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From: "Björn Töpel" <bjorn.topel@intel.com>
To: "Alexei Starovoitov" <alexei.starovoitov@gmail.com>,
	"Toke Høiland-Jørgensen" <toke@redhat.com>
Cc: "Björn Töpel" <bjorn.topel@gmail.com>,
	"Alexei Starovoitov" <ast@kernel.org>,
	"Daniel Borkmann" <daniel@iogearbox.net>,
	"Network Development" <netdev@vger.kernel.org>,
	bpf <bpf@vger.kernel.org>,
	"Karlsson, Magnus" <magnus.karlsson@intel.com>,
	"Fijalkowski, Maciej" <maciej.fijalkowski@intel.com>,
	"Jakub Kicinski" <kuba@kernel.org>,
	"Jonathan Lemon" <jonathan.lemon@gmail.com>,
	maximmi@nvidia.com, "David S. Miller" <davem@davemloft.net>,
	"Jesper Dangaard Brouer" <hawk@kernel.org>,
	"John Fastabend" <john.fastabend@gmail.com>,
	"Ciara Loftus" <ciara.loftus@intel.com>,
	weqaar.a.janjua@intel.com
Subject: Re: [PATCH bpf-next v2 4/8] xsk: register XDP sockets at bind(), and add new AF_XDP BPF helper
Date: Thu, 21 Jan 2021 09:18:48 +0100	[thread overview]
Message-ID: <36d92c18-e0a0-a4dc-3797-539f8fe6333c@intel.com> (raw)
In-Reply-To: <CAADnVQ+R5JHhqUFnB_o3nJkkkcEtvO_Vk+xSDFiqP9dZ9H6vxw@mail.gmail.com>

On 2021-01-20 22:15, Alexei Starovoitov wrote:
> On Wed, Jan 20, 2021 at 12:26 PM Toke Høiland-Jørgensen <toke@redhat.com> wrote:
>>
>> This argument, however, I buy: bpf_redirect() is the single-purpose
>> helper for redirecting to an ifindex, bpf_redirect_xsk() is the
>> single-purpose helper for redirecting to an XSK, and bpf_redirect_map()
>> is the generic one that does both of those and more. Fair enough,
>> consider me convinced :)
>>
>>> A lot of back-and-forth for *one* if-statement, but it's kind of a
>>> design thing for me. ;-)
>>
>> Surely you don't mean to imply that you have *better* things to do with
>> your time than have a 10-emails-long argument over a single if
>> statement? ;)
> 
> After reading this thread I think I have to pour cold water on the design.
> 
> The performance blip comes from hard coded assumptions:
> + queue_id = xdp->rxq->queue_index;
> + xs = READ_ONCE(dev->_rx[queue_id].xsk);
>

Yes, one can see this as a constrained map:

* The map belongs to a certain netdev.
* Each entry corresponds to a certain queue id.

I.e if we do a successful (non-NULL) lookup, we *know* that all sockets
in that map belong to the netdev, and has the correct queue id.

By doing that we can get rid of two run-time checks: "Is the socket
bound to this netdev?" and "Is this the correct queue id?".

> bpf can have specialized helpers, but imo this is beyond what's reasonable.
> Please move such things into the program and try to make
> bpf_redirect_map faster.
>

I obviously prefer this path, and ideally combined with a way to even
more specialize xdp_do_redirect(). Then again, you are the maintainer! :-)

Maybe an alternative be adding a new type of XSKMAP constrained in the
similar way as above, and continue with bpf_redirect_map(), but with
this new map the index argument would be ignored. Unfortunately the BPF
context (xdp_buff in this case) is not passed to bpf_redirect_map(), so
getting the actual queue_id in the helper is hard. Adding the context as
an additional argument would be a new helper...

I'll need to think a bit more about it. Input/ideas are welcome!


