Re: [PATCHv4 bpf-next 0/2] xdp: add dev map multicast support

On Wed, 27 May 2020 17:04:50 +0200
Toke Høiland-Jørgensen [off-list ref] wrote:

Hangbin Liu [off-list ref] writes:

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On Wed, May 27, 2020 at 12:21:54PM +0200, Toke Høiland-Jørgensen wrote:  

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The example in patch 2 is functional, but not a lot of effort
has been made on performance optimisation. I did a simple test(pkt size 64)
with pktgen. Here is the test result with BPF_MAP_TYPE_DEVMAP_HASH
arrays:

bpf_redirect_map() with 1 ingress, 1 egress:
generic path: ~1600k pps
native path: ~980k pps

bpf_redirect_map_multi() with 1 ingress, 3 egress:
generic path: ~600k pps
native path: ~480k pps

bpf_redirect_map_multi() with 1 ingress, 9 egress:
generic path: ~125k pps
native path: ~100k pps

The bpf_redirect_map_multi() is slower than bpf_redirect_map() as we loop
the arrays and do clone skb/xdpf. The native path is slower than generic
path as we send skbs by pktgen. So the result looks reasonable.  

How are you running these tests? Still on virtual devices? We really  

I run it with the test topology in patch 2/2. The test is run on physical
machines, but I use veth interface. Do you mean use a physical NIC driver
for testing?  

Yes, sorry, when I said 'physical machine' I should have also 'physical
NIC'. We really need to know how the performance of this is on the XDP
fast path, i.e., when there are no skbs involved at all.

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BTW, when using pktgen, I got an panic because the skb don't have enough
header room. The code path looks like

do_xdp_generic()
  - netif_receive_generic_xdp()
    - skb_headroom(skb) < XDP_PACKET_HEADROOM
      - pskb_expand_head()
        - BUG_ON(skb_shared(skb))

So I added a draft patch for pktgen, not sure if it has any influence.  

Hmm, as Jesper said pktgen was really not intended to be used this way,
so I guess that's why. I guess I'll let him comment on whether he thinks
it's worth fixing; or you could send this as a proper patch and see if
anyone complains about it ;)

Don't use pktgen in this way with veth.  If anything pktgen should
detect that you use pktgen in virtual interfaces and reject/disallow
that you do this.

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