Re: [dpdk-dev] ixgbe vPMD RX functions and buffer number minimum requirement

["Liang, Cunming" <cunming.liang@intel.com>]

Hi,

On 7/28/2015 8:10 AM, Ananyev, Konstantin wrote:
> Hi Zoltan,
>
>> -----Original Message-----
>> From: Zoltan Kiss [mailto:zoltan.kiss@linaro.org]
>> Sent: Monday, July 27, 2015 12:38 PM
>> To: Ananyev, Konstantin; Richardson, Bruce; dev@dpdk.org
>> Subject: Re: [dpdk-dev] ixgbe vPMD RX functions and buffer number minimum requirement
>>
>> Hi Konstantin,
>>
>> Thanks! Another question I would have: why does _recv_raw_pkts_vec()
>> insist on (nb_pkts > RTE_IXGBE_VPMD_RX_BURST)? Looking at the code it
>> should be able to return packets when nb_pkts >=
>> RTE_IXGBE_DESCS_PER_LOOP.
> Yes, that seems pretty trivial modification.
> Don't know any good reason why it wasn't done that way.
It's true, looks too strict condition check. I tend to set "nb_pkts = 
RTE_ALIGN_FLOOR(nb_pkts, RTE_IXGBE_DESCS_PER_LOOP)" instead.
And do loop in "pos < nb_pkts" manner.
>
>> The split_flags check in
>> ixgbe_recv_scattered_pkts_vec() would be a bit more complicated, and
>> therefore maybe would have a tiny performance overhead as well, but I
>> don't it would be anything serious.
> I think, if the performance wouldn't be affected, that will be really useful change.
> So it is definitely worth to try.
> Probably even _recv_raw_pkts_vec() for first nb_pkts &  ~(RTE_IXGBE_VPMD_RX_BURST - 1),
> and then sort of scalar analog for the remainder.
> Konstantin
>
>> Regards,
>>
>> Zoltan
>>
>>
>> On 24/07/15 17:43, Ananyev, Konstantin wrote:
>>> Hi Zoltan,
>>>
>>>> -----Original Message-----
>>>> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Zoltan Kiss
>>>> Sent: Friday, July 24, 2015 4:00 PM
>>>> To: Richardson, Bruce; dev@dpdk.org
>>>> Subject: [dpdk-dev] ixgbe vPMD RX functions and buffer number minimum requirement
>>>>
>>>> Hi,
>>>>
>>>> I was thinking how to handle the situation when you call
>>>> rte_eth_rx_burst with less than RTE_IXGBE_VPMD_RX_BURST buffers. In
>>>> ODP-DPDK unfortunately we can't force this requirement onto the calling
>>>> application.
>>>> One idea I had to check in ixgbe_recv_pkts_vec() if nb_pkts <
>>>> RTE_IXGBE_VPMD_RX_BURST, and call ixgbe_recv_pkts_bulk_alloc in that
>>>> case. Accordingly, in ixgbe_recv_scattered_pkts_vec() we could call
>>>> ixgbe_recv_scattered_pkts() in this case. A branch predictor can easily
>>>> eliminate the performance penalty of this, and applications can use
>>>> whatever burst size feasible for them.
>>>> The obvious problem could be whether you can mix the receive functions
>>>> this way. I have a feeling it wouldn't fly, but I wanted to ask first
>>>> before spending time investigate this option further.
>>> No, it is not possible to mix different RX functions, they setup/use ixgbe_rx_queue
>>> fields in a different manner.
>>> Konstantin
>>>
>>>> Regards,
>>>>
>>>> Zoltan