> Making af_xdp non-root is orthogonal. If there is actual need for that
> it has to be designed thoroughly and not presented as "this helper may
> help to do that".
> I don't think "may" will materialize unless people actually work
> toward the goal of non-root.
> 

Fair enough! Same goal could be reached using the existing map approach.


Björn

  reply	other threads:[~2021-01-21  8:24 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-19 15:50 [PATCH bpf-next v2 0/8] Introduce bpf_redirect_xsk() helper Björn Töpel
2021-01-19 15:50 ` [PATCH bpf-next v2 1/8] xdp: restructure redirect actions Björn Töpel
2021-01-20 12:44   ` Toke Høiland-Jørgensen
2021-01-20 13:40     ` Björn Töpel
2021-01-20 14:52       ` Toke Høiland-Jørgensen
2021-01-20 15:49         ` Björn Töpel
2021-01-20 16:30           ` Toke Høiland-Jørgensen
2021-01-20 17:26             ` Björn Töpel
2021-01-19 15:50 ` [PATCH bpf-next v2 2/8] xsk: remove explicit_free parameter from __xsk_rcv() Björn Töpel
2021-01-19 15:50 ` [PATCH bpf-next v2 3/8] xsk: fold xp_assign_dev and __xp_assign_dev Björn Töpel
2021-01-19 15:50 ` [PATCH bpf-next v2 4/8] xsk: register XDP sockets at bind(), and add new AF_XDP BPF helper Björn Töpel
2021-01-20  8:25   ` kernel test robot
2021-01-20  8:41     ` Björn Töpel
2021-01-20  8:50   ` kernel test robot
2021-01-20 12:50   ` Toke Høiland-Jørgensen
2021-01-20 13:25     ` Björn Töpel
2021-01-20 14:54       ` Toke Høiland-Jørgensen
2021-01-20 15:18         ` Björn Töpel
2021-01-20 17:29           ` Toke Høiland-Jørgensen
2021-01-20 18:22             ` Björn Töpel
2021-01-20 20:26               ` Toke Høiland-Jørgensen
2021-01-20 21:15                 ` Alexei Starovoitov
2021-01-21  8:18                   ` Björn Töpel [this message]
2021-01-19 15:50 ` [PATCH bpf-next v2 5/8] libbpf, xsk: select AF_XDP BPF program based on kernel version Björn Töpel
2021-01-20 12:52   ` Toke Høiland-Jørgensen
2021-01-20 13:25     ` Björn Töpel
2021-01-20 14:49       ` Björn Töpel
2021-01-20 15:11         ` Toke Høiland-Jørgensen
2021-01-20 15:27           ` Björn Töpel
2021-01-20 17:30             ` Toke Høiland-Jørgensen
2021-01-20 18:25             ` Alexei Starovoitov
2021-01-20 18:30               ` Björn Töpel
2021-01-20 14:56       ` Toke Høiland-Jørgensen
2021-01-19 15:50 ` [PATCH bpf-next v2 6/8] libbpf, xsk: select bpf_redirect_xsk(), if supported Björn Töpel
2021-01-19 15:50 ` [PATCH bpf-next v2 7/8] selftest/bpf: add XDP socket tests for bpf_redirect_{xsk, map}() Björn Töpel
2021-01-21  7:39   ` Andrii Nakryiko
2021-01-21 12:31     ` Björn Töpel
2021-01-19 15:50 ` [PATCH bpf-next v2 8/8] selftest/bpf: remove a lot of ifobject casting in xdpxceiver Björn Töpel
2021-01-20 13:15 ` [PATCH bpf-next v2 0/8] Introduce bpf_redirect_xsk() helper Maxim Mikityanskiy
2021-01-20 13:27   ` Björn Töpel
2021-01-20 15:57   ` Jesper Dangaard Brouer
2021-01-20 16:19     ` Maciej Fijalkowski
2021-01-21 17:01       ` Jesper Dangaard Brouer
2021-01-22  8:59         ` Magnus Karlsson
2021-01-22  9:45           ` Maciej Fijalkowski

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