From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thomas Gleixner Subject: Re: [PATCH v2 1/4] time: rtc-lib: Add rtc_show_time(const char *prefix_msg) Date: Wed, 19 Jul 2017 09:23:25 +0200 (CEST) Message-ID: References: <20170718211930.123077-1-salyzyn@android.com> <8afb372a-3951-6fb9-c0be-82756623061f@android.com> <5016ccc4-7faa-b61e-c0a1-b851620849c7@android.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Return-path: In-Reply-To: <5016ccc4-7faa-b61e-c0a1-b851620849c7@android.com> Sender: linux-kernel-owner@vger.kernel.org To: Mark Salyzyn Cc: LKML , rjw@rjwysocki.net, len.brown@intel.com, pavel@ucw.cz, linux-pm@vger.kernel.org, a.zummo@towertech.it, alexandre.belloni@free-electrons.com, linux-rtc@vger.kernel.org, andy.shevchenko@gmail.com, Mark Salyzyn , "Paul E. McKenney" , Thierry Strudel , John Stultz , Richard Cochran , Nicolas Pitre , Kees Cook , Ingo Molnar , Peter Zijlstra , Prarit Bhargava List-Id: linux-pm@vger.kernel.org On Tue, 18 Jul 2017, Mark Salyzyn wrote: > On 07/18/2017 03:35 PM, Thomas Gleixner wrote: > > There was some discussion about making the clock source for dmesg time > > stamps selectable, so you can use MONOTONIC, REALTIME, BOOTTIME. The > > patches looked sensible, but there was some showstopper vs. the user space > > dmesg utility. See: > > The timestamps are useful for the 'second' purpose of these patches when > dmesg time is BOOTTIME or MONOTONIC, and can be turned off if REALTIME > is selected. Having rtc_show_time a single point for switching this no doubt > helps, > not hinders, that dmesg issue. > > The inflection points would still serve a purpose, still need > suspend/resume/hibernate/restore. The reboot messages are _only_ useful to > us with their timestamps, as I checked and the only tools that use those are > for log synchronization. We may be able to do away with them on REALTIME > dmesg'ing; but the standardization of the message as a marker would have a > legacy purpose (!) > > NB: We have a similar configuration for the user space logger, which can be > configured to report in MONOTONIC time. We have yet to have a vendor > use the feature, opting for REALTIME logging for user space activities. > Our klogd (which runs at background priority and is batched) manages a > histogram relationship between MONOTONIC and REALTIME helped by these > prints and incorporates the REALTIME dmesg logs merged into our user > space logging database. There is another option to remedy this and the dmesg tooling issues: Instead of switching the time stamps in dmesg to a different clock we might as well have an optional secondary timestamp. So instead of: [ 341.590930] wlan0: associated you would get: [ 341.590930] [ sec.usec] wlan0: associated where the second time stamp would be CLOCK_REALTIME/BOOTTIME. That should also solve Prarits problem, hmm? Thanks, tglx