linux-kernel - Re: [patch 00/26] timekeeping: Provide support for independent PTP timekeepers

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <aCRCe8STiX03WcxU@localhost>
Date: Wed, 14 May 2025 09:12:59 +0200
From: Miroslav Lichvar <mlichvar@...hat.com>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: LKML <linux-kernel@...r.kernel.org>, netdev@...r.kernel.org,
	Richard Cochran <richardcochran@...il.com>,
	Christopher Hall <christopher.s.hall@...el.com>,
	David Zage <david.zage@...el.com>, John Stultz <jstultz@...gle.com>,
	Frederic Weisbecker <frederic@...nel.org>,
	Anna-Maria Behnsen <anna-maria@...utronix.de>,
	Werner Abt <werner.abt@...nberg-usa.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Stephen Boyd <sboyd@...nel.org>,
	Thomas Weißschuh <thomas.weissschuh@...utronix.de>,
	Kurt Kanzenbach <kurt@...utronix.de>,
	Nam Cao <namcao@...utronix.de>,
	Alex Gieringer <gieri@...utronix.de>
Subject: Re: [patch 00/26] timekeeping: Provide support for independent PTP
 timekeepers

On Tue, May 13, 2025 at 05:12:54PM +0200, Thomas Gleixner wrote:
> This series addresses the timekeeping part by utilizing the existing
> timekeeping and NTP infrastructure, which has been prepared for
> multi-instance in recent kernels.

This looks very interesting. I ran some quick tests and it seems to
work as expected from the user space point of view. I can enable the
clock and synchronize it to a PTP HW clock or the system REALTIME
clock. ADJ_TICK works too.

To get accuracy and stability comparable to CLOCK_REALTIME, there will
need to be some support for cross timestamping against CLOCK_REALTIME
and/or PTP HW clocks, e.g. a variant of the PTP_SYS_OFFSET_PRECISE and
PTP_SYS_OFFSET_EXTENDED ioctls where the target clock can be selected.

The "PTP" naming of these new clocks doesn't seem right to me though
and I suspect it would just create more confusion. I don't see
anything specific to PTP here. There is no timestamping of network
packets, no /dev/ptp device, no PTP ioctls. To me they look like
secondary or auxiliary system realtime clocks. I propose to rename
them from CLOCK_PTP0-7 to CLOCK_REALTIME2-9, CLOCK_AUXILIARY0-7, or
CLOCK_AUX0-7.

-- 
Miroslav Lichvar