->hw->weak_barriers); > id = desc[used_idx].id; > do { > curr_id = used_idx; > @@ -265,8 +269,10 @@ virtio_xmit_cleanup_normal_packed(struct virtqueue > *vq, int num) > struct vq_desc_extra *dxp; > > used_idx = vq->vq_used_cons_idx; > + /* desc_is_used has a load-acquire or rte_cio_rmb inside > + * and wait for used desc in virtqueue. > + */ > while (num-- && desc_is_used(&desc[used_idx], vq)) { > - virtio_rmb(vq->hw->weak_barriers); > id = desc[used_idx].id; > dxp = &vq->vq_descx[id]; > vq->vq_used_cons_idx += dxp->ndescs; > diff --git a/drivers/net/virtio/virtio_user/virtio_user_dev.c > b/drivers/net/virtio/virtio_user/virtio_user_dev.c > index 7911c39..1c575d0 100644 > --- a/drivers/net/virtio/virtio_user/virtio_user_dev.c > +++ b/drivers/net/virtio/virtio_user/virtio_user_dev.c > @@ -698,8 +698,8 @@ virtio_user_handle_cq_packed(struct virtio_user_dev > *dev, uint16_t queue_idx) > if (vq->used_wrap_counter) > flags |= VRING_PACKED_DESC_F_AVAIL_USED; > > - rte_smp_wmb(); > - vring->desc[vq->used_idx].flags = flags; > + __atomic_store_n(&vring->desc[vq->used_idx].flags, flags, > + __ATOMIC_RELEASE); > > vq->used_idx += n_descs; > if (vq->used_idx >= dev->queue_size) { diff --git > a/drivers/net/virtio/virtqueue.h b/drivers/net/virtio/virtqueue.h index > b728ff8..8d7f197 100644 > --- a/drivers/net/virtio/virtqueue.h > +++ b/drivers/net/virtio/virtqueue.h > @@ -54,6 +54,32 @@ virtio_wmb(uint8_t weak_barriers) > rte_cio_wmb(); > } > > +static inline uint16_t > +virtqueue_fetch_flags_packed(struct vring_packed_desc *dp, > + uint8_t weak_barriers) > +{ > + uint16_t flags; > + > + if (weak_barriers) { > +/* x86 prefers to using rte_smp_rmb over __atomic_load_n as it reports > + * a better perf(~1.5%), which comes from the saved branch by the compiler. > + * The if and else branch are identical with the smp and cio barriers > +both > + * defined as compiler barriers on x86. > + */ > +#ifdef RTE_ARCH_X86_64 > + flags = dp->flags; > + rte_smp_rmb(); > +#else > + flags = __atomic_load_n(&dp->flags, __ATOMIC_ACQUIRE); #endif > + } else { > + flags = dp->flags; > + rte_cio_rmb(); > + } > + > + return flags; > +} > + > static inline void > virtqueue_store_flags_packed(struct vring_packed_desc *dp, > uint16_t flags, uint8_t weak_barriers) @@ -307,7 > +333,7 > @@ desc_is_used(struct vring_packed_desc *desc, struct virtqueue *vq) { > uint16_t used, avail, flags; > > - flags = desc->flags; > + flags = virtqueue_fetch_flags_packed(desc, vq->hw->weak_barriers); > used = !!(flags & VRING_PACKED_DESC_F_USED); > avail = !!(flags & VRING_PACKED_DESC_F_AVAIL); > > diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c > index > e7463ff..241d467 100644 > --- a/lib/librte_vhost/virtio_net.c > +++ b/lib/librte_vhost/virtio_net.c > @@ -110,8 +110,6 @@ flush_shadow_used_ring_packed(struct virtio_net *dev, > used_idx -= vq->size; > } > > - rte_smp_wmb(); > - > for (i = 0; i < vq->shadow_used_idx; i++) { > uint16_t flags; > > @@ -147,7 +145,8 @@ flush_shadow_used_ring_packed(struct virtio_net *dev, > } > } > > - vq->desc_packed[head_idx].flags = head_flags; > + __atomic_store_n(&vq->desc_packed[head_idx].flags, head_flags, > + __ATOMIC_RELEASE); > > vhost_log_cache_used_vring(dev, vq, > head_idx * > -- > 2.7.4
