Re: [dpdk-dev] ixgbe TX function selection

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

On 18/03/16 00:45, Lu, Wenzhuo wrote:
> Hi Zoltan,
>
>
>> -----Original Message-----
>> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Zoltan Kiss
>> Sent: Friday, March 18, 2016 1:11 AM
>> To: Wu, Jingjing; dev@dpdk.org
>> Subject: Re: [dpdk-dev] ixgbe TX function selection
>>
>>
>>
>> On 10/03/16 07:51, Wu, Jingjing wrote:
>>> Hi, Zoltan
>>>
>>>> -----Original Message-----
>>>> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Zoltan Kiss
>>>> Sent: Wednesday, March 2, 2016 3:19 AM
>>>> To: dev@dpdk.org
>>>> Subject: [dpdk-dev] ixgbe TX function selection
>>>>
>>>> Hi,
>>>>
>>>> I've noticed that ixgbe_set_tx_function() selects the non-SG function
>>>> even if (dev->data->scattered_rx == 1). That seems a bit dangerous,
>>>> as you can turn that on inadvertently when you don't set
>>>> max_rx_pkt_len and buffer size in certain ways. I've learnt it in the
>>>> hard way, as my segmented packets were leaking memory on the TX path,
>>>> which doesn't cries if you send out segmented packets.
>>>> How should this case be treated? Assert on the non-SG TX side for the
>>>> 'next' pointer? Or turning on SG if RX has it? It doesn't seem to be
>>>> a solid way as other interfaces still can have SG turned on.
>>>>
>>>
>>> If you look into the ixgbe_set_tx_function, you will find tx function
>>> selection is decided by the tx_flags on queue configure, which is
>>> passed by rte_eth_txconf. So even you set dev->data->scattered_rx to
>>> 1, if the tx_flags is ETH_TXQ_FLAGS_NOMULTSEGS, ixgbe_xmit_pkts_simple
>>> is still selected as tx function. So, you'd better to set tx_flags=0, and have a try.
>>
>> You mean getting default_txconf from rte_eth_dev_info_get() and explicitly turn
>> ETH_TXQ_FLAGS_NOMULTSEGS to 0? (filling tx_flags with zeros doesn't work
>> very well) That's a way to solve it for me, but I'm rather talking about using
>> defaults which doesn't cause memory leak quite easily.
> Yes, ETH_TXQ_FLAGS_NOMULTSEGS only can be set to 1 when you know all your packets will not be segmented.
> I think that means normally we should use full function path for TX, for we have no knowledge about if the packets will be segmented or not.
> You don't need to set tx_flags to 0, only the ETH_TXQ_FLAGS_NOMULTSEGS bit should be 0, the other bits can be 1 if needed.

So can we agree that the default settings should set 
ETH_TXQ_FLAGS_NOMULTSEGS to 0?


>
>>
>>>
>>>> Regards,
>>>>
>>>> Zoltan