[dpdk-dev] [PATCH RFC v3 1/3] vhost: use SMP barriers instead of compiler ones.
Ilya Maximets
i.maximets at samsung.com
Fri Mar 18 11:39:13 CET 2016
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
>>>
>>>
>
>
>
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