netdev - Re: [PATCHv3 net-next 2/3] ptp: add ioctl interface for ptp

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Date: Sat, 6 Jan 2024 00:08:57 -0800
From: Mahesh Bandewar (महेश बंडेवार) <maheshb@...gle.com>
To: Richard Cochran <richardcochran@...il.com>
Cc: Netdev <netdev@...r.kernel.org>, Linux <linux-kernel@...r.kernel.org>, 
	David Miller <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, 
	Jonathan Corbet <corbet@....net>, John Stultz <jstultz@...gle.com>, Don Hatchett <hatch@...gle.com>, 
	Yuliang Li <yuliangli@...gle.com>, Mahesh Bandewar <mahesh@...dewar.net>, 
	Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCHv3 net-next 2/3] ptp: add ioctl interface for ptp_gettimex64any()

On Fri, Jan 5, 2024 at 8:55 PM Richard Cochran <richardcochran@...il.com> wrote:
>
> On Fri, Jan 05, 2024 at 09:51:40AM -0800, Mahesh Bandewar (महेश बंडेवार) wrote:
>
> > POSIX clocks are employed in this series for syscall width
> > measurement, potentially leading to misunderstandings about
> > overlapping functionality. However, their roles are distinct and serve
> > different purposes.
>
> I don't see any difference in purposes.  The multi_clock_gettime call
> is a more general solution.  Thus it will obviate the need for any new
> PTP ioctls.
>

I disagree! NICs inherently benefit from bundled PTP devices due to
their superior low-latency, low-overhead, and precise TX/RX
timestamping capabilities. For demanding systems requiring increased
capacity, multiple NICs from various vendors are often deployed.
However, disciplining these diverse PTP devices across the host
demands a flexible approach; a general purpose syscall is not an
answer. The current PHC implementation using ioctls through exported
ptp devices (/dev/ptpX) provides a solid foundation that is per device
(/per NIC).

This series is providing another piece in an existing suite of methods
used for disciplining / precision tuning (along with adjfine, adjtime,
gettime etc.) This addition is to take that precision even further.

Having a general solution for posix timers is a nice addition.
However, expecting a general purpose syscall to eliminate need for
device ioctl is an unreasonable expectation.

Thanks,
--mahesh..

> Thanks,
> Richard