From a3ed0e4393d6885b4af7ce84b437dc696490a530 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Wed, 25 Apr 2018 15:33:38 +0200 Subject: Revert: Unify CLOCK_MONOTONIC and CLOCK_BOOTTIME Revert commits 92af4dcb4e1c ("tracing: Unify the "boot" and "mono" tracing clocks") 127bfa5f4342 ("hrtimer: Unify MONOTONIC and BOOTTIME clock behavior") 7250a4047aa6 ("posix-timers: Unify MONOTONIC and BOOTTIME clock behavior") d6c7270e913d ("timekeeping: Remove boot time specific code") f2d6fdbfd238 ("Input: Evdev - unify MONOTONIC and BOOTTIME clock behavior") d6ed449afdb3 ("timekeeping: Make the MONOTONIC clock behave like the BOOTTIME clock") 72199320d49d ("timekeeping: Add the new CLOCK_MONOTONIC_ACTIVE clock") As stated in the pull request for the unification of CLOCK_MONOTONIC and CLOCK_BOOTTIME, it was clear that we might have to revert the change. As reported by several folks systemd and other applications rely on the documented behaviour of CLOCK_MONOTONIC on Linux and break with the above changes. After resume daemons time out and other timeout related issues are observed. Rafael compiled this list: * systemd kills daemons on resume, after >WatchdogSec seconds of suspending (Genki Sky). [Verified that that's because systemd uses CLOCK_MONOTONIC and expects it to not include the suspend time.] * systemd-journald misbehaves after resume: systemd-journald[7266]: File /var/log/journal/016627c3c4784cd4812d4b7e96a34226/system.journal corrupted or uncleanly shut down, renaming and replacing. (Mike Galbraith). * NetworkManager reports "networking disabled" and networking is broken after resume 50% of the time (Pavel). [May be because of systemd.] * MATE desktop dims the display and starts the screensaver right after system resume (Pavel). * Full system hang during resume (me). [May be due to systemd or NM or both.] That happens on debian and open suse systems. It's sad, that these problems were neither catched in -next nor by those folks who expressed interest in this change. Reported-by: Rafael J. Wysocki Reported-by: Genki Sky , Reported-by: Pavel Machek Signed-off-by: Thomas Gleixner Cc: Dmitry Torokhov Cc: John Stultz Cc: Jonathan Corbet Cc: Kevin Easton Cc: Linus Torvalds Cc: Mark Salyzyn Cc: Michael Kerrisk Cc: Peter Zijlstra Cc: Petr Mladek Cc: Prarit Bhargava Cc: Sergey Senozhatsky Cc: Steven Rostedt --- Documentation/trace/ftrace.rst | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) (limited to 'Documentation') diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst index e45f0786f3f9..67d9c38e95eb 100644 --- a/Documentation/trace/ftrace.rst +++ b/Documentation/trace/ftrace.rst @@ -461,9 +461,17 @@ of ftrace. Here is a list of some of the key files: and ticks at the same rate as the hardware clocksource. boot: - Same as mono. Used to be a separate clock which accounted - for the time spent in suspend while CLOCK_MONOTONIC did - not. + This is the boot clock (CLOCK_BOOTTIME) and is based on the + fast monotonic clock, but also accounts for time spent in + suspend. Since the clock access is designed for use in + tracing in the suspend path, some side effects are possible + if clock is accessed after the suspend time is accounted before + the fast mono clock is updated. In this case, the clock update + appears to happen slightly sooner than it normally would have. + Also on 32-bit systems, it's possible that the 64-bit boot offset + sees a partial update. These effects are rare and post + processing should be able to handle them. See comments in the + ktime_get_boot_fast_ns() function for more information. To set a clock, simply echo the clock name into this file:: -- cgit