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

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Message-ID: <87d06ees41.fsf@toke.dk>
Date:   Thu, 04 Jun 2020 18:02:54 +0200
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Hangbin Liu <liuhangbin@...il.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: [PATCHv4 bpf-next 0/2] xdp: add dev map multicast support

Hangbin Liu <liuhangbin@...il.com> writes:

> On Thu, Jun 04, 2020 at 02:37:23PM +0200, Toke HÃƒÂ¸iland-JÃƒÂ¸rgensen wrote:
>> > Now I use the ethtool_stats.pl to count forwarding speed and here is the result:
>> >
>> > With kernel 5.7(ingress i40e, egress i40e)
>> > XDP:
>> > bridge: 1.8M PPS
>> > xdp_redirect_map:
>> >   generic mode: 1.9M PPS
>> >   driver mode: 10.4M PPS
>> 
>> Ah, now we're getting somewhere! :)
>> 
>> > Kernel 5.7 + my patch(ingress i40e, egress i40e)
>> > bridge: 1.8M
>> > xdp_redirect_map:
>> >   generic mode: 1.86M PPS
>> >   driver mode: 10.17M PPS
>> 
>> Right, so this corresponds to a ~2ns overhead (10**9/10400000 -
>> 10**9/10170000). This is not too far from being in the noise, I suppose;
>> is the difference consistent?
>
> Sorry, I didn't get, what different consistent do you mean?

I meant, how much do the numbers vary between each test run?

>> > xdp_redirect_map_multi:
>> >   generic mode: 1.53M PPS
>> >   driver mode: 7.22M PPS
>> >
>> > Kernel 5.7 + my patch(ingress i40e, egress veth)
>> > xdp_redirect_map:
>> >   generic mode: 1.38M PPS
>> >   driver mode: 4.15M PPS
>> > xdp_redirect_map_multi:
>> >   generic mode: 1.13M PPS
>> >   driver mode: 3.55M PPS
>
> With XDP_DROP in veth perr, the number looks much better
>
> xdp_redirect_map:
>   generic mode: 1.64M PPS
>   driver mode: 13.3M PPS
> xdp_redirect_map_multi:
>   generic mode: 1.29M PPS
>   driver mode: 8.5M PPS

Is this for a single interface in both cases? Look a bit odd that you
get such a big difference all of a sudden; is the redirect failing in
one of those cases (should be a hint in the ethtool stats, I think,
otherwise check xdp_monitor)?

>> > Kernel 5.7 + my patch(ingress i40e, egress i40e + veth)
>> > xdp_redirect_map_multi:
>> >   generic mode: 1.13M PPS
>> >   driver mode: 3.47M PPS
>
> But I don't know why this one get even a little slower..
>
> xdp_redirect_map_multi:
>   generic mode: 0.96M PPS
>   driver mode: 3.14M PPS

Yeah, this does seem a bit odd. Don't have any good ideas off the top of
my head, but maybe worth double-checking where the time is spent. You
can use 'perf' for this, but you need to make sure it's recording the
CPU that is processing packets...

-Toke