From: Jesper Dangaard Brouer <brouer@redhat.com>
To: "Toke Høiland-Jørgensen" <toke@redhat.com>
Cc: "Jakub Kicinski" <kuba@kernel.org>,
"David Ahern" <dsahern@gmail.com>,
"David Ahern" <dsahern@kernel.org>,
netdev@vger.kernel.org, prashantbhole.linux@gmail.com,
jasowang@redhat.com, davem@davemloft.net, mst@redhat.com,
toshiaki.makita1@gmail.com, daniel@iogearbox.net,
john.fastabend@gmail.com, ast@kernel.org, kafai@fb.com,
songliubraving@fb.com, yhs@fb.com, andriin@fb.com,
"David Ahern" <dahern@digitalocean.com>,
brouer@redhat.com, "Björn Töpel" <bjorn.topel@intel.com>,
"Karlsson, Magnus" <magnus.karlsson@intel.com>
Subject: Re: [PATCH bpf-next 03/12] net: Add IFLA_XDP_EGRESS for XDP programs in the egress path
Date: Mon, 3 Feb 2020 23:15:03 +0100 [thread overview]
Message-ID: <20200203231503.24eec7f0@carbon> (raw)
In-Reply-To: <87zhdzbfa3.fsf@toke.dk>
On Mon, 03 Feb 2020 21:13:24 +0100
Toke Høiland-Jørgensen <toke@redhat.com> wrote:
> Oops, I see I forgot to reply to this bit:
>
> >> Yeah, but having the low-level details available to the XDP program
> >> (such as HW queue occupancy for the egress hook) is one of the benefits
> >> of XDP, isn't it?
> >
> > I think I glossed over the hope for having access to HW queue occupancy
> > - what exactly are you after?
> >
> > I don't think one can get anything beyond a BQL type granularity.
> > Reading over PCIe is out of question, device write back on high
> > granularity would burn through way too much bus throughput.
>
> This was Jesper's idea originally, so maybe he can explain better; but
> as I understood it, he basically wanted to expose the same information
> that BQL has to eBPF. Making it possible for an eBPF program to either
> (re-)implement BQL with its own custom policy, or react to HWQ pressure
> in some other way, such as by load balancing to another interface.
Yes, and I also have plans that goes beyond BQL. But let me start with
explaining the BQL part, and answer Toke's question below.
On Mon, 03 Feb 2020 20:56:03 +0100 Toke wrote:
> [...] Hmm, I wonder if a TX driver hook is enough?
Short answer is no, a TX driver hook is not enough. The queue state
info the TX driver hook have access to, needs to be updated once the
hardware have "confirmed" the TX-DMA operation have completed. For
BQL/DQL this update happens during TX-DMA completion/cleanup (code
see call sites for netdev_tx_completed_queue()). (As Jakub wisely
point out we cannot query the device directly due to performance
implications). It doesn't need to be a new BPF hook, just something
that update the queue state info (we could piggy back on the
netdev_tx_completed_queue() call or give TX hook access to
dev_queue->dql).
Regarding "where is the queue": For me the XDP-TX queue is the NIC
hardware queue, that this BPF hook have some visibility into and can do
filtering on. (Imagine that my TX queue is bandwidth limited, then I
can shrink the packet size and still send a "congestion" packet to my
receiver).
The bigger picture is that I envision the XDP-TX/egress hook can
open-up for taking advantage of NIC hardware TX queue features.
This also ties into the queue abstraction work by Björn+Magnus.
Today NIC hardware can do a million TX-queues, and hardware can also do
rate limiting per queue. Thus, I also envision that the XDP-TX/egress
hook can choose/change the TX queue the packet is queue/sent on (we can
likely just overload the XDP_REDIRECT and have a new bpf map type for
this).
