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From: "Toke Høiland-Jørgensen" <toke@redhat.com>
To: Lorenzo Bianconi <lorenzo@kernel.org>
Cc: Jakub Kicinski <kuba@kernel.org>,
	bpf@vger.kernel.org, netdev@vger.kernel.org,
	lorenzo.bianconi@redhat.com, davem@davemloft.net, ast@kernel.org,
	daniel@iogearbox.net, shayagr@amazon.com,
	john.fastabend@gmail.com, dsahern@kernel.org, brouer@redhat.com,
	echaudro@redhat.com, jasowang@redhat.com,
	alexander.duyck@gmail.com, saeed@kernel.org,
	maciej.fijalkowski@intel.com, magnus.karlsson@intel.com,
	tirthendu.sarkar@intel.com
Subject: Re: [PATCH v17 bpf-next 12/23] bpf: add multi-buff support to the bpf_xdp_adjust_tail() API
Date: Mon, 08 Nov 2021 21:46:59 +0100	[thread overview]
Message-ID: <87a6ieqssc.fsf@toke.dk> (raw)
In-Reply-To: <YYl1P+nPSuMjI+e6@lore-desk>

Lorenzo Bianconi <lorenzo@kernel.org> writes:

>> Lorenzo Bianconi <lorenzo@kernel.org> writes:
>> 
>> >> On Thu,  4 Nov 2021 18:35:32 +0100 Lorenzo Bianconi wrote:
>> >> > This change adds support for tail growing and shrinking for XDP multi-buff.
>> >> > 
>> >> > When called on a multi-buffer packet with a grow request, it will always
>> >> > work on the last fragment of the packet. So the maximum grow size is the
>> >> > last fragments tailroom, i.e. no new buffer will be allocated.
>> >> > 
>> >> > When shrinking, it will work from the last fragment, all the way down to
>> >> > the base buffer depending on the shrinking size. It's important to mention
>> >> > that once you shrink down the fragment(s) are freed, so you can not grow
>> >> > again to the original size.
>> >> 
>> >> > +static int bpf_xdp_mb_increase_tail(struct xdp_buff *xdp, int offset)
>> >> > +{
>> >> > +	struct skb_shared_info *sinfo = xdp_get_shared_info_from_buff(xdp);
>> >> > +	skb_frag_t *frag = &sinfo->frags[sinfo->nr_frags - 1];
>> >> > +	int size, tailroom;
>> >> > +
>> >> > +	tailroom = xdp->frame_sz - skb_frag_size(frag) - skb_frag_off(frag);
>> >> 
>> >> I know I complained about this before but the assumption that we can
>> >> use all the space up to xdp->frame_sz makes me uneasy.
>> >> 
>> >> Drivers may not expect the idea that core may decide to extend the 
>> >> last frag.. I don't think the skb path would ever do this.
>> >> 
>> >> How do you feel about any of these options: 
>> >>  - dropping this part for now (return an error for increase)
>> >>  - making this an rxq flag or reading the "reserved frag size"
>> >>    from rxq (so that drivers explicitly opt-in)
>> >>  - adding a test that can be run on real NICs
>> >> ?
>> >
>> > I think this has been added to be symmetric with bpf_xdp_adjust_tail().
>> > I do think there is a real use-case for it so far so I am fine to just
>> > support the shrink part.
>> >
>> > @Eelco, Jesper, Toke: any comments on it?
>> 
>> Well, tail adjust is useful for things like encapsulations that need to
>> add a trailer. Don't see why that wouldn't be something people would
>> want to do for jumboframes as well?
>> 
>
> I agree this would be useful for protocols that add a trailer.
>
>> Not sure I get what the issue is with this either? But having a test
>> that can be run to validate this on hardware would be great in any case,
>> I suppose - we've been discussing more general "compliance tests" for
>> XDP before...
>
> what about option 2? We can add a frag_size field to rxq [0] that is set by
> the driver initializing the xdp_buff. frag_size set to 0 means we can use
> all the buffer.
>
> Regards,
> Lorenzo
>
> [0] pahole -C xdp_rxq_info vmlinux
> struct xdp_rxq_info {
> 	struct net_device *        dev;                  /*     0     8 */
> 	u32                        queue_index;          /*     8     4 */
> 	u32                        reg_state;            /*    12     4 */
> 	struct xdp_mem_info        mem;                  /*    16     8 */
> 	unsigned int               napi_id;              /*    24     4 */
>
> 	/* size: 64, cachelines: 1, members: 5 */
> 	/* padding: 36 */
> } __attribute__((__aligned__(64)));

Works for me :)

-Toke


  reply	other threads:[~2021-11-08 20:47 UTC|newest]

