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From: "Toke Høiland-Jørgensen" <toke@redhat.com>
To: Jakub Kicinski <kuba@kernel.org>
Cc: John Fastabend <john.fastabend@gmail.com>,
	Alexei Starovoitov <alexei.starovoitov@gmail.com>,
	Lorenzo Bianconi <lorenzo@kernel.org>, bpf <bpf@vger.kernel.org>,
	Network Development <netdev@vger.kernel.org>,
	Lorenzo Bianconi <lorenzo.bianconi@redhat.com>,
	"David S. Miller" <davem@davemloft.net>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	shayagr@amazon.com, David Ahern <dsahern@kernel.org>,
	Jesper Dangaard Brouer <brouer@redhat.com>,
	Eelco Chaudron <echaudro@redhat.com>,
	Jason Wang <jasowang@redhat.com>,
	Alexander Duyck <alexander.duyck@gmail.com>,
	Saeed Mahameed <saeed@kernel.org>,
	"Fijalkowski, Maciej" <maciej.fijalkowski@intel.com>,
	"Karlsson, Magnus" <magnus.karlsson@intel.com>,
	tirthendu.sarkar@intel.com
Subject: Re: [PATCH v14 bpf-next 00/18] mvneta: introduce XDP multi-buffer support
Date: Tue, 21 Sep 2021 00:44:42 +0200	[thread overview]
Message-ID: <87ilyu50kl.fsf@toke.dk> (raw)
In-Reply-To: <20210920142542.7b451b78@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>

Jakub Kicinski <kuba@kernel.org> writes:

> On Mon, 20 Sep 2021 23:01:48 +0200 Toke Høiland-Jørgensen wrote:
>> > In fact I don't think there is anything infra can do better for
>> > flushing than the prog itself:
>> >
>> > 	bool mod = false;
>> >
>> > 	ptr = bpf_header_pointer(...);
>> > 	...
>> > 	if (some_cond(...)) {
>> > 		change_packet(...);
>> > 		mod = true;
>> > 	}
>> > 	...
>> > 	if (mod)  
>> 
>> to have an additional check like:
>> 
>> if (mod && ptr == stack)
>> 
>> (or something to that effect). No?
>
> Good point. Do you think we should have the kernel add/inline this
> optimization or have the user do it explicitly.

Hmm, good question. On the one hand it seems like an easy optimisation
to add, but on the other hand maybe the caller has other logic that can
better know how/when to omit the check.

Hmm, but the helper needs to check it anyway, doesn't it? At least it
can't just blindly memcpy() if the source and destination would be the
same...

> The draft API was:
>
> void *xdp_mb_pointer_flush(struct xdp_buff *xdp_md, u32 flags, 
>                            u32 offset, u32 len, void *stack_buf)
>
> Which does not take the ptr returned by header_pointer(), but that's
> easy to add (well, easy other than the fact it'd be the 6th arg).

I guess we could play some trickery with stuffing offset/len/flags into
one or two u64s to save an argument or two?

> BTW I drafted the API this way to cater to the case where flush()
> is called without a prior call to header_pointer(). For when packet
> trailer or header is populated directly from a map value. Dunno if
> that's actually useful, either.

Ah, didn't think of that; so then it really becomes a generic
xdp_store_bytes()-type helper? Might be useful, I suppose. Adding
headers is certainly a fairly common occurrence, but dunno to what
extent they'd be copied wholesale from a map (hadn't thought about doing
that before either).

-Toke


  reply	other threads:[~2021-09-20 22:48 UTC|newest]

