[dpdk-dev] ksoftirqd when using KNI

[dpdk-dev] ksoftirqd when using KNI

[Moon-Sang Lee]

I'm a newbie and testing DPDK KNI with 1G intel NIC.

According to my understanding of DPDK documents,
KNI should not raise interrupts when sending/receiving packets.

But when I transmit bunch of packets to my KNI ports,
'top command' shows ksoftirqd with 50% CPU load.

Would you give me some comments about this situation?



-- 
Moon-Sang Lee, SW Engineer
Email: sang0627@gmail.com
Wisdom begins in wonder. *Socrates*

Re: [dpdk-dev] ksoftirqd when using KNI

[Moon-Sang Lee]

I've observed CPU stats with top command, and found that ksoftirqd
is processing software interrupts which might come from dpdk-kni application
and would be processed by KNI and kernel net stack.

My observation shows that
1. dpdk-kni-application drops a half of rx packets (i.e. fail to deliver
packets to skb).
    this seems the rx_q is full in KNI side. I think this is because
processing in
    KNI and IP stack is much slow and receiving packets from device via
dpdk is
    much faster.
2. bonding multiple KNI interfaces to spread loads across multiple kernel
threads
    does not help reduce that processing time. In addition, packets are
transmitted
    out of order throughout multiple KNIs, which requires reordering
    at the communication end point.
3. NAT with native kernel performs twice better than that of KNI + native
kernel
    even though the latter does not incur hardware interrupts.

Anyway, my experiment was done in limited environment, so this does not
reflect
any general case.

My wish for simple NAT solution seems not feasible with KNI,
thus I should change my approach from KNI to pure dpdk application.




On Fri, Sep 18, 2015 at 8:53 PM, Moon-Sang Lee <sang0627@gmail.com> wrote:

>
> I'm a newbie and testing DPDK KNI with 1G intel NIC.
>
> According to my understanding of DPDK documents,
> KNI should not raise interrupts when sending/receiving packets.
>
> But when I transmit bunch of packets to my KNI ports,
> 'top command' shows ksoftirqd with 50% CPU load.
>
> Would you give me some comments about this situation?
>
>
>
> --
> Moon-Sang Lee, SW Engineer
> Email: sang0627@gmail.com
> Wisdom begins in wonder. *Socrates*
>



-- 
Moon-Sang Lee, SW Engineer
Email: sang0627@gmail.com
Wisdom begins in wonder. *Socrates*