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From: Maryam Tahhan <mtahhan@redhat.com>
To: sdf@google.com, "Toke Høiland-Jørgensen" <toke@redhat.com>
Cc: Jakub Kicinski <kuba@kernel.org>,
	Martin KaFai Lau <martin.lau@linux.dev>,
	Jesper Dangaard Brouer <jbrouer@redhat.com>,
	brouer@redhat.com, bpf@vger.kernel.org, netdev@vger.kernel.org,
	xdp-hints@xdp-project.net, larysa.zaremba@intel.com,
	memxor@gmail.com, Lorenzo Bianconi <lorenzo@kernel.org>,
	Alexei Starovoitov <alexei.starovoitov@gmail.com>,
	Daniel Borkmann <borkmann@iogearbox.net>,
	Andrii Nakryiko <andrii.nakryiko@gmail.com>,
	dave@dtucker.co.uk, Magnus Karlsson <magnus.karlsson@intel.com>,
	bjorn@kernel.org
Subject: [xdp-hints] Re: [PATCH RFCv2 bpf-next 00/18] XDP-hints: XDP gaining access to HW offload hints via BTF
Date: Thu, 6 Oct 2022 09:19:36 +0100	[thread overview]
Message-ID: <be3f16a2-8422-4a34-3eb9-3943753d453e@redhat.com> (raw)
In-Reply-To: <Yz3RQbh2TocpnuX0@google.com>

On 05/10/2022 19:47, sdf@google.com wrote:
> On 10/05, Toke H�iland-J�rgensen wrote:
>> Stanislav Fomichev <sdf@google.com> writes:
> 
>> > On Tue, Oct 4, 2022 at 5:59 PM Jakub Kicinski <kuba@kernel.org> wrote:
>> >>
>> >> On Tue, 4 Oct 2022 17:25:51 -0700 Martin KaFai Lau wrote:
>> >> > A intentionally wild question, what does it take for the driver 
>> to return the
>> >> > hints.  Is the rx_desc and rx_queue enough?  When the xdp prog is 
>> calling a
>> >> > kfunc/bpf-helper, like 'hwtstamp = bpf_xdp_get_hwtstamp()', can 
>> the driver
>> >> > replace it with some inline bpf code (like how the inline code is 
>> generated for
>> >> > the map_lookup helper).  The xdp prog can then store the hwstamp 
>> in the meta
>> >> > area in any layout it wants.
>> >>
>> >> Since you mentioned it... FWIW that was always my preference rather 
>> than
>> >> the BTF magic :)  The jited image would have to be per-driver like we
>> >> do for BPF offload but that's easy to do from the technical
>> >> perspective (I doubt many deployments bind the same prog to multiple
>> >> HW devices)..
>> >
>> > +1, sounds like a good alternative (got your reply while typing)
>> > I'm not too versed in the rx_desc/rx_queue area, but seems like worst
>> > case that bpf_xdp_get_hwtstamp can probably receive a xdp_md ctx and
>> > parse it out from the pre-populated metadata?
>> >
>> > Btw, do we also need to think about the redirect case? What happens
>> > when I redirect one frame from a device A with one metadata format to
>> > a device B with another?
> 
>> Yes, we absolutely do! In fact, to me this (redirects) is the main
>> reason why we need the ID in the packet in the first place: when running
>> on (say) a veth, an XDP program needs to be able to deal with packets
>> from multiple physical NICs.
> 
>> As far as API is concerned, my hope was that we could solve this with a
>> CO-RE like approach where the program author just writes something like:
> 
>> hw_tstamp = bpf_get_xdp_hint("hw_tstamp", u64);
> 
>> and bpf_get_xdp_hint() is really a macro (or a special kind of
>> relocation?) and libbpf would do the following on load:
> 
>> - query the kernel BTF for all possible xdp_hint structs
>> - figure out which of them have an 'u64 hw_tstamp' member
>> - generate the necessary conditionals / jump table to disambiguate on
>>    the BTF_ID in the packet
> 
> 
>> Now, if this is better done by a kfunc I'm not terribly opposed to that
>> either, but I'm not sure it's actually better/easier to do in the kernel
>> than in libbpf at load time?
> 
> Replied in the other thread, but to reiterate here: then btf_id in the
> metadata has to stay and we either pre-generate those bpf_get_xdp_hint()
> at libbpf or at kfunc load time level as you mention.
> 
> But the program essentially has to handle all possible hints' btf ids 
> thrown
> at it by the system. Not sure about the performance in this case :-/
> Maybe that's something that can be hidden behind "I might receive forwarded
> packets and I know how to handle all metadata format" flag? By default,
> we'll pre-generate parsing only for that specific device?