Thread overview: 58+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-10 16:14 [PATCH v14 bpf-next 00/18] mvneta: introduce XDP multi-buffer support Lorenzo Bianconi
2021-09-10 16:14 ` [PATCH v14 bpf-next 01/18] net: skbuff: add size metadata to skb_shared_info for xdp Lorenzo Bianconi
2021-09-10 16:18   ` Jesper Dangaard Brouer
2021-09-10 16:14 ` [PATCH v14 bpf-next 02/18] xdp: introduce flags field in xdp_buff/xdp_frame Lorenzo Bianconi
2021-09-10 16:19   ` Jesper Dangaard Brouer
2021-09-10 16:14 ` [PATCH v14 bpf-next 03/18] net: mvneta: update mb bit before passing the xdp buffer to eBPF layer Lorenzo Bianconi
2021-09-20  8:25   ` Shay Agroskin
2021-09-20  8:37     ` Lorenzo Bianconi
2021-09-20  8:45       ` Shay Agroskin
2021-09-20  9:00         ` Lorenzo Bianconi
2021-09-10 16:14 ` [PATCH v14 bpf-next 04/18] net: mvneta: simplify mvneta_swbm_add_rx_fragment management Lorenzo Bianconi
2021-09-10 16:14 ` [PATCH v14 bpf-next 05/18] net: xdp: add xdp_update_skb_shared_info utility routine Lorenzo Bianconi
2021-09-10 16:14 ` [PATCH v14 bpf-next 06/18] net: marvell: rely on " Lorenzo Bianconi
2021-09-10 16:14 ` [PATCH v14 bpf-next 07/18] xdp: add multi-buff support to xdp_return_{buff/frame} Lorenzo Bianconi
2021-09-10 16:14 ` [PATCH v14 bpf-next 08/18] net: mvneta: add multi buffer support to XDP_TX Lorenzo Bianconi
2021-09-10 16:14 ` [PATCH v14 bpf-next 09/18] net: mvneta: enable jumbo frames for XDP Lorenzo Bianconi
2021-09-10 16:14 ` [PATCH v14 bpf-next 10/18] bpf: add multi-buff support to the bpf_xdp_adjust_tail() API Lorenzo Bianconi
2021-09-16 16:55   ` Jakub Kicinski
2021-09-17 10:02     ` Lorenzo Bianconi
2021-09-17 13:03       ` Jakub Kicinski
2021-09-10 16:14 ` [PATCH v14 bpf-next 11/18] bpf: introduce bpf_xdp_get_buff_len helper Lorenzo Bianconi
2021-09-10 16:14 ` [PATCH v14 bpf-next 12/18] bpf: add multi-buffer support to xdp copy helpers Lorenzo Bianconi
2021-09-10 16:14 ` [PATCH v14 bpf-next 13/18] bpf: move user_size out of bpf_test_init Lorenzo Bianconi
2021-09-10 16:14 ` [PATCH v14 bpf-next 14/18] bpf: introduce multibuff support to bpf_prog_test_run_xdp() Lorenzo Bianconi
2021-09-10 16:14 ` [PATCH v14 bpf-next 15/18] bpf: test_run: add xdp_shared_info pointer in bpf_test_finish signature Lorenzo Bianconi
2021-09-10 16:14 ` [PATCH v14 bpf-next 16/18] bpf: update xdp_adjust_tail selftest to include multi-buffer Lorenzo Bianconi
2021-09-10 16:14 ` [PATCH v14 bpf-next 17/18] net: xdp: introduce bpf_xdp_adjust_data helper Lorenzo Bianconi
2021-09-10 16:14 ` [PATCH v14 bpf-next 18/18] bpf: add bpf_xdp_adjust_data selftest Lorenzo Bianconi
2021-09-16 16:55 ` [PATCH v14 bpf-next 00/18] mvneta: introduce XDP multi-buffer support Jakub Kicinski
2021-09-17 14:51   ` Lorenzo Bianconi
2021-09-17 18:33     ` Jakub Kicinski
2021-09-17 18:43       ` Alexei Starovoitov
2021-09-17 19:00         ` Jakub Kicinski
2021-09-17 19:10           ` Alexei Starovoitov
2021-09-17 22:07             ` John Fastabend
2021-09-18 11:53               ` Toke Høiland-Jørgensen
2021-09-20 18:02                 ` Jakub Kicinski
2021-09-20 21:01                   ` Toke Høiland-Jørgensen
2021-09-20 21:25                     ` Jakub Kicinski
2021-09-20 22:44                       ` Toke Høiland-Jørgensen [this message]
2021-09-21 10:03                         ` Eelco Chaudron
2021-09-28 11:48                           ` Magnus Karlsson
2021-09-29 10:36                         ` Lorenz Bauer
2021-09-29 12:25                           ` Toke Høiland-Jørgensen
2021-09-29 12:32                             ` Lorenz Bauer
2021-09-29 17:48                             ` Jakub Kicinski
2021-09-29 17:46                           ` Jakub Kicinski
2021-09-29 10:41   ` Lorenz Bauer
2021-09-29 12:10     ` Toke Høiland-Jørgensen
2021-09-29 12:38       ` Lorenz Bauer
2021-09-29 18:54         ` Alexei Starovoitov
2021-09-29 19:22           ` Jakub Kicinski
2021-09-29 20:39             ` Toke Høiland-Jørgensen
2021-10-01  9:03               ` Lorenzo Bianconi
2021-10-01 18:35                 ` Jakub Kicinski
2021-10-06  9:32                   ` Lorenzo Bianconi
2021-10-06 10:08                     ` Eelco Chaudron
2021-10-06 12:15                       ` Lorenzo Bianconi

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