netdev - Re: [RFC PATCHv2 bpf-next 1/2] xdp: add a new helper for dev map multicast support

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Date:   Fri, 8 May 2020 16:53:57 +0800
From:   Hangbin Liu <liuhangbin@...il.com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org,
        Jiri Benc <jbenc@...hat.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Eelco Chaudron <echaudro@...hat.com>, ast@...nel.org,
        Daniel Borkmann <daniel@...earbox.net>,
        Lorenzo Bianconi <lorenzo.bianconi@...hat.com>
Subject: Re: [RFC PATCHv2 bpf-next 1/2] xdp: add a new helper for dev map
 multicast support

On Wed, May 06, 2020 at 12:00:08PM +0200, Toke Høiland-Jørgensen wrote:
> > No, I haven't test the performance. Do you have any suggestions about how
> > to test it? I'd like to try forwarding pkts to 10+ ports. But I don't know
> > how to test the throughput. I don't think netperf or iperf supports
> > this.
> 
> What I usually do when benchmarking XDP_REDIRECT is to just use pktgen
> (samples/pktgen in the kernel source tree) on another machine,
> specifically, like this:
> 
> ./pktgen_sample03_burst_single_flow.sh  -i enp1s0f1 -d 10.70.2.2 -m ec:0d:9a:db:11:35 -t 4  -s 64
> 
> (adjust iface, IP and MAC address to your system, of course). That'll
> flood the target machine with small UDP packets. On that machine, I then
> run the 'xdp_redirect_map' program from samples/bpf. The bpf program
> used by that sample will update an internal counter for every packet,
> and the userspace prints it out, which gives you the performance (in
> PPS). So just modifying that sample to using your new multicast helper
> (and comparing it to regular REDIRECT to a single device) would be a
> first approximation of a performance test.

Thanks for this method. I will update the sample and do some more tests.
> 
> You could do something like:
> 
> bool first = true;
> for (;;) {
> 
> [...]
> 
>            if (!first) {
>    		nxdpf = xdpf_clone(xdpf);
>    		if (unlikely(!nxdpf))
>    			return -ENOMEM;
>    		bq_enqueue(dev, nxdpf, dev_rx);
>            } else {
>    		bq_enqueue(dev, xdpf, dev_rx);
>    		first = false;
>            }
> }
> 
> /* didn't find anywhere to forward to, free buf */
> if (first)
>    xdp_return_frame_rx_napi(xdpf);

I think the first xdpf will be consumed by the driver and the later
xdpf_clone() will failed, won't it?

How about just do a xdp_return_frame_rx_napi(xdpf) after all nxdpf enqueue?

> > @@ -3534,6 +3539,8 @@ int xdp_do_redirect(struct net_device *dev, struct
> > xdp_buff *xdp,
> >                   struct bpf_prog *xdp_prog)
> >  {
> >       struct bpf_redirect_info *ri = this_cpu_ptr(&bpf_redirect_info);
> > +     bool exclude_ingress = !!(ri->flags & BPF_F_EXCLUDE_INGRESS);
> > +     struct bpf_map *ex_map = READ_ONCE(ri->ex_map);
>
> I don't think you need the READ_ONCE here since there's already one
> below?

BTW, I forgot to ask, why we don't need the READ_ONCE for ex_map?
I though the map and ex_map are two different pointers.

> >       struct bpf_map *map = READ_ONCE(ri->map);

Thanks
Hangbin