From: John Fastabend <john.fastabend@gmail.com>
To: Lorenzo Bianconi <lorenzo.bianconi@redhat.com>,
Jesper Dangaard Brouer <brouer@redhat.com>
Cc: "John Fastabend" <john.fastabend@gmail.com>,
"Lorenzo Bianconi" <lorenzo@kernel.org>,
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,
"Eelco Chaudron" <echaudro@redhat.com>,
"Tirthendu Sarkar" <tirtha@gmail.com>,
"Toke Høiland-Jørgensen" <toke@redhat.com>
Subject: Re: [PATCH v4 bpf-next 00/13] mvneta: introduce XDP multi-buffer support
Date: Thu, 08 Oct 2020 07:38:50 -0700 [thread overview]
Message-ID: <5f7f247acf860_2007208c9@john-XPS-13-9370.notmuch> (raw)
In-Reply-To: <20201006152845.GC43823@lore-desk>
Lorenzo Bianconi wrote:
> > On Mon, 05 Oct 2020 21:29:36 -0700
> > John Fastabend <john.fastabend@gmail.com> wrote:
> >
> > > 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.
> >
> > Notice, a driver will not initialize/use the shared_info area unless
> > there are more segments. And (we have already established) the xdp->mb
> > bit is guarding BPF-prog from accessing shared_info area.
> >
> > > > 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.
> >
> > It *might* be a good idea ("alloc" shared_info on stack), but we should
> > benchmark this. The prefetch trick might be fast enough. But also
> > keep in mind the performance target, as with large size frames the
> > packet-per-sec we need to handle dramatically drop.
>
> right. I guess we need to define a workload we want to run for the
> xdp multi-buff use-case (e.g. if MTU is 9K we will have ~3 frames
> for each packets and # of pps will be much slower)
Right. Or configuring header split which would give 2 buffers with a much
smaller packet size. This would give some indication of the overhead. Then
we would likely want to look at XDP_TX and XDP_REDIRECT cases. At least
those would be my use cases.
>
> >
> >
>
> [...]
>
> >
> > I do think it makes sense to drop the helpers for now, and focus on how
> > this new multi-buffer frame type is handled in the existing code, and do
> > some benchmarking on higher speed NIC, before the BPF-helper start to
> > lockdown/restrict what we can change/revert as they define UAPI.
>
> ack, I will drop them in v5.
>
> Regards,
> Lorenzo
>
> >
> > E.g. existing code that need to handle this is existing helper
> > bpf_xdp_adjust_tail, which is something I have broad up before and even
> > described in[1]. Lets make sure existing code works with proposed
> > design, before introducing new helpers (and this makes it easier to
> > revert).
> >
> > [1] https://github.com/xdp-project/xdp-project/blob/master/areas/core/xdp-multi-buffer01-design.org#xdp-tail-adjust
> > --
> > Best regards,
> > Jesper Dangaard Brouer
> > MSc.CS, Principal Kernel Engineer at Red Hat
> > LinkedIn: http://www.linkedin.com/in/brouer
> >
next prev parent reply other threads:[~2020-10-08 14:39 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
2020-10-06 7:30 ` Jesper Dangaard Brouer
2020-10-06 15:28 ` Lorenzo Bianconi
2020-10-08 14:38 ` John Fastabend [this message]
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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