On 18.03.2016 13:27, Xie, Huawei wrote: > On 3/18/2016 6:23 PM, Ilya Maximets wrote: >> On 18.03.2016 13:08, Xie, Huawei wrote: >>> On 2/24/2016 7:47 PM, Ilya Maximets wrote: >>>> * Wait until it's our turn to add our buffer >>>> @@ -979,7 +979,7 @@ rte_vhost_dequeue_burst(struct virtio_net *dev, >>>> uint16_t queue_id, >>>> entry_success++; >>>> } >>>> >>>> - rte_compiler_barrier(); >>>> + rte_smp_rmb(); >>> smp_rmb()? >> There is no such function 'smp_rmb' in DPDK. >> But: >> .../arch/arm/rte_atomic.h:#define rte_smp_rmb() rte_rmb() >> .../arch/ppc_64/rte_atomic.h:#define rte_smp_rmb() rte_compiler_barrier() >> .../arch/tile/rte_atomic.h:#define rte_smp_rmb() rte_compiler_barrier() >> .../arch/x86/rte_atomic.h:#define rte_smp_rmb() rte_compiler_barrier() > > I mean shoudn't be rte_smp_wmb()?
No. Here we need to be sure that copying of data from descriptor to our local mbuf completed before 'vq->used->idx += entry_success;'. Read memory barrier will help us with it. In other places write barriers used because copying performed in opposite direction. > >> >>>> vq->used->idx += entry_success; >>>> vhost_log_used_vring(dev, vq, offsetof(struct vring_used, idx), >>>> sizeof(vq->used->idx)); >>>> -- 2.5.0 >>> >>> > > >
