Re: [dpdk-dev] ixgbe TX function selection

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

On 04/03/16 01:47, Lu, Wenzhuo 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
> Thanks for let us know the problem. But I don't catch your point. Do you really mean TX here? After a quick look at the code, I don’t find the SG/non-SG functions for TX. Do I miss something?

The simple code path doesn't handle multisegmented packets. 
ixgbe_txq_vec_setup() and ixgbe_xmit_pkts_simple() doesn't even check 
the next pointer of the mbuf, just put the first one on the descriptor 
ring, and when TX completion happens, the memory is leaked because it 
just sets ->next to NULL, and calls rte_mempool_put[_bulk]
ixgbe_xmit_pkts() puts all the segments on the descriptor ring, 
therefore when the descriptors are released they are released as well.
This is what these functions supposed to do, but my point is it's very 
easy to send a multisegmented packet to the simple code path.


>
>> (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.
> Which one will cause problem? SG or non-SG packets? And where does the memory leak happen?
>
>> 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.
>>
>> Regards,
>>
>> Zoltan