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From: "Björn Töpel" <bjorn.topel@intel.com>
To: "Toke Høiland-Jørgensen" <toke@redhat.com>,
	"Björn Töpel" <bjorn.topel@gmail.com>,
	ast@kernel.org, daniel@iogearbox.net, netdev@vger.kernel.org,
	bpf@vger.kernel.org
Cc: magnus.karlsson@intel.com, maciej.fijalkowski@intel.com,
	kuba@kernel.org, jonathan.lemon@gmail.com, maximmi@nvidia.com,
	davem@davemloft.net, hawk@kernel.org, john.fastabend@gmail.com,
	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: Wed, 20 Jan 2021 16:18:50 +0100	[thread overview]
Message-ID: <3c6feb0d-6a64-2251-3cac-c79cff29d85c@intel.com> (raw)
In-Reply-To: <87k0s74q1a.fsf@toke.dk>

On 2021-01-20 15:54, Toke Høiland-Jørgensen wrote:
> Björn Töpel <bjorn.topel@intel.com> writes:
> 
>> On 2021-01-20 13:50, Toke Høiland-Jørgensen wrote:
>>> Björn Töpel <bjorn.topel@gmail.com> writes:
>>>
>>>> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
>>>> index c001766adcbc..bbc7d9a57262 100644
>>>> --- a/include/uapi/linux/bpf.h
>>>> +++ b/include/uapi/linux/bpf.h
>>>> @@ -3836,6 +3836,12 @@ union bpf_attr {
>>>>     *	Return
>>>>     *		A pointer to a struct socket on success or NULL if the file is
>>>>     *		not a socket.
>>>> + *
>>>> + * long bpf_redirect_xsk(struct xdp_buff *xdp_md, u64 action)
>>>> + *	Description
>>>> + *		Redirect to the registered AF_XDP socket.
>>>> + *	Return
>>>> + *		**XDP_REDIRECT** on success, otherwise the action parameter is returned.
>>>>     */
>>>
>>> I think it would be better to make the second argument a 'flags'
>>> argument and make values > XDP_TX invalid (like we do in
>>> bpf_xdp_redirect_map() now). By allowing any value as return you lose
>>> the ability to turn it into a flags argument later...
>>>
>>
>> Yes, but that adds a run-time check. I prefer this non-checked version,
>> even though it is a bit less futureproof.
> 
> That...seems a bit short-sighted? :)
> Can you actually see a difference in your performance numbers?
>

I would rather add an additional helper *if* we see the need for flags,
instead of paying for that upfront. For me, BPF is about being able to
specialize, and not having one call with tons of checks.

(Related; Going forward, the growing switch() for redirect targets in
xdp_do_redirect() is a concern for me...)

And yes, even with all those fancy branch predictors, less instructions
is still less. :-) (It shows in my ubenchs.)


Björn


  reply	other threads:[~2021-01-20 15:20 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 [this message]
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
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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