From: Lorenzo Bianconi <lorenzo@kernel.org>
To: John Fastabend <john.fastabend@gmail.com>
Cc: Jesper Dangaard Brouer <brouer@redhat.com>,
Lorenzo Bianconi <lorenzo.bianconi@redhat.com>,
bpf@vger.kernel.org, netdev@vger.kernel.org, davem@davemloft.net,
kuba@kernel.org, ast@kernel.org, daniel@iogearbox.net,
shayagr@amazon.com, sameehj@amazon.com, dsahern@kernel.org,
echaudro@redhat.com
Subject: Re: [PATCH v4 bpf-next 00/13] mvneta: introduce XDP multi-buffer support
Date: Tue, 6 Oct 2020 00:24:54 +0200 [thread overview]
Message-ID: <20201005222454.GB3501@localhost.localdomain> (raw)
In-Reply-To: <5f7b8e7a5ebfc_4f19a208ba@john-XPS-13-9370.notmuch>
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[...]
>
> In general I see no reason to populate these fields before the XDP
> program runs. Someone needs to convince me why having frags info before
> program runs is useful. In general headers should be preserved and first
> frag already included in the data pointers. If users start parsing further
> they might need it, but this series doesn't provide a way to do that
> so IMO without those helpers its a bit difficult to debate.
We need to populate the skb_shared_info before running the xdp program in order to
allow the ebpf sanbox to access this data. If we restrict the access to the first
buffer only I guess we can avoid to do that but I think there is a value allowing
the xdp program to access this data.
A possible optimization can be access the shared_info only once before running
the ebpf program constructing the shared_info using a struct allocated on the
stack.
Moreover we can define a "xdp_shared_info" struct to alias the skb_shared_info
one in order to have most on frags elements in the first "shared_info" cache line.
>
> Specifically for XDP_TX case we can just flip the descriptors from RX
> ring to TX ring and keep moving along. This is going to be ideal on
> 40/100Gbps nics.
>
> I'm not arguing that its likely possible to put some prefetch logic
> in there and keep the pipe full, but I would need to see that on
> a 100gbps nic to be convinced the details here are going to work. Or
> at minimum a 40gbps nic.
>
> >
> >
[...]
> Not against it, but these things are a bit tricky. Couple things I still
> want to see/understand
>
> - Lets see a 40gbps use a prefetch and verify it works in practice
> - Explain why we can't just do this after XDP program runs
how can we allow the ebpf program to access paged data if we do not do that?
> - How will we read data in the frag list if we need to parse headers
> inside the frags[].
>
> The above would be best to answer now rather than later IMO.
>
> Thanks,
> John
Regards,
Lorenzo
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next prev parent reply other threads:[~2020-10-05 22:25 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-02 14:41 [PATCH v4 bpf-next 00/13] mvneta: introduce XDP multi-buffer support Lorenzo Bianconi
2020-10-02 14:41 ` [PATCH v4 bpf-next 01/13] xdp: introduce mb in xdp_buff/xdp_frame Lorenzo Bianconi
2020-10-02 14:42 ` [PATCH v4 bpf-next 02/13] xdp: initialize xdp_buff mb bit to 0 in all XDP drivers Lorenzo Bianconi
2020-10-02 14:42 ` [PATCH v4 bpf-next 03/13] net: mvneta: update mb bit before passing the xdp buffer to eBPF layer Lorenzo Bianconi
2020-10-02 14:42 ` [PATCH v4 bpf-next 04/13] xdp: add multi-buff support to xdp_return_{buff/frame} Lorenzo Bianconi
2020-10-02 14:42 ` [PATCH v4 bpf-next 05/13] net: mvneta: add multi buffer support to XDP_TX Lorenzo Bianconi
2020-10-02 14:42 ` [PATCH v4 bpf-next 06/13] bpf: introduce bpf_xdp_get_frags_{count, total_size} helpers Lorenzo Bianconi
2020-10-02 15:36 ` John Fastabend
2020-10-02 16:25 ` Lorenzo Bianconi
2020-10-02 14:42 ` [PATCH v4 bpf-next 07/13] samples/bpf: add bpf program that uses xdp mb helpers Lorenzo Bianconi
2020-10-02 14:42 ` [PATCH v4 bpf-next 08/13] bpf: move user_size out of bpf_test_init Lorenzo Bianconi
2020-10-02 14:42 ` [PATCH v4 bpf-next 09/13] bpf: introduce multibuff support to bpf_prog_test_run_xdp() Lorenzo Bianconi
2020-10-08 8:06 ` Shay Agroskin
2020-10-08 10:46 ` Jesper Dangaard Brouer
2020-10-02 14:42 ` [PATCH v4 bpf-next 10/13] bpf: test_run: add skb_shared_info pointer in bpf_test_finish signature Lorenzo Bianconi
2020-10-02 14:42 ` [PATCH v4 bpf-next 11/13] bpf: add xdp multi-buffer selftest Lorenzo Bianconi
2020-10-02 14:42 ` [PATCH v4 bpf-next 12/13] net: mvneta: enable jumbo frames for XDP Lorenzo Bianconi
2020-10-02 14:42 ` [PATCH v4 bpf-next 13/13] bpf: cpumap: introduce xdp multi-buff support Lorenzo Bianconi
2020-10-02 15:25 ` [PATCH v4 bpf-next 00/13] mvneta: introduce XDP multi-buffer support John Fastabend
2020-10-02 16:06 ` Lorenzo Bianconi
2020-10-02 18:06 ` John Fastabend
2020-10-05 9:52 ` Jesper Dangaard Brouer
2020-10-05 21:22 ` John Fastabend
2020-10-05 22:24 ` Lorenzo Bianconi [this message]
2020-10-06 4:29 ` John Fastabend
2020-10-06 7:30 ` Jesper Dangaard Brouer
2020-10-06 15:28 ` Lorenzo Bianconi
2020-10-08 14:38 ` John Fastabend
2020-10-02 19:53 ` Daniel Borkmann
2020-10-05 15:50 ` Tirthendu Sarkar
2020-10-06 12:39 ` Jubran, Samih
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