From: John Fastabend <john.fastabend@gmail.com>
To: Lorenzo Bianconi <lorenzo@kernel.org>,
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: Mon, 05 Oct 2020 21:29:36 -0700 [thread overview]
Message-ID: <5f7bf2b0bf899_4f19a2083f@john-XPS-13-9370.notmuch> (raw)
In-Reply-To: <20201005222454.GB3501@localhost.localdomain>
Lorenzo Bianconi wrote:
> [...]
>
> >
> > 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.
I agree. We could also only populate the fields if the program accesses
the fields.
> 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.
Seems interesting, might be a good idea.
> 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?
I don't see an easy way, but also this series doesn't have the data
access support.
Its hard to tell until we get at least a 40gbps nic if my concern about
performance is real or not. Prefetching smartly could resolve some of the
issue I guess.
If the Intel folks are working on it I think waiting would be great. Otherwise
at minimum drop the helpers and be prepared to revert things if needed.
>
> > - 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
next prev parent reply other threads:[~2020-10-06 4:29 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
2020-10-06 4:29 ` John Fastabend [this message]
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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