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From: Alexander Lobakin <aleksander.lobakin@intel.com>
To: Larysa Zaremba <larysa.zaremba@intel.com>,
	Jesper Dangaard Brouer <jbrouer@redhat.com>,
	John Fastabend <john.fastabend@gmail.com>
Cc: brouer@redhat.com, bpf@vger.kernel.org, ast@kernel.org,
	daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev,
	song@kernel.org, yhs@fb.com, kpsingh@kernel.org, sdf@google.com,
	haoluo@google.com, jolsa@kernel.org,
	David Ahern <dsahern@gmail.com>, Jakub Kicinski <kuba@kernel.org>,
	Willem de Bruijn <willemb@google.com>,
	Anatoly Burakov <anatoly.burakov@intel.com>,
	Alexander Lobakin <alexandr.lobakin@intel.com>,
	Magnus Karlsson <magnus.karlsson@gmail.com>,
	Maryam Tahhan <mtahhan@redhat.com>,
	xdp-hints@xdp-project.net, netdev@vger.kernel.org,
	"David S. Miller" <davem@davemloft.net>,
	Alexander Duyck <alexander.duyck@gmail.com>
Subject: [xdp-hints] Re: [PATCH bpf-next v2 12/20] xdp: Add checksum level hint
Date: Mon, 10 Jul 2023 18:58:30 +0200	[thread overview]
Message-ID: <51bf0e2a-017b-f89b-e202-bc3978d60623@intel.com> (raw)
In-Reply-To: <ZKa4aCHDrG2ZVI8H@lincoln>

From: Larysa Zaremba <larysa.zaremba@intel.com>
Date: Thu, 6 Jul 2023 14:49:44 +0200

> On Thu, Jul 06, 2023 at 02:38:33PM +0200, Larysa Zaremba wrote:
>> On Thu, Jul 06, 2023 at 11:04:49AM +0200, Jesper Dangaard Brouer wrote:
>>>
>>>
>>> On 06/07/2023 07.50, John Fastabend wrote:
>>>> Larysa Zaremba wrote:
>>>>> On Tue, Jul 04, 2023 at 12:39:06PM +0200, Jesper Dangaard Brouer wrote:
>>>>>> Cc. DaveM+Alex Duyck, as I value your insights on checksums.

[...]

>>>>>>>>> + * Return:
>>>>>>>>> + * * Returns 0 on success or ``-errno`` on error.
>>>>>>>>> + * * ``-EOPNOTSUPP`` : device driver doesn't implement kfunc
>>>>>>>>> + * * ``-ENODATA``    : Checksum was not validated
>>>>>>>>> + */
>>>>>>>>> +__bpf_kfunc int bpf_xdp_metadata_rx_csum_lvl(const struct xdp_md *ctx, u8 *csum_level)
>>>>>>>>
>>>>>>>> Istead of ENODATA should we return what would be put in the ip_summed field
>>>>>>>> CHECKSUM_{NONE, UNNECESSARY, COMPLETE, PARTIAL}? Then sig would be,
>>>>>>
>>>>>> I was thinking the same, what about checksum "type".
>>>>>>
>>>>>>>>
>>>>>>>>    bpf_xdp_metadata_rx_csum_lvl(const struct xdp_md *ctx, u8 *type, u8 *lvl);
>>>>>>>>
>>>>>>>> or something like that? Or is the thought that its not really necessary?
>>>>>>>> I don't have a strong preference but figured it was worth asking.
>>>>>>>>
>>>>>>>
>>>>>>> I see no value in returning CHECKSUM_COMPLETE without the actual checksum value.
>>>>>>> Same with CHECKSUM_PARTIAL and csum_start. Returning those values too would
>>>>>>> overcomplicate the function signature.
>>>>>>
>>>>>> So, this kfunc bpf_xdp_metadata_rx_csum_lvl() success is it equivilent to
>>>>>> CHECKSUM_UNNECESSARY?
>>>>>
>>>>> This is 100% true for physical NICs, it's more complicated for veth, bacause it
>>>>> often receives CHECKSUM_PARTIAL, which shouldn't normally apprear on RX, but is
>>>>> treated by the network stack as a validated checksum, because there is no way
>>>>> internally generated packet could be messed up. I would be grateful if you could
>>>>> look at the veth patch and share your opinion about this.
>>>>>
>>>>>>
>>>>>> Looking at documentation[1] (generated from skbuff.h):
>>>>>>   [1] https://kernel.org/doc/html/latest/networking/skbuff.html#checksumming-of-received-packets-by-device
>>>>>>
>>>>>> Is the idea that we can add another kfunc (new signature) than can deal
>>>>>> with the other types of checksums (in a later kernel release)?
>>>>>>
>>>>>
>>>>> Yes, that is the idea.
>>>>
>>>> If we think there is a chance we might need another kfunc we should add it
>>>> in the same kfunc. It would be unfortunate to have to do two kfuncs when
>>>> one would work. It shouldn't cost much/anything(?) to hardcode the type for
>>>> most cases? I think if we need it later I would advocate for updating this
>>>> kfunc to support it. Of course then userspace will have to swivel on the
>>>> kfunc signature.
>>>>
>>>
>>> I think it might make sense to have 3 kfuncs for checksumming.

