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

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Date:   Tue, 18 Oct 2022 14:12:37 +0000
From:   "Zulkifli, Muhammad Husaini" <muhammad.husaini.zulkifli@...el.com>
To:     Richard Cochran <richardcochran@...il.com>
CC:     "intel-wired-lan@...osl.org" <intel-wired-lan@...osl.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "kuba@...nel.org" <kuba@...nel.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

Hi Richard,

Thanks for your review. Replied inline.

> -----Original Message-----
> From: Richard Cochran <richardcochran@...il.com>
> Sent: Tuesday, 18 October, 2022 7:45 PM
> To: Zulkifli, Muhammad Husaini <muhammad.husaini.zulkifli@...el.com>
> Cc: intel-wired-lan@...osl.org; netdev@...r.kernel.org; kuba@...nel.org;
> davem@...emloft.net; edumazet@...gle.com; Gunasekaran, Aravindhan
> <aravindhan.gunasekaran@...el.com>; gal@...dia.com; saeed@...nel.org;
> leon@...nel.org; michael.chan@...adcom.com; 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 Tue, Oct 18, 2022 at 09:07:28AM +0800, Muhammad Husaini Zulkifli
> wrote:
> 
> > With these additional socket options, users can continue to utilise HW
> > timestamps for PTP while specifying non-PTP packets to use DMA
> > timestamps if the NIC can support them.
> 
> What is the use case for reporting DMA transmit time?
> 
> How is this better than using SOF_TIMESTAMPING_TX_SOFTWARE ?

The ideal situation is to use SOF TIMESTAMPING TX SOFTWARE. 
Application side will undoubtedly want to utilize PHY timestamps as much as possible. 

But if every application requested the HW Tx timestamp, especially during periods of high load like TSN, 
in some cases when the controller only supports 1 HW timestamp, it would be a disaster.
We will observe some missing timestamp reported later.

Using the DMA transmit time for the tx timestamp, if supported, is one of the solutions that we propose here.

> 
> 
> Thanks,
> Richard