[dpdk-dev] [RFC PATCH 02/13] add vhost packed ring fast enqueue function

[Jason Wang]

On 2019/7/11 下午5:37, Liu, Yong wrote:
>
>> -----Original Message-----
>> From: Jason Wang [mailto:jasowang at redhat.com]
>> Sent: Thursday, July 11, 2019 4:35 PM
>> To: Liu, Yong <yong.liu at intel.com>; Bie, Tiwei <tiwei.bie at intel.com>;
>> maxime.coquelin at redhat.com; dev at dpdk.org
>> Subject: Re: [dpdk-dev] [RFC PATCH 02/13] add vhost packed ring fast enqueue
>> function
>>
>>
>> On 2019/7/9 上午1:13, Marvin Liu wrote:
>>> In fast enqueue function, will first check whether descriptors are
>>> cache aligned. Fast enqueue function will check prerequisites in the
>>> beginning. Fast enqueue function do not support chained mbufs, normal
>>> function will handle that.
>>>
>>> Signed-off-by: Marvin Liu<yong.liu at intel.com>
>>>
>>> +	len = descs[avail_idx].len;
>>> +	len1 = descs[avail_idx + 1].len;
>>> +	len2 = descs[avail_idx + 2].len;
>>> +	len3 = descs[avail_idx + 3].len;
>>> +
>>> +	if (unlikely((pkts[0]->pkt_len > (len - buf_offset)) |
>>> +		(pkts[1]->pkt_len > (len1 - buf_offset)) |
>>> +		(pkts[2]->pkt_len > (len2 - buf_offset)) |
>>> +		(pkts[3]->pkt_len > (len3 - buf_offset))))
>>> +		return -1;
>>> +
>>> +	desc_addr = vhost_iova_to_vva(dev, vq,
>>> +			descs[avail_idx].addr,
>>> +			&len,
>>> +			VHOST_ACCESS_RW);
>>> +
>>> +	desc_addr1 = vhost_iova_to_vva(dev, vq,
>>> +			descs[avail_idx + 1].addr,
>>> +			&len1,
>>> +			VHOST_ACCESS_RW);
>>> +
>>> +	desc_addr2 = vhost_iova_to_vva(dev, vq,
>>> +			descs[avail_idx + 2].addr,
>>> +			&len2,
>>> +			VHOST_ACCESS_RW);
>>> +
>>> +	desc_addr3 = vhost_iova_to_vva(dev, vq,
>>> +			descs[avail_idx + 3].addr,
>>> +			&len3,
>>> +			VHOST_ACCESS_RW);
>>
>> How can you guarantee that len3 is zero after this?
>>
> Jason,
> Here just guarantee host mapped length of desc is same as value in desc.
> If value of len matched, data can be directly copied.
>
> If anything wrong in address conversion, value of len will be mismatched.
> This case will be handled by normal path.
>
> Thanks,
> Marvin


Right, I miss-read the code.

Thanks


>
>> Thanks