On 3/7/2016 10:47 AM, Yuanhan Liu wrote:
> On Mon, Mar 07, 2016 at 02:32:46AM +0000, Xie, Huawei wrote:
>> On 3/4/2016 10:15 AM, Yuanhan Liu wrote:
>>> On Thu, Mar 03, 2016 at 04:30:42PM +0000, Xie, Huawei wrote:
>>>> On 2/18/2016 9:48 PM, Yuanhan Liu wrote:
>>>>> + mbuf_avail = 0;
>>>>> + mbuf_offset = 0;
>>>>> + while (desc_avail || (desc->flags & VRING_DESC_F_NEXT) != 0) {
>>>>> + /* This desc reachs to its end, get the next one */
>>>>> + if (desc_avail == 0) {
>>>>> + desc = &vq->desc[desc->next];
>>>>> +
>>>>> + desc_addr = gpa_to_vva(dev, desc->addr);
>>>>> + rte_prefetch0((void *)(uintptr_t)desc_addr);
>>>>> +
>>>>> + desc_offset = 0;
>>>>> + desc_avail = desc->len;
>>>>> +
>>>>> + PRINT_PACKET(dev, (uintptr_t)desc_addr, desc->len, 0);
>>>>> + }
>>>>> +
>>>>> + /*
>>>>> + * This mbuf reachs to its end, get a new one
>>>>> + * to hold more data.
>>>>> + */
>>>>> + if (mbuf_avail == 0) {
>>>>> + cur = rte_pktmbuf_alloc(mbuf_pool);
>>>>> + if (unlikely(!cur)) {
>>>>> + RTE_LOG(ERR, VHOST_DATA, "Failed to "
>>>>> + "allocate memory for mbuf.\n");
>>>>> + if (head)
>>>>> + rte_pktmbuf_free(head);
>>>>> + return NULL;
>>>>> + }
>>>> We could always allocate the head mbuf before the loop, then we save the
>>>> following branch and make the code more streamlined.
>>>> It reminds me that this change prevents the possibility of mbuf bulk
>>>> allocation, one solution is we pass the head mbuf from an additional
>>>> parameter.
>>> Yep, that's also something I have thought of.
>>>
>>>> Btw, put unlikely before the check of mbuf_avail and checks elsewhere.
>>> I don't think so. It would benifit for the small packets. What if,
>>> however, when TSO or jumbo frame is enabled that we have big packets?
>> Prefer to favor the path that packet could fit in one mbuf.
> Hmmm, why? While I know that TSO and mergeable buf is disable by default
> in our vhost example vhost-switch, they are enabled by default in real
> life.
mergable is only meaningful in RX path.
If you mean big packets in TX path, i personally favor the path that
packet fits in one mbuf.
>> Btw, not specially to this, return "m = copy_desc_to_mbuf(dev, vq,
>> desc_indexes[i], mbuf_pool)", failure case is unlikely to happen, so add
>> unlikely for the check if (m == NULL) there. Please check all branches
>> elsewhere.
> Thanks for the remind, will have a detail check.
>
> --yliu
>
