On 18.03.2016 13:47, Xie, Huawei wrote: > On 3/18/2016 6:39 PM, Ilya Maximets wrote: >> >> 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. > > What about the udpate to the used ring?
Next line is the only place where this vq->used->idx accessed. So, there must be no issues. >>>>>> vq->used->idx += entry_success; >>>>>> vhost_log_used_vring(dev, vq, offsetof(struct vring_used, idx), >>>>>> sizeof(vq->used->idx)); >>>>>> -- 2.5.0 >>>>> >>> >>> > > >