I did a simple POC of Jespers xdp-hints with AF-XDP and CNDP (Cloud 
Native Data Plane). In the cases where my app had access to the HW I 
didn't need to handle all possible hints... I knew what Drivers were on 
the system and they were the hints I needed to deal with.

So at program init time I registered the relevant BTF_IDs (and some 
callback functions to handle them) from the NICs that were available to 
me in a simple tailq (tbh there were so few I could've probably used a 
static array).

When processing the hints then I only needed to invoke the appropriate 
callback function based on the received BTF_ID. I didn't have a massive 
chains of if...else if... else statements.

In the case where we have redirection to a virtual NIC and we don't 
necessarily know the underlying hints that are exposed to the app, could 
we not still use the xdp_hints (as proposed by Jesper) themselves to 
indicate the relevant drivers to the application? or even indicate them 
via a map or something?


  reply	other threads:[~2022-10-06  8:19 UTC|newest]

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-09-07 15:45 [xdp-hints] " Jesper Dangaard Brouer
2022-09-07 15:45 ` [xdp-hints] [PATCH RFCv2 bpf-next 01/18] libbpf: factor out BTF loading from load_module_btfs() Jesper Dangaard Brouer
2022-09-07 15:45 ` [xdp-hints] [PATCH RFCv2 bpf-next 02/18] libbpf: try to load vmlinux BTF from the kernel first Jesper Dangaard Brouer
2022-09-07 15:45 ` [xdp-hints] [PATCH RFCv2 bpf-next 03/18] libbpf: patch module BTF obj+type ID into BPF insns Jesper Dangaard Brouer
2022-09-07 15:45 ` [xdp-hints] [PATCH RFCv2 bpf-next 04/18] net: create xdp_hints_common and set functions Jesper Dangaard Brouer
2022-09-09 10:49   ` [xdp-hints] " Burakov, Anatoly
2022-09-09 14:13     ` Jesper Dangaard Brouer
2022-09-07 15:45 ` [xdp-hints] [PATCH RFCv2 bpf-next 05/18] net: add net_device feature flag for XDP-hints Jesper Dangaard Brouer
2022-09-07 15:45 ` [xdp-hints] [PATCH RFCv2 bpf-next 06/18] xdp: controlling XDP-hints from BPF-prog via helper Jesper Dangaard Brouer
2022-09-07 15:45 ` [xdp-hints] [PATCH RFCv2 bpf-next 07/18] i40e: Refactor i40e_ptp_rx_hwtstamp Jesper Dangaard Brouer
2022-09-07 15:45 ` [xdp-hints] [PATCH RFCv2 bpf-next 08/18] i40e: refactor i40e_rx_checksum with helper Jesper Dangaard Brouer
2022-09-07 15:45 ` [xdp-hints] [PATCH RFCv2 bpf-next 09/18] bpf: export btf functions for modules Jesper Dangaard Brouer
2022-09-07 15:45 ` [xdp-hints] [PATCH RFCv2 bpf-next 10/18] btf: Add helper for kernel modules to lookup full BTF ID Jesper Dangaard Brouer
2022-09-07 15:45 ` [xdp-hints] [PATCH RFCv2 bpf-next 11/18] i40e: add XDP-hints handling Jesper Dangaard Brouer
