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From: "Song, Yoong Siang" <yoong.siang.song@intel.com>
To: Kurt Kanzenbach <kurt@linutronix.de>, "Bezdeka, Florian"
	<florian.bezdeka@siemens.com>, "Brandeburg, Jesse"
	<jesse.brandeburg@intel.com>, "Nguyen, Anthony L"
	<anthony.l.nguyen@intel.com>, "David S . Miller" <davem@davemloft.net>, "Eric
 Dumazet" <edumazet@google.com>, Jakub Kicinski <kuba@kernel.org>, Paolo Abeni
	<pabeni@redhat.com>, Richard Cochran <richardcochran@gmail.com>, "Alexei
 Starovoitov" <ast@kernel.org>, Daniel Borkmann <daniel@iogearbox.net>, Jesper
 Dangaard Brouer <hawk@kernel.org>, John Fastabend <john.fastabend@gmail.com>,
	Stanislav Fomichev <sdf@google.com>, "Gomes, Vinicius"
	<vinicius.gomes@intel.com>, "Fijalkowski, Maciej"
	<maciej.fijalkowski@intel.com>
CC: "intel-wired-lan@lists.osuosl.org" <intel-wired-lan@lists.osuosl.org>,
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	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"bpf@vger.kernel.org" <bpf@vger.kernel.org>, "xdp-hints@xdp-project.net"
	<xdp-hints@xdp-project.net>
Subject: RE: [xdp-hints] Re: [PATCH iwl-next,v4 1/1] igc: Add Tx hardware
 timestamp request for AF_XDP zero-copy packet
Thread-Topic: [xdp-hints] Re: [PATCH iwl-next,v4 1/1] igc: Add Tx hardware
 timestamp request for AF_XDP zero-copy packet
Thread-Index: AQHaf1vDcRX66gQlB0+gJtjiHFgRbLFJ/peAgAAUiKA=
Date: Tue, 26 Mar 2024 14:55:33 +0000
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References: <20240325020928.1987947-1-yoong.siang.song@intel.com>
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 <87h6gtb0p0.fsf@kurt.kurt.home>
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On Tuesday, March 26, 2024 9:08 PM, Kurt Kanzenbach <kurt@linutronix.de> wr=
ote:
>Hi Florian,
>
>On Tue Mar 26 2024, Florian Bezdeka wrote:
>> On Mon, 2024-03-25 at 10:09 +0800, Song Yoong Siang wrote:
>>> This patch adds support to per-packet Tx hardware timestamp request to
>>> AF_XDP zero-copy packet via XDP Tx metadata framework. Please note that
>>> user needs to enable Tx HW timestamp capability via igc_ioctl() with
>>> SIOCSHWTSTAMP cmd before sending xsk Tx hardware timestamp request.
>>>
>>> Same as implementation in RX timestamp XDP hints kfunc metadata, Timer =
0
>>> (adjustable clock) is used in xsk Tx hardware timestamp. i225/i226 have
>>> four sets of timestamping registers. *skb and *xsk_tx_buffer pointers
>>> are used to indicate whether the timestamping register is already occup=
ied.
>>
>> Let me make sure that I fully understand that: In my own words:
>>
>> With that applied I'm able to get the point in time from the device
>> when a specific frame made it to the wire. I have to enable that
>> functionality using the mentioned ioctl() call first, and then check
>> the meta area (located in the umem right before the frame payload)
>> while consuming the completion queue/ring. Correct?

Hi Florian,

Yes, you are right. But before you pass the frame to driver, make sure
you request Tx metadata hardware timestamp feature by setting
XDP_TXMD_FLAGS_TIMESTAMP flag.
You can refer to tools/testing/selftests/bpf/xdp_hw_metadata.c
on how to do it.=20

>>
>> If so, we now have a feedback channel for meta information for/from TX.
>> Are there any plans - or would it be possible - to support Earliest
>> TxTime First (NET_SCHED_ETF) QDisc based on that channel? In the past
>> we had the problem that we we're missing a feedback channel to
>> communicate back invalid lunch times.
>
>Just asking: How would that work? AFAIK XDP bypasses the Qdisc
>layer. Currently invalid Launch Times are accounted in the ETF Qdisc
>itself. Does that mean every driver has to take care of it?
>
>Thanks,
>Kurt

Florian & Kurt,

Yes, me and Stanislav are trying to add Earliest TxTime First / Launch Time=
 to the framework.
Please refer to [1] for the patchset. The metadata framework will just pass=
 the
Launch time value to driver, and driver need to handle the rest.
In the patchset, I am enabling it on stmmac driver only, but we need more d=
rivers
to check whether the design is feasible for different drivers, cause each d=
river is
having their own limitation on launch time. Therefore, after this tx hwts p=
atch accepted,
I will try to enable launch time on igc driver, and submit new version.=20

Kurt is right that current metadata framework is lacking a way to feedback =
whether
the launch time is invalid or not. Maybe we can try to enable launch time w=
ithout feedback,
then discuss about the status report design.

[1] https://patchwork.kernel.org/project/netdevbpf/cover/20231203165129.174=
0512-1-yoong.siang.song@intel.com/

Thanks & Regards
Siang