Isn't that overcomplicating? 3 callbacks for just one damn thing. IOW I
agree with John.

PARTIAL and COMPLETE are mutually exclusive. Their "additional" output
can be unionized. Level is 2 bits, status is 2 bits. Level makes sense
only with UNNECESSARY (correct me if I'm wrong).
IOW the kfunc could return:

-errno - not implemented or something went wrong
0 - none
1 - complete
2 - partial
3 + lvl - unnecessary

(CHECKSUM_* defs could be shuffled accordingly)

Then `if (ret > 2)` would mean UNNECESSARY and most programs could stop
here already. Programs wanting to extract the level can do `ret - 3`.
One additional pointer to u32 (union) to fetch additional data. I would
even say "BPF prog can pass NULL if it doesn't care", but OTOH I dunno
how to validate PARTIAL then :D (COMPLETE usually assumes it's valid)

>>> As this would allow BPF-prog to focus on CHECKSUM_UNNECESSARY, and then
>>> only call additional kfunc for extracting e.g csum_start  + csum_offset
>>> when type is CHECKSUM_PARTIAL.
>>>
>>> We could extend bpf_xdp_metadata_rx_csum_lvl() to give the csum_type
>>> CHECKSUM_{NONE, UNNECESSARY, COMPLETE, PARTIAL}.
>>>
>>>  int bpf_xdp_metadata_rx_csum_lvl(*ctx, u8 *csum_level, u8 *csum_type)
>>>
>>> And then add two kfunc e.g.
>>>  (1) bpf_xdp_metadata_rx_csum_partial(ctx, start, offset)
>>>  (2) bpf_xdp_metadata_rx_csum_complete(ctx, csum)
>>>
>>> Pseudo BPF-prog code:
>>>
>>>  err = bpf_xdp_metadata_rx_csum_lvl(ctx, level, type);
>>>  if (!err && type != CHECKSUM_UNNECESSARY) {

And hurt cool HW which by default returns COMPLETE? }:>

>>>      if (type == CHECKSUM_PARTIAL)
>>>          err = bpf_xdp_metadata_rx_csum_partial(ctx, start, offset);
>>>      if (type == CHECKSUM_COMPLETE)
>>>          err = bpf_xdp_metadata_rx_csum_complete(ctx, csum);

I don't feel like 1 hotpath `if` is worth multiplying kfuncs.

[...]

Thanks,
Olek

  reply	other threads:[~2023-07-10 16:59 UTC|newest]