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-11-04 17:35 [PATCH v17 bpf-next 00/23] mvneta: introduce XDP multi-buffer support Lorenzo Bianconi
2021-11-04 17:35 ` [PATCH v17 bpf-next 01/23] net: skbuff: add size metadata to skb_shared_info for xdp Lorenzo Bianconi
2021-11-04 17:35 ` [PATCH v17 bpf-next 02/23] xdp: introduce flags field in xdp_buff/xdp_frame Lorenzo Bianconi
2021-11-04 17:35 ` [PATCH v17 bpf-next 03/23] net: mvneta: update mb bit before passing the xdp buffer to eBPF layer Lorenzo Bianconi
2021-11-04 17:35 ` [PATCH v17 bpf-next 04/23] net: mvneta: simplify mvneta_swbm_add_rx_fragment management Lorenzo Bianconi
2021-11-04 17:35 ` [PATCH v17 bpf-next 05/23] net: xdp: add xdp_update_skb_shared_info utility routine Lorenzo Bianconi
2021-11-04 17:35 ` [PATCH v17 bpf-next 06/23] net: marvell: rely on " Lorenzo Bianconi
2021-11-04 17:35 ` [PATCH v17 bpf-next 07/23] xdp: add multi-buff support to xdp_return_{buff/frame} Lorenzo Bianconi
2021-11-04 17:35 ` [PATCH v17 bpf-next 08/23] net: mvneta: add multi buffer support to XDP_TX Lorenzo Bianconi
2021-11-04 17:35 ` [PATCH v17 bpf-next 09/23] bpf: introduce BPF_F_XDP_MB flag in prog_flags loading the ebpf program Lorenzo Bianconi
2021-11-04 17:35 ` [PATCH v17 bpf-next 10/23] net: mvneta: enable jumbo frames if the loaded XDP program support mb Lorenzo Bianconi
2021-11-04 17:35 ` [PATCH v17 bpf-next 11/23] bpf: introduce bpf_xdp_get_buff_len helper Lorenzo Bianconi
2021-11-04 17:35 ` [PATCH v17 bpf-next 12/23] bpf: add multi-buff support to the bpf_xdp_adjust_tail() API Lorenzo Bianconi
2021-11-05  2:16   ` Jakub Kicinski
2021-11-05 13:57     ` Lorenzo Bianconi
2021-11-05 23:29   ` Jakub Kicinski
2021-11-08 16:55     ` Lorenzo Bianconi
2021-11-08 18:08       ` Toke Høiland-Jørgensen
2021-11-08 19:06         ` Lorenzo Bianconi
2021-11-08 20:46           ` Toke Høiland-Jørgensen [this message]
2021-11-08 21:40           ` Jakub Kicinski
2021-11-09 21:58             ` Lorenzo Bianconi
2021-11-04 17:35 ` [PATCH v17 bpf-next 13/23] bpf: add multi-buffer support to xdp copy helpers Lorenzo Bianconi
2021-11-05 23:29   ` Jakub Kicinski
2021-11-08 13:59     ` Lorenzo Bianconi
2021-11-11  7:50       ` Eelco Chaudron
2021-11-04 17:35 ` [PATCH v17 bpf-next 14/23] bpf: move user_size out of bpf_test_init Lorenzo Bianconi
2021-11-04 17:35 ` [PATCH v17 bpf-next 15/23] bpf: introduce multibuff support to bpf_prog_test_run_xdp() Lorenzo Bianconi
2021-11-04 17:35 ` [PATCH v17 bpf-next 16/23] bpf: test_run: add xdp_shared_info pointer in bpf_test_finish signature Lorenzo Bianconi
2021-11-04 17:35 ` [PATCH v17 bpf-next 17/23] bpf: selftests: update xdp_adjust_tail selftest to include multi-buffer Lorenzo Bianconi
2021-11-04 17:35 ` [PATCH v17 bpf-next 18/23] libbpf: Add SEC name for xdp_mb programs Lorenzo Bianconi
2021-11-04 17:35 ` [PATCH v17 bpf-next 19/23] bpf: generalise tail call map Lorenzo Bianconi
2021-11-04 17:35 ` [PATCH v17 bpf-next 20/23] net: xdp: introduce bpf_xdp_pointer utility routine Lorenzo Bianconi
2021-11-05 23:29   ` Jakub Kicinski
2021-11-08 16:48     ` Lorenzo Bianconi
2021-11-04 17:35 ` [PATCH v17 bpf-next 21/23] bpf: selftests: introduce bpf_xdp_{load,store}_bytes selftest Lorenzo Bianconi
2021-11-04 17:35 ` [PATCH v17 bpf-next 22/23] bpf: selftests: add CPUMAP/DEVMAP selftests for xdp multi-buff Lorenzo Bianconi
2021-11-04 17:35 ` [PATCH v17 bpf-next 23/23] xdp: disable XDP_REDIRECT " Lorenzo Bianconi

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