Re: ixgbe vPMD RX functions and buffer number minimum requirement

[Zoltan Kiss <zoltan.kiss@linaro.org>]

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. 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.

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