[dpdk-dev] [PATCH RFC v3 1/3] vhost: use SMP barriers instead of compiler ones.

[Xie, Huawei]

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?


>
>>>>>  	vq->used->idx += entry_success;
>>>>>  	vhost_log_used_vring(dev, vq, offsetof(struct vring_used, idx),
>>>>>  			sizeof(vq->used->idx));
>>>>> -- 2.5.0
>>>>
>>
>>