linux-kernel - Re: [PATCH RFC v2 1/6] ethtool: add interface to read Tx hardware timestamping statistics

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Date: Thu, 14 Mar 2024 11:48:11 -0700
From: Rahul Rameshbabu <rrameshbabu@...dia.com>
To: "Keller, Jacob E" <jacob.e.keller@...el.com>
Cc: Jakub Kicinski <kuba@...nel.org>, "Zaki, Ahmed" <ahmed.zaki@...el.com>,
 "Lobakin, Aleksander" <aleksander.lobakin@...el.com>,
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 <wojciech.drewek@...el.com>
Subject: Re: [PATCH RFC v2 1/6] ethtool: add interface to read Tx hardware
 timestamping statistics


On Thu, 14 Mar, 2024 17:50:10 +0000 "Keller, Jacob E" <jacob.e.keller@...el.com> wrote:
>> -----Original Message-----
>> From: Jakub Kicinski <kuba@...nel.org>
>> Sent: Wednesday, March 13, 2024 6:40 PM
>> To: Rahul Rameshbabu <rrameshbabu@...dia.com>
>> Cc: Zaki, Ahmed <ahmed.zaki@...el.com>; Lobakin, Aleksander
>> <aleksander.lobakin@...el.com>; alexandre.torgue@...s.st.com;
>> andrew@...n.ch; corbet@....net; davem@...emloft.net; dtatulea@...dia.com;
>> edumazet@...gle.com; gal@...dia.com; hkallweit1@...il.com; Keller, Jacob E
>> <jacob.e.keller@...el.com>; jiri@...nulli.us; joabreu@...opsys.com;
>> justinstitt@...gle.com; kory.maincent@...tlin.com; leon@...nel.org; linux-
>> doc@...r.kernel.org; linux-kernel@...r.kernel.org; liuhangbin@...il.com;
>> maxime.chevallier@...tlin.com; netdev@...r.kernel.org; pabeni@...hat.com;
>> Greenwalt, Paul <paul.greenwalt@...el.com>; Kitszel, Przemyslaw
>> <przemyslaw.kitszel@...el.com>; rdunlap@...radead.org;
>> richardcochran@...il.com; saeed@...nel.org; tariqt@...dia.com;
>> vadim.fedorenko@...ux.dev; vladimir.oltean@....com; Drewek, Wojciech
>> <wojciech.drewek@...el.com>
>> Subject: Re: [PATCH RFC v2 1/6] ethtool: add interface to read Tx hardware
>> timestamping statistics
>> 
>> On Wed, 13 Mar 2024 17:50:39 -0700 Rahul Rameshbabu wrote:
>> > > Should we give some guidance to drivers which "ignore" time stamping
>> > > requests if they used up all the "slots"? Even if just temporary until
>> > > they are fixed? Maybe we can add after all the fields something like:
>> > >
>> > >   For drivers which ignore further timestamping requests when there are
>> > >   too many in flight, the ignored requests are currently not counted by
>> > >   any of the statistics.
>> >
>> > I was actually thinking it would be better to merge them into the error
>> > counter temporarily. Reason being is that in the case Intel notices that
>> > their slots are full, they just drop traffic from my understanding
>> > today. If the error counters increment in that situation, it helps with
>> > the debug to a degree. EBUSY is an error in general.
>> 
>> That works, too, let's recommend it (FWIW no preference whether
>> in the entry for @err or somewhere separately in the kdoc).
>
> We don't drop traffic, we send the packets just fine.. We just never report a
> timestamp for them, since we don't program the hardware to capture that
> timestamp.

My actual kdoc comments are better now, but I should have been better
with the language I used here in the email. In my head, I was thinking
more about the case of not submitting HW timestamp information when
sending out the packet rather than dropping the packet entirely (I would
say that is still a timestamping error case).

--
Thanks,

Rahul Rameshbabu