Re: Newbie questions

[Jesper Dangaard Brouer <brouer@redhat.com>]

On Fri, 18 Jun 2021 13:31:06 -0300
"Ethy H. Brito" <ethy.brito@inexo.com.br> wrote:

> Hi All.
> 
> I've been doing some home work reading the docs and some doubts have raised.
> For reference, my environment is 
> 	Ubuntu 20.04
> 	kernel 5.4.0-66 
> 	tc utility, iproute2-ss200127.
> 
> 1) https://xdp-project.net/areas/cpumap.html#cpumap--Create-script-MQ-HTB-silo-setup says that: 
> 	"XPS (Transmit Packet Steering) will take precedence over any changes to 
> 	skb->queue_mapping. You need to disable *XDP* via mask=00 in files 
> 	/sys/class/net/DEV/queues/tx-*/xps_cpus"
> 
> Shouldn't it say I need to disable *XPS* (not XDP) using mask=00??

You are absolutely right it is a typo. Can I ask you to fix that and
send a GitHub PR?

The file you need to change is:
 https://github.com/xdp-project/xdp-project/blob/master/areas/cpumap.org

 
> 2) Taking tc_mq_htb_setup_example.sh as reference, how to enable XDP?

XDP gets enabled when you load an XDP program.

> Since I have to disable XPS, I assume I have to enable something in
> replacement, right?

No, XPS is just a kernel feature you need to disable, because it
conflicts with the TC-BPF program usage of skb->queue_mapping.


> How to set that CPU-0 will deal with mq queue 7FFF:1, CPU-1 will deal
> with 7FFF:2, and so on?

That is the role of the XDP program that redirect into a cpumap, and
the key in the cpumap is the CPU number.

 
> 3) Is XDP available in kernel 5.4.0 ?

I think so.

The real question is what NIC card drivers are you using?


> 4) Is XPS a suitable "substitute" for XDP ?

XPS and XDP are completely unrelated kernel features.

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer