netdev - Re: [PATCH v2 0/5] Add support for DMA timestamp for non-PTP packets

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Date:   Fri, 21 Oct 2022 08:16:37 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Richard Cochran <richardcochran@...il.com>
Cc:     "Zulkifli, Muhammad Husaini" <muhammad.husaini.zulkifli@...el.com>,
        "intel-wired-lan@...osl.org" <intel-wired-lan@...osl.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "Gunasekaran, Aravindhan" <aravindhan.gunasekaran@...el.com>,
        "gal@...dia.com" <gal@...dia.com>,
        "saeed@...nel.org" <saeed@...nel.org>,
        "leon@...nel.org" <leon@...nel.org>,
        "michael.chan@...adcom.com" <michael.chan@...adcom.com>,
        "andy@...yhouse.net" <andy@...yhouse.net>,
        "Gomes, Vinicius" <vinicius.gomes@...el.com>
Subject: Re: [PATCH v2 0/5] Add support for DMA timestamp for non-PTP
 packets

On Fri, 21 Oct 2022 05:48:44 -0700 Richard Cochran wrote:
> > Could you please provide additional details about this? What do you meant by 
> > offering 1 HW Timestamp with many SW timestamps?   
> 
> - Let the PTP stack use hardware time stamps.
> 
> - Let all other applications use software time stamps.

We do need HW stamps for congestion control, the Rx ring queuing 
(as well as Tx ring scheduling jitter) is very often in 10s of msec.
Comparing the SW stamp to the HW stamp is where we derive the signal
that the system is under excessive load.