--
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:[~2020-02-03 22:15 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-23 1:41 [PATCH bpf-next 00/12] Add support for XDP in egress path David Ahern
2020-01-23 1:41 ` [PATCH bpf-next 01/12] net: Add new XDP setup and query commands David Ahern
2020-01-23 1:42 ` [PATCH bpf-next 02/12] net: Add BPF_XDP_EGRESS as a bpf_attach_type David Ahern
2020-01-23 11:34 ` Toke Høiland-Jørgensen
2020-01-23 21:32 ` David Ahern
2020-01-24 9:49 ` Toke Høiland-Jørgensen
2020-01-24 7:33 ` Martin Lau
2020-01-23 1:42 ` [PATCH bpf-next 03/12] net: Add IFLA_XDP_EGRESS for XDP programs in the egress path David Ahern
2020-01-23 11:35 ` Toke Høiland-Jørgensen
2020-01-23 21:33 ` David Ahern
2020-01-24 15:21 ` Jakub Kicinski
2020-01-24 15:36 ` Toke Høiland-Jørgensen
2020-01-26 1:43 ` David Ahern
2020-01-26 4:54 ` Alexei Starovoitov
2020-02-02 17:59 ` David Ahern
2020-01-26 12:49 ` Jesper Dangaard Brouer
2020-01-26 16:38 ` David Ahern
2020-01-26 22:17 ` Jakub Kicinski
2020-01-28 14:13 ` Jesper Dangaard Brouer
2020-01-30 14:45 ` Jakub Kicinski
2020-02-01 16:03 ` Toke Høiland-Jørgensen
2020-02-02 17:48 ` David Ahern
2020-01-26 22:11 ` Jakub Kicinski
2020-01-27 4:03 ` David Ahern
2020-01-27 14:16 ` Jakub Kicinski
2020-01-28 3:43 ` David Ahern
2020-01-28 13:57 ` Jakub Kicinski
2020-02-01 16:24 ` Toke Høiland-Jørgensen
2020-02-01 17:08 ` Jakub Kicinski
2020-02-01 20:05 ` Toke Høiland-Jørgensen
2020-02-02 4:15 ` Jakub Kicinski
2020-02-03 19:56 ` Toke Høiland-Jørgensen
2020-02-03 20:13 ` Toke Høiland-Jørgensen
2020-02-03 22:15 ` Jesper Dangaard Brouer [this message]
2020-02-04 11:00 ` Toke Høiland-Jørgensen
2020-02-04 17:09 ` Jakub Kicinski
2020-02-05 15:30 ` Toke Høiland-Jørgensen
2020-02-02 17:45 ` David Ahern
2020-02-02 19:12 ` Jakub Kicinski
2020-02-02 17:43 ` David Ahern
2020-02-02 19:31 ` Jakub Kicinski
2020-02-02 21:51 ` David Ahern
2020-02-01 15:59 ` Toke Høiland-Jørgensen
2020-02-02 17:54 ` David Ahern
2020-02-03 20:09 ` Toke Høiland-Jørgensen
2020-01-23 1:42 ` [PATCH bpf-next 04/12] net: core: rename netif_receive_generic_xdp() to do_generic_xdp_core() David Ahern
2020-01-23 1:42 ` [PATCH bpf-next 05/12] tuntap: check tun_msg_ctl type at necessary places David Ahern
2020-01-23 1:42 ` [PATCH bpf-next 06/12] tun: move shared functions to if_tun.h David Ahern
2020-01-23 1:42 ` [PATCH bpf-next 07/12] vhost_net: user tap recvmsg api to access ptr ring David Ahern
2020-01-23 8:26 ` Michael S. Tsirkin
2020-01-23 1:42 ` [PATCH bpf-next 08/12] tuntap: remove usage of ptr ring in vhost_net David Ahern
2020-01-23 1:42 ` [PATCH bpf-next 09/12] tun: set egress XDP program David Ahern
2020-01-23 1:42 ` [PATCH bpf-next 10/12] tun: run XDP program in tx path David Ahern
2020-01-23 8:23 ` Michael S. Tsirkin
2020-01-24 13:36 ` Prashant Bhole
2020-01-24 13:44 ` Prashant Bhole
2020-01-23 1:42 ` [PATCH bpf-next 11/12] libbpf: Add egress XDP support David Ahern
2020-01-23 1:42 ` [PATCH bpf-next 12/12] samples/bpf: xdp1, add " David Ahern
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