Thread overview: 66+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-07-03 18:12 [xdp-hints] [PATCH bpf-next v2 00/20] XDP metadata via kfuncs for ice Larysa Zaremba
2023-07-03 18:12 ` [xdp-hints] [PATCH bpf-next v2 01/20] ice: make RX hash reading code more reusable Larysa Zaremba
2023-07-03 18:12 ` [xdp-hints] [PATCH bpf-next v2 02/20] ice: make RX HW timestamp " Larysa Zaremba
2023-07-04 10:04   ` [xdp-hints] " Larysa Zaremba
2023-07-03 18:12 ` [xdp-hints] [PATCH bpf-next v2 03/20] ice: make RX checksum checking " Larysa Zaremba
2023-07-03 18:12 ` [xdp-hints] [PATCH bpf-next v2 04/20] ice: Make ptype internal to descriptor info processing Larysa Zaremba
2023-07-03 18:12 ` [xdp-hints] [PATCH bpf-next v2 05/20] ice: Introduce ice_xdp_buff Larysa Zaremba
2023-07-03 18:12 ` [xdp-hints] [PATCH bpf-next v2 06/20] ice: Support HW timestamp hint Larysa Zaremba
2023-07-05 17:30   ` [xdp-hints] " Stanislav Fomichev
2023-07-06 14:22     ` Larysa Zaremba
2023-07-06 16:39       ` Stanislav Fomichev
2023-07-10 15:49         ` Larysa Zaremba
2023-07-10 18:12           ` Stanislav Fomichev
2023-07-03 18:12 ` [xdp-hints] [PATCH bpf-next v2 07/20] ice: Support RX hash XDP hint Larysa Zaremba
2023-07-03 18:12 ` [xdp-hints] [PATCH bpf-next v2 08/20] ice: Support XDP hints in AF_XDP ZC mode Larysa Zaremba
2023-07-03 18:12 ` [xdp-hints] [PATCH bpf-next v2 09/20] xdp: Add VLAN tag hint Larysa Zaremba
2023-07-03 20:15   ` [xdp-hints] " John Fastabend
2023-07-04  8:23     ` Larysa Zaremba
2023-07-04 10:23       ` Jesper Dangaard Brouer
2023-07-04 11:02         ` Larysa Zaremba
2023-07-04 14:18           ` Jesper Dangaard Brouer
2023-07-06 14:46             ` Larysa Zaremba
2023-07-07 13:57               ` Jesper Dangaard Brouer
2023-07-07 17:58                 ` Larysa Zaremba
2023-07-03 18:12 ` [xdp-hints] [PATCH bpf-next v2 10/20] ice: Implement " Larysa Zaremba
2023-07-03 18:12 ` [xdp-hints] [PATCH bpf-next v2 11/20] ice: use VLAN proto from ring packet context in skb path Larysa Zaremba
2023-07-03 18:12 ` [xdp-hints] [PATCH bpf-next v2 12/20] xdp: Add checksum level hint Larysa Zaremba
2023-07-03 20:38   ` [xdp-hints] " John Fastabend
2023-07-04  9:24     ` Larysa Zaremba
2023-07-04 10:39       ` Jesper Dangaard Brouer
2023-07-04 11:19         ` Larysa Zaremba
2023-07-06  5:50           ` John Fastabend
2023-07-06  9:04             ` Jesper Dangaard Brouer
2023-07-06 12:38               ` Larysa Zaremba
2023-07-06 12:49                 ` Larysa Zaremba
2023-07-10 16:58                   ` Alexander Lobakin [this message]
2023-07-03 18:12 ` [xdp-hints] [PATCH bpf-next v2 13/20] ice: Implement " Larysa Zaremba
2023-07-03 18:12 ` [xdp-hints] [PATCH bpf-next v2 14/20] selftests/bpf: Allow VLAN packets in xdp_hw_metadata Larysa Zaremba
2023-07-05 17:31   ` [xdp-hints] " Stanislav Fomichev
2023-07-03 18:12 ` [xdp-hints] [PATCH bpf-next v2 15/20] net, xdp: allow metadata > 32 Larysa Zaremba
2023-07-03 21:06   ` [xdp-hints] " John Fastabend
2023-07-06 14:51     ` Larysa Zaremba
2023-07-10 14:01       ` Alexander Lobakin
2023-07-03 18:12 ` [xdp-hints] [PATCH bpf-next v2 16/20] selftests/bpf: Add flags and new hints to xdp_hw_metadata Larysa Zaremba
2023-07-04 11:03   ` [xdp-hints] " Jesper Dangaard Brouer
2023-07-04 11:04     ` Larysa Zaremba
2023-07-03 18:12 ` [xdp-hints] [PATCH bpf-next v2 17/20] veth: Implement VLAN tag and checksum level XDP hint Larysa Zaremba
2023-07-05 17:25   ` [xdp-hints] " Stanislav Fomichev
2023-07-06  9:57     ` Jesper Dangaard Brouer
2023-07-06 10:15       ` Larysa Zaremba
2023-07-03 18:12 ` [xdp-hints] [PATCH bpf-next v2 18/20] selftests/bpf: Use AF_INET for TX in xdp_metadata Larysa Zaremba
2023-07-05 17:39   ` [xdp-hints] " Stanislav Fomichev
2023-07-06 14:11     ` Larysa Zaremba
2023-07-06 17:25       ` Stanislav Fomichev
2023-07-06 17:27       ` Stanislav Fomichev
2023-07-07  8:33         ` Larysa Zaremba
2023-07-07 16:49           ` Stanislav Fomichev
2023-07-07 16:58             ` Larysa Zaremba
2023-07-03 18:12 ` [xdp-hints] [PATCH bpf-next v2 19/20] selftests/bpf: Check VLAN tag and proto " Larysa Zaremba
2023-07-05 17:41   ` [xdp-hints] " Stanislav Fomichev
2023-07-06 10:10   ` Jesper Dangaard Brouer
2023-07-06 10:13     ` Larysa Zaremba
2023-07-03 18:12 ` [xdp-hints] [PATCH bpf-next v2 20/20] selftests/bpf: check checksum level " Larysa Zaremba
2023-07-05 17:41   ` [xdp-hints] " Stanislav Fomichev
2023-07-06 10:25   ` Jesper Dangaard Brouer
2023-07-06 12:02     ` Larysa Zaremba

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