Re: CPU redirect and skb mode

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

On Thu, 04 Jan 2018 01:18:29 +0100 Eric Leblond <eric@regit.org> wrote:

> Hello,
> 
> I'm currently working on implementing XDP CPU redirect map inside
> Suricata.
> 
> I've used CPU redirect map on my test laptop that has only skb mode
> available and my implementation was failing with result being almost
> all packets if not all were dropped.

Remember that the tool xdp_monitor helps identify if XDP drops packets.
(It's on my TODO list to expose the return values, until now I've just
used the existing perf record/script to inspect the individual return
ERRNO's when I needed more details).

Maybe suricata should attach itself to the XDP error tracepoints, to
help the user experience?

> So I decided to build the XPD sample and test them:
> 
> sudo ./xdp_redirect_cpu --debug -d wlan0  --cpu 4 -S

I notice the -S option, which long option is --skb-mode.

> The result was the same with packet blocked.
> 
> Am I missing something in the setup ?

The cpumap redirect feature does not for for skb-mode. 

It's on my TODO-list to make it work for skb-mode, but I got
side-tracked after netconf (implementing xdp_rxq_info).  From a
performance PoV it goes against the basic idea of CPUMAP, which is to
move the SKB allocation to another CPU.  But for completeness sake I
will implement this, it just requires the cpumap-code handle both
xdp_buff's and SKB's in its queue.

> For those interested, I've pushed my POC implementation here: 
> https://github.com/regit/suricata/commit/b1369fd0dc3a22a932190846a8bcbec4bfbd34b2

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