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 17:50:10 +0000
From: "Keller, Jacob E" <jacob.e.keller@...el.com>
To: Jakub Kicinski <kuba@...nel.org>, Rahul Rameshbabu
	<rrameshbabu@...dia.com>
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Subject: RE: [PATCH RFC v2 1/6] ethtool: add interface to read Tx hardware
 timestamping statistics



> -----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.