netdev - Re: [Intel-wired-lan] FW: [PATCH bpf-next 2/4] xsk: allow AF_XDP sockets to receive packets directly from a queue

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Message-ID: <CAADnVQLJ95j5jfh5jFApjs4bYzOxuPcrMgH9jbdGGvOWQEPRyQ@mail.gmail.com>
Date:   Thu, 31 Oct 2019 16:15:34 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     "Samudrala, Sridhar" <sridhar.samudrala@...el.com>
Cc:     Björn Töpel <bjorn.topel@...il.com>,
        Björn Töpel <bjorn.topel@...el.com>,
        bpf <bpf@...r.kernel.org>,
        intel-wired-lan <intel-wired-lan@...ts.osuosl.org>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        "Fijalkowski, Maciej" <maciej.fijalkowski@...el.com>,
        "Karlsson, Magnus" <magnus.karlsson@...el.com>,
        Network Development <netdev@...r.kernel.org>,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        "Herbert, Tom" <tom.herbert@...el.com>
Subject: Re: [Intel-wired-lan] FW: [PATCH bpf-next 2/4] xsk: allow AF_XDP
 sockets to receive packets directly from a queue

On Thu, Oct 31, 2019 at 3:38 PM Samudrala, Sridhar
<sridhar.samudrala@...el.com> wrote:
>
> Alexei, Jakub
>
> Do you think it will be possible to avoid this overhead when mitigations are turned ON?

yes

> The other part of the overhead is going through the redirect path.
>
> Can i assume that your silence as an indication that you are now okay with optional bypass
> flag as long as it doesn't effect the normal XDP datapath. If so, i will respin and submit
> the patches against the latest bpf-next

I'm still against it.
Looks like the only motivation for it is extra overhead due to retpolines.
imo it's not a good reason to introduce a bunch of extra code helping
single kernel feature.
We will have proper solution for indirect calls.