netdev - Re: [PATCH bpf-next v4 0/2] Optimize bpf_redirect_map()/xdp_do

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Message-ID: <87pn0nyrzo.fsf@toke.dk>
Date:   Fri, 26 Feb 2021 12:43:07 +0100
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Björn Töpel <bjorn.topel@...el.com>,
        Björn Töpel <bjorn.topel@...il.com>,
        ast@...nel.org, daniel@...earbox.net, netdev@...r.kernel.org,
        bpf@...r.kernel.org
Cc:     maciej.fijalkowski@...el.com, hawk@...nel.org,
        magnus.karlsson@...el.com, john.fastabend@...il.com,
        kuba@...nel.org, davem@...emloft.net
Subject: Re: [PATCH bpf-next v4 0/2] Optimize
 bpf_redirect_map()/xdp_do_redirect()

Björn Töpel <bjorn.topel@...el.com> writes:

> On 2021-02-26 12:35, Toke Høiland-Jørgensen wrote:
>> Björn Töpel <bjorn.topel@...il.com> writes:
>> 
>>> Hi XDP-folks,
>>>
>>> This two patch series contain two optimizations for the
>>> bpf_redirect_map() helper and the xdp_do_redirect() function.
>>>
>>> The bpf_redirect_map() optimization is about avoiding the map lookup
>>> dispatching. Instead of having a switch-statement and selecting the
>>> correct lookup function, we let bpf_redirect_map() be a map operation,
>>> where each map has its own bpf_redirect_map() implementation. This way
>>> the run-time lookup is avoided.
>>>
>>> The xdp_do_redirect() patch restructures the code, so that the map
>>> pointer indirection can be avoided.
>>>
>>> Performance-wise I got 3% improvement for XSKMAP
>>> (sample:xdpsock/rx-drop), and 4% (sample:xdp_redirect_map) on my
>>> machine.
>>>
>>> More details in each commit.
>>>
>>> @Jesper/Toke I dropped your Acked-by: on the first patch, since there
>>> were major restucturing. Please have another look! Thanks!
>> 
>> Will do! Did you update the performance numbers above after that change?
>>
>
> I did. The XSKMAP performance stayed the same (no surprise, since the
> code was the same). However, for the DEVMAP the v4 got rid of a call, so
> it *should* be a bit better, but for some reason it didn't show on my
> machine.

Alright, fair enough - pesky real world not lining up with expectations!
Maybe Jesper has additional suggestions, but I can live with the 4%
improvement ;)

-Toke