netdev - Re: igc: missing HW timestamps at TX

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Message-ID: <d5571f0ea205e26bced51220044781131296aaac.camel@ericsson.com>
Date:   Thu, 11 Aug 2022 08:54:20 +0000
From:   Ferenc Fejes <ferenc.fejes@...csson.com>
To:     "vinicius.gomes@...el.com" <vinicius.gomes@...el.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     "marton12050@...il.com" <marton12050@...il.com>,
        "peti.antal99@...il.com" <peti.antal99@...il.com>
Subject: Re: igc: missing HW timestamps at TX

Hi Vinicius!

On Tue, 2022-07-19 at 09:40 +0200, Fejes Ferenc wrote:
> Hi Vinicius!
> 
> On Mon, 2022-07-18 at 11:46 -0300, Vinicius Costa Gomes wrote:
> > Hi Ferenc,
> > 
> > Ferenc Fejes <ferenc.fejes@...csson.com> writes:
> > 
> > > (Ctrl+Enter'd by mistake)
> > > 
> > > My question here: is there anything I can quickly try to avoid
> > > that
> > > behavior? Even when I send only a few (like 10) packets but on
> > > fast
> > > rate (5us between packets) I get missing TX HW timestamps. The
> > > receive
> > > side looks much more roboust, I cannot noticed missing HW
> > > timestamps
> > > there.
> > 
> > There's a limitation in the i225/i226 in the number of "in flight"
> > TX
> > timestamps they are able to handle. The hardware has 4 sets of
> > registers
> > to handle timestamps.
> > 
> > There's an aditional issue that the driver as it is right now, only
> > uses
> > one set of those registers.
> > 
> > I have one only briefly tested series that enables the driver to
> > use
> > the
> > full set of TX timestamp registers. Another reason that it was not
> > proposed yet is that I still have to benchmark it and see what is
> > the
> > performance impact.
> 
> Thank you for the quick reply! I'm glad you already have this series
> right off the bat. I'll be back when we done with a quick testing,
> hopefully sooner than later.

Sorry for the late reply. I had time for a few tests, with the patch.
For my tests it looks much better. I send a packet in every 500us with
isochron-send, TX SW and HW timestamping enabled and for 10000 packets
I see zero lost timestamp. Even for 100000 packets only a few dropped
HW timestamps visible.

With iperf TCP test line-rate achiveable just like without the patch.

> > 
> > If you are feeling adventurous and feel like helping test it, here
> > is
> > the link:
> > 
> > https%3A%2F%2Fgithub.com%2Fvcgomes%2Fnet-next%2Ftree%2Figc-
> > multiple-tstamp-timers-lock-new
> > 

Is there any test in partucular you interested in? My testbed is
configured so I can do some.

> > 
> > Cheers,
> 
> Best,
> Ferenc

Best,
Ferenc