Hi Yinan, Thanks for verification and reporting this, I will dump the assembly code and make an analysis after I am back from travel. >From my understanding the assembly code for x86 should be same, but I am not >sure if anything we were missing.
Is this <1 perf drop coming from run to run variances, or system noise? /Gavin > -----Original Message----- > From: Wang, Yinan <yinan.w...@intel.com> > Sent: Wednesday, September 18, 2019 7:21 AM > To: Joyce Kong (Arm Technology China) <joyce.k...@arm.com>; > dev@dpdk.org > Cc: nd <n...@arm.com>; maxime.coque...@redhat.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 Nagarahalli > <honnappa.nagaraha...@arm.com>; Gavin Hu (Arm Technology China) > <gavin...@arm.com> > Subject: RE: [PATCH v4 2/2] virtio: one way barrier for packed vring desc used > flags > > > 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
