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From: Jakub Kicinski <kuba@kernel.org>
To: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: Netdev <netdev@vger.kernel.org>,
	"Thomas Ptacek" <thomas@sockpuppet.org>,
	"Adhipati Blambangan" <adhipati@tuta.io>,
	"David Ahern" <dsahern@gmail.com>,
	"Toke Høiland-Jørgensen" <toke@redhat.com>,
	"Alexei Starovoitov" <alexei.starovoitov@gmail.com>
Subject: Re: [PATCH net v4] net: xdp: account for layer 3 packets in generic skb handler
Date: Fri, 14 Aug 2020 08:31:53 -0700	[thread overview]
Message-ID: <20200814083153.06b180b5@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> (raw)
In-Reply-To: <CAHmME9rbRrdV0ePxT0DgurGdEKOWiEi5mH5Wtg=aJwSA6fxwMg@mail.gmail.com>

On Fri, 14 Aug 2020 08:56:48 +0200 Jason A. Donenfeld wrote:
> On Thu, Aug 13, 2020 at 11:01 PM Jakub Kicinski <kuba@kernel.org> wrote:
> > > I had originally dropped this patch, but the issue kept coming up in
> > > user reports, so here's a v4 of it. Testing of it is still rather slim,
> > > but hopefully that will change in the coming days.  
> >
> > Here an alternative patch, untested:  
> 
> Funny. But come on now... Why would we want to deprive our users of
> system consistency?

We should try for consistency between xdp and cls_bpf instead.

> Doesn't it make sense to allow users to use the same code across
> interfaces? You actually want them to rewrite their code to use a
> totally different trigger point just because of some weird kernel
> internals between interfaces?

We're not building an abstraction over the kernel stack so that users
won't have to worry how things work. Users need to have a minimal
understanding of how specific hooks integrate with the stack and what
they are for. And therefore why cls_bpf is actually more efficient to
use in L3 tunnel case.

> Why not make XDP more useful and more generic across interfaces? It's
> very common for systems to be receiving packets with a heavy ethernet
> card from the current data center, in addition to receiving packets
> from a tunnel interface connected to a remote data center, with a need
> to run the same XDP program on both interfaces. Why not support that
> kind of simplicity?
> 
> This is _actually_ something that's come up _repeatedly_. This is a
> real world need from real users who are doing real things. Why not
> help them?

I'm sure it comes up repeatedly because we don't return any errors,
so people waste time investigating why it doesn't work.

> It's not at the expense of any formal consistency, or performance, or
> even semantic perfection. It costs very little to support these
> popular use cases.

  parent reply	other threads:[~2020-08-14 15:32 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-13 19:58 Jason A. Donenfeld
2020-08-13 21:01 ` Jakub Kicinski
2020-08-14  6:56   ` Jason A. Donenfeld
2020-08-14  7:30     ` [PATCH net v5] " Jason A. Donenfeld
2020-08-14 20:55       ` David Miller
2020-08-14 20:57         ` Jason A. Donenfeld
2020-08-15  7:41         ` [PATCH net v6] " Jason A. Donenfeld
2020-08-19  7:07           ` Jesper Dangaard Brouer
2020-08-19 23:22           ` David Miller
2020-08-20  9:13             ` Jason A. Donenfeld
2020-08-20 18:55               ` David Miller
2020-08-20 20:29                 ` Jason A. Donenfeld
2020-08-14 15:31     ` Jakub Kicinski [this message]
2020-08-14 21:04       ` [PATCH net v4] " Jason A. Donenfeld
2020-08-14 21:26         ` David Miller
2020-08-15  7:54           ` Jason A. Donenfeld
2020-08-14 21:14       ` David Miller

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