[dpdk-users] high jitter in dpdk kni

Andriy Berestovskyy aber at semihalf.com
Mon Jan 25 14:43:03 CET 2016

Hi Masoud,
Try a low latency kernel (i.e. linux-image-lowlatency).


On Mon, Jan 25, 2016 at 2:15 PM, Masoud Moshref Javadi
<masood.moshref.j at gmail.com> wrote:
> I see. But this should not be the issue in Ping.
> By the way, I checked the timestamps of sending and receiving times at the
> kni sample application (kni_ingress and kni_egress methods). The RTT at
> that level is OK (0.1ms) and it seems the jitter comes from the kni kernel
> module.
> On Mon, Jan 25, 2016 at 12:29 AM Freynet, Marc (Nokia - FR) <
> marc.freynet at nokia.com> wrote:
>> Hi,
>> Some months ago we had a problem with the KNI driver.
>> Our DPDK application forwards to the Linux kernel through KNI the SCTP PDU
>> received from the Eth NIC.
>> In one configuration, the SCTP port Source and Destination were constant
>> on all SCTP connections.
>> This is a known SCTP issue as in the multi processor environment, the SCTP
>> stack uses the port Source and Destination to hash the processor that will
>> run the SCTP context in the kernel.
>> SCTP cannot use the IP address as a hash key thanks to the SCTP multi
>> homing feature.
>> As all SCTP PDU on all SCTP connections where processed by the same Core,
>> this creates a bottle neck and the KNI interface starts creating Jitter and
>> even was losing PDU when sending the SCTP PDU to the IP Linux kernel stack.
>> I am wondering if in a previous release it you not be possible to add KNI
>> a kind of load sharing with different queues on different cores to forward
>> the received PDU to the IP Linux stack.
>> "Bowl of rice will raise a benefactor, a bucket of rice will raise a
>> enemy.", Chinese proverb.
>> Alcatel-Lucent France
>> Centre de Villarceaux
>> Route de Villejust
>> 91620 NOZAY France
>> Tel:  +33 (0)1 6040 1960
>> Intranet: 2103 1960
>> marc.freynet at nokia.com
>> -----Original Message-----
>> From: users [mailto:users-bounces at dpdk.org] On Behalf Of EXT Masoud
>> Moshref Javadi
>> Sent: samedi 23 janvier 2016 15:18
>> To: users at dpdk.org
>> Subject: [dpdk-users] high jitter in dpdk kni
>> I see jitter in KNI RTT. I have two servers. I run kni sample application
>> on one, configure its IP and ping an external interface.
>> sudo -E build/kni -c 0xaaaa -n 4 -- -p 0x1 -P --config="(0,3,5)"
>> sudo ifconfig vEth0
>> ping
>> This is the ping result:
>> 64 bytes from icmp_seq=5 ttl=64 time=1.93 ms
>> 64 bytes from icmp_seq=6 ttl=64 time=0.907 ms
>> 64 bytes from icmp_seq=7 ttl=64 time=3.15 ms
>> 64 bytes from icmp_seq=8 ttl=64 time=1.96 ms
>> 64 bytes from icmp_seq=9 ttl=64 time=3.95 ms
>> 64 bytes from icmp_seq=10 ttl=64 time=2.90 ms
>> 64 bytes from icmp_seq=11 ttl=64 time=0.933 ms
>> The ping delay between two servers without kni is 0.170ms.
>> I'm using dpdk 2.2.
>> Any thought on how to keep KNI delay predictable?
>> Thanks

Andriy Berestovskyy

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