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

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Date:   Wed, 19 Oct 2022 14:23:09 +0000
From:   "Zulkifli, Muhammad Husaini" <muhammad.husaini.zulkifli@...el.com>
To:     Gal Pressman <gal@...dia.com>,
        "intel-wired-lan@...osl.org" <intel-wired-lan@...osl.org>
CC:     "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>,
        "richardcochran@...il.com" <richardcochran@...il.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 Gal,

> -----Original Message-----
> From: Gal Pressman <gal@...dia.com>
> Sent: Tuesday, 18 October, 2022 10:23 PM
> To: Zulkifli, Muhammad Husaini <muhammad.husaini.zulkifli@...el.com>;
> intel-wired-lan@...osl.org
> Cc: netdev@...r.kernel.org; kuba@...nel.org; davem@...emloft.net;
> edumazet@...gle.com; Gunasekaran, Aravindhan
> <aravindhan.gunasekaran@...el.com>; richardcochran@...il.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
> 
> Hello Muhammad,
> 
> On 18/10/2022 04:07, Muhammad Husaini Zulkifli wrote:
> > The problem is that, when there is a lot of traffic, there is a high
> > chance that the timestamps for a PTP packet will be lost if both PTP
> > and Non-PTP packets use the same SOF TIMESTAMPING TX HARDWARE
> causing the tx timeout.
> 
> Why would the timestamp be affected by the amount of traffic?
> What tx timeout?

Basically, the original timestamp register collect the timestamp at the PHY level 
and interrupt is triggered for the driver to read it. We observed timestamp missed 
issues when the traffic is high. DMA Timestamp guarantees the timestamp for every
packets as it is delivered through descriptor write-back mechanism.

When there is a timestamp missed, ptp4l application will complain there is a tx_timeout.

> 
> > DMA timestamps through socket options are not currently available to
> > the user. Because if the user wants to, they can configure the
> > hwtstamp config option to use the new introduced DMA Time Stamp flag
> > through the setsockopt().
> >
> > 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.
> 
> Is it per socket?

Yes it is per socket.

> Will there be a way to know which types of timestamps are going to be used
> on queues setup time?

We can get the which timestamp that is supported through "ethtool -T" command.
May I know why you want to know which timestamp need to configure during queue setup?

> 
> > This patch series also add a new HWTSTAMP_FILTER_DMA_TIMESTAMP
> receive
> > filters. This filter can be configured for devices that support/allow
> > the DMA timestamp retrieval on receive side.
> 
> So if I understand correctly, to solve the problem you described at the
> beginning, you'll disable port timestamp for all incoming packets? ptp
> included?

For ptp, it will always use Port Timestamp.
Other application that want to use DMA Timestamp can request for the same.