[dpdk-dev] [PATCH v2] kni: add new mbuf in alloc_q only based on its empty slots
gowrishankar.m at linux.vnet.ibm.com
Thu Jun 1 07:56:14 CEST 2017
On Wednesday 31 May 2017 09:51 PM, Ferruh Yigit wrote:
> I have sampled below data in x86_64 for KNI on ixgbe pmd. iperf server
>> runs on
>> remote interface connecting PMD and iperf client runs on KNI interface,
>> so as to
>> create more egress from KNI into DPDK (w/o and with this patch) for 1MB and
>> 100MB data. rx and tx stats are from kni app (USR1).
>> 100MB w/o patch 1.28Gbps
>> rx tx alloc_call alloc_call_mt1tx freembuf_call
>> 3933 72464 51042 42472 1560540
> Some math:
> alloc called 51042 times with allocating 32 mbufs each time,
> 51042 * 32 = 1633344
> freed mbufs: 1560540
> used mbufs: 1633344 - 1560540 = 72804
> 72804 =~ 72464, so looks correct.
> Which means rte_kni_rx_burst() called 51042 times and 72464 buffers
> As you already mentioned, for each call kernel able to put only 1-2
> packets into the fifo. This number is close to 3 for my test with KNI PMD.
> And for this case, agree your patch looks reasonable.
> But what if kni has more egress traffic, that able to put >= 32 packets
> between each rte_kni_rx_burst()?
> For that case this patch introduces extra cost to get allocq_free count.
Are there case(s) we see kernel thread writing txq faster at a rate
higher than kni application
could dequeue it ?. In my understanding, KNI is suppose to be a slow
path as it puts
packets back into network stack (control plane ?).
> Overall I am not disagree with patch, but I have concern if this would
> cause performance loss some cases while making better for this one. That
> would help a lot if KNI users test and comment.
> For me, applying patch didn't give any difference in final performance
> numbers, but if there is no objection, I am OK to get this patch.
More information about the dev