2022-09-07 15:46 ` [xdp-hints] [PATCH RFCv2 bpf-next 12/18] net: use XDP-hints in xdp_frame to SKB conversion Jesper Dangaard Brouer
2022-09-07 15:46 ` [xdp-hints] [PATCH RFCv2 bpf-next 13/18] mvneta: add XDP-hints support Jesper Dangaard Brouer
2022-09-07 15:46 ` [xdp-hints] [PATCH RFCv2 bpf-next 14/18] i40e: Add xdp_hints_union Jesper Dangaard Brouer
2022-09-07 15:46 ` [xdp-hints] [PATCH RFCv2 bpf-next 15/18] ixgbe: enable xdp-hints Jesper Dangaard Brouer
2022-09-07 15:46 ` [xdp-hints] [PATCH RFCv2 bpf-next 16/18] ixgbe: add rx timestamp xdp hints support Jesper Dangaard Brouer
2022-09-07 15:46 ` [xdp-hints] [PATCH RFCv2 bpf-next 17/18] xsk: AF_XDP xdp-hints support in desc options Jesper Dangaard Brouer
2022-09-08  8:06   ` [xdp-hints] " Magnus Karlsson
2022-09-08 10:10     ` Maryam Tahhan
2022-09-08 15:04       ` Jesper Dangaard Brouer
2022-09-09  6:43         ` Magnus Karlsson
2022-09-09  8:12           ` Maryam Tahhan
2022-09-09  9:42             ` Jesper Dangaard Brouer
2022-09-09 10:14               ` Magnus Karlsson
2022-09-09 12:35                 ` Jesper Dangaard Brouer
2022-09-09 12:44                   ` Magnus Karlsson
2022-09-07 15:46 ` [xdp-hints] [PATCH RFCv2 bpf-next 18/18] ixgbe: AF_XDP xdp-hints processing in ixgbe_clean_rx_irq_zc Jesper Dangaard Brouer
2022-09-08  9:30 ` [xdp-hints] Re: [PATCH RFCv2 bpf-next 00/18] XDP-hints: XDP gaining access to HW offload hints via BTF Alexander Lobakin
2022-09-09 13:48   ` Jesper Dangaard Brouer
2022-10-03 23:55 ` sdf
2022-10-04  9:29   ` Jesper Dangaard Brouer
2022-10-04 18:26     ` Stanislav Fomichev
2022-10-05  0:25       ` Martin KaFai Lau
2022-10-05  0:59         ` Jakub Kicinski
2022-10-05  1:02           ` Stanislav Fomichev
2022-10-05  1:24             ` Jakub Kicinski
2022-10-05  2:15               ` Stanislav Fomichev
2022-10-05 19:26                 ` Martin KaFai Lau
2022-10-06  9:14                   ` Magnus Karlsson
2022-10-06 15:29                     ` Jesper Dangaard Brouer
2022-10-11  6:29                       ` Martin KaFai Lau
2022-10-11 11:57                         ` Jesper Dangaard Brouer
2022-10-05 10:06             ` Toke Høiland-Jørgensen
2022-10-05 18:47               ` sdf
2022-10-06  8:19                 ` Maryam Tahhan [this message]
2022-10-06 17:22                   ` sdf
2022-10-05 14:19             ` Jesper Dangaard Brouer
2022-10-06 14:59               ` Jakub Kicinski
2022-10-05 13:43         ` Jesper Dangaard Brouer
2022-10-05 16:29       ` Jesper Dangaard Brouer
2022-10-05 18:43         ` sdf
2022-10-06 17:47           ` Jesper Dangaard Brouer
2022-10-07 15:05             ` David Ahern
2022-10-05 13:14     ` Burakov, Anatoly

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