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

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Date: Sun, 7 Jan 2024 13:13:42 -0800
From: Richard Cochran <richardcochran@...il.com>
To: Mahesh Bandewar (महेश बंडेवार) <maheshb@...gle.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 Sat, Jan 06, 2024 at 12:08:57AM -0800, Mahesh Bandewar (महेश बंडेवार) wrote:
> 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.

This reads like marketing fluff.

You fail to provide any *technical* reason why your proposed cross
time stamp method can only work with a new ioctl, and not as the back
end of a system call.

Thanks,
Richard