Re: AF_XDP metadata/hints

From: Jesper Dangaard Brouer <brouer@redhat.com>
To: John Fastabend <john.fastabend@gmail.com>
Cc: "Alexander Lobakin" <alexandr.lobakin@intel.com>,
	"Toke Høiland-Jørgensen" <toke@redhat.com>,
	"Saeed Mahameed" <saeed@kernel.org>,
	"Raczynski, Piotr" <piotr.raczynski@intel.com>,
	"Zhang, Jessica" <jessica.zhang@intel.com>,
	"Kubiak, Marcin" <marcin.kubiak@intel.com>,
	"Joseph, Jithu" <jithu.joseph@intel.com>,
	"kurt@linutronix.de" <kurt@linutronix.de>,
	"Maloor, Kishen" <kishen.maloor@intel.com>,
	"Gomes, Vinicius" <vinicius.gomes@intel.com>,
	"Brandeburg, Jesse" <jesse.brandeburg@intel.com>,
	"Swiatkowski, Michal" <michal.swiatkowski@intel.com>,
	"Plantykow, Marta A" <marta.a.plantykow@intel.com>,
	"Ong, Boon Leong" <boon.leong.ong@intel.com>,
	"Desouza, Ederson" <ederson.desouza@intel.com>,
	"Song, Yoong Siang" <yoong.siang.song@intel.com>,
	"Czapnik, Lukasz" <lukasz.czapnik@intel.com>,
	bpf@vger.kernel.org, brouer@redhat.com
Subject: Re: AF_XDP metadata/hints
Date: Wed, 26 May 2021 13:49:10 +0200	[thread overview]
Message-ID: <20210526134910.1c06c5d8@carbon> (raw)
In-Reply-To: <60add3cad4ef0_3b75f2086@john-XPS-13-9370.notmuch>

On Tue, 25 May 2021 21:51:22 -0700
John Fastabend <john.fastabend@gmail.com> wrote:

> Separate the config of hardware from the BPF infrastructure these
> are two separate things.

I fully agree.

How should we handle existing config interfaces?

Let me give some concrete examples. Today there are multiple existing
interfaces to enable/disable NIC hardware features that change what is
available to put in our BTF-layout.

E.g. changing if VLAN is in descriptor:
 # ethtool -K ixgbe1 rx-vlan-offload off
 # ethtool -k ixgbe1 | grep vlan-offload
 rx-vlan-offload: off
 tx-vlan-offload: on

The timestamping features can be listed by ethtool -T (see below
signature), but it is a socket option that enable[1] these
(see SO_TIMESTAMPNS or SOF_TIMESTAMPING_RX_HARDWARE).

Or tuning RSS hash fields:
 [2] https://github.com/stackpath/rxtxcpu/blob/master/Documentation/case-studies/observing-rss-on-ixgbe-advanced-rss-configuration-rss-hash-fields.md

I assume we need to stay compatible and respect the existing config
interfaces, right?

Should we simple leverage existing interfaces?

E.g. tcpdump --time-stamp-type=adapter_unsynced could simple enable the
BTF-layout that contains the RX-timestamp.  This would make it avail to
XDP/AF_XDP and the xdp_frame can also create a SKB with the timestamp.

[1] https://www.kernel.org/doc/html/latest/networking/timestamping.html
-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer

# ethtool -T ixgbe1
Time stamping parameters for ixgbe1:
Capabilities:
	hardware-transmit
	software-transmit
	hardware-receive
	software-receive
	software-system-clock
	hardware-raw-clock
PTP Hardware Clock: 7
Hardware Transmit Timestamp Modes:
	off
	on
Hardware Receive Filter Modes:
	none
	ptpv1-l4-sync
	ptpv1-l4-delay-req
	ptpv2-event

# ethtool -T igc1
Time stamping parameters for igc1:
Capabilities:
	hardware-transmit
	software-transmit
	hardware-receive
	software-receive
	software-system-clock
	hardware-raw-clock
PTP Hardware Clock: 1
Hardware Transmit Timestamp Modes:
	off
	on
Hardware Receive Filter Modes:
	none
	all