From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: brakmo <brakmo@fb.com>, netdev <netdev@vger.kernel.org>,
Martin Lau <kafai@fb.com>, Alexei Starovoitov <ast@fb.com>,
Daniel Borkmann <daniel@iogearbox.net>,
Kernel Team <Kernel-team@fb.com>
Subject: Re: [PATCH bpf-next 0/7] bpf: Propagate cn to TCP
Date: Sat, 23 Mar 2019 08:41:26 -0700 [thread overview]
Message-ID: <20190323154124.gorqpaqex7ihfs6d@ast-mbp> (raw)
In-Reply-To: <704cb63c-13cd-f0ed-d546-18e3596bb63d@gmail.com>
On Sat, Mar 23, 2019 at 02:12:39AM -0700, Eric Dumazet wrote:
>
>
> On 03/23/2019 01:05 AM, brakmo wrote:
> > This patchset adds support for propagating congestion notifications (cn)
> > to TCP from cgroup inet skb egress BPF programs.
> >
> > Current cgroup skb BPF programs cannot trigger TCP congestion window
> > reductions, even when they drop a packet. This patch-set adds support
> > for cgroup skb BPF programs to send congestion notifications in the
> > return value when the packets are TCP packets. Rather than the
> > current 1 for keeping the packet and 0 for dropping it, they can
> > now return:
> > NET_XMIT_SUCCESS (0) - continue with packet output
> > NET_XMIT_DROP (1) - drop packet and do cn
> > NET_XMIT_CN (2) - continue with packet output and do cn
> > -EPERM - drop packet
> >
>
> I believe I already mentioned this model is broken, if you have any virtual
> device before the cgroup BPF program.
>
> Please think about offloading the pacing/throttling in the NIC,
> there is no way we will report back to tcp stack instant notifications.
I don't think 'offload to google proprietary nic' is a suggestion
that folks can practically follow.
Very few NICs can offload pacing to hw and there are plenty of limitations.
This patch set represents a pure sw solution that works and scales to millions of flows.
> This patch series is going way too far for my taste.
I would really appreciate if you can do a technical review of the patches.
Our previous approach didn't quite work due to complexity around locked/non-locked socket.
This is a cleaner approach.
Either we go with this one or will add a bpf hook into __tcp_transmit_skb.
This approach is better since it works for other protocols and can be
used by qdiscs w/o any bpf.
> This idea is not new, you were at Google when it was experimented by Nandita and
> others, and we know it is not worth the pain.
google networking needs are different from the rest of the world.
Thank you.
next prev parent reply other threads:[~2019-03-23 15:41 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-23 8:05 [PATCH bpf-next 0/7] bpf: Propagate cn to TCP brakmo
2019-03-23 8:05 ` [PATCH bpf-next 1/7] bpf: Create BPF_PROG_CGROUP_INET_EGRESS_RUN_ARRAY brakmo
2019-03-23 8:05 ` [PATCH bpf-next 2/7] bpf: cgroup inet skb programs can return 0 to 3 brakmo
2019-03-23 8:05 ` [PATCH bpf-next 3/7] bpf: Update __cgroup_bpf_run_filter_skb with cn brakmo
2019-03-23 8:05 ` [PATCH bpf-next 4/7] bpf: Update BPF_CGROUP_RUN_PROG_INET_EGRESS calls brakmo
2019-03-23 8:05 ` [PATCH bpf-next 5/7] bpf: sysctl for probe_on_drop brakmo
2019-03-23 8:05 ` [PATCH bpf-next 6/7] bpf: Add cn support to hbm_out_kern.c brakmo
2019-03-23 8:05 ` [PATCH bpf-next 7/7] bpf: Add more stats to HBM brakmo
2019-03-23 9:12 ` [PATCH bpf-next 0/7] bpf: Propagate cn to TCP Eric Dumazet
2019-03-23 15:41 ` Alexei Starovoitov [this message]
2019-03-24 5:36 ` Eric Dumazet
2019-03-24 16:19 ` Alexei Starovoitov
2019-03-25 8:33 ` Eric Dumazet
2019-03-25 8:48 ` Eric Dumazet
2019-03-26 4:27 ` Alexei Starovoitov
2019-03-26 8:06 ` Eric Dumazet
2019-03-26 15:07 ` Alexei Starovoitov
2019-03-26 15:43 ` Eric Dumazet
2019-03-26 17:01 ` Alexei Starovoitov
2019-03-26 18:07 ` Eric Dumazet
2019-03-26 8:13 ` Eric Dumazet
2019-03-24 5:48 ` Eric Dumazet
2019-03-24 1:14 ` Lawrence Brakmo
2019-03-24 5:58 ` Eric Dumazet
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