On Tuesday, May 23, 2017 7:39 PM, Thomas Gleixner wrote: > On Tue, 23 May 2017, Mirea, Bogdan-Stefan wrote: > > On Monday, May 22, 2017 12:36 AM, Thomas Gleixner wrote: > > > On Fri, 19 May 2017, Bogdan Mirea wrote: > > > This adds a arch_timer specific command line option. Why is this > > > arch_timer > > > specific? So if any other platform wants to gain this feature then we > > > end > > > up copying that mess to every single timer implementation? Certainly > > > NOT! > > > Exactly nothing. settimeofday() modifies CLOCK_REALTIME and if the > > > platform > > > has an early accessible RTC, you hereby wreckaged wall_time. If the > > > RTC > > > readout comes later then CLOCK_REALTIME is overwritten. So what is > > > this > > > supposed to do? > > > > > > It has absolutely nothing to do with CLOCK_BOOTTIME. /proc/uptime is > > > based > > > on CLOCK_BOOTTIME, which is the CLOCK_MONOTONIC time since system > > > boot. The > > > difference between CLOCK_MONOTONIC and CLOCK_BOOTTIME is that > > > CLOCK_MONOTONIC does not advance during suspend, but > CLOCK_BOOTTIME > > > takes > > > the suspended time into account. > > Thanks for feedback. > > The idea of this patch was of a POC and this is why the code was > > isolated in timer driver, which I agree is not a good idea for other > > platforms to copy this since we can simply do all the things in > > sched_clock_register() function guarded with > CONFIG_BOOT_TIME_PRESERVE. > > The patch was created for an internal project where no RTC was available > > and no user-space apps were making any settimeofday(), and the use of > > do_settimeofday() seemed safe. But yes, considering that the > > CLOCK_REALTIME can be easily changed it should not be used here. > > It does not matter at all whether you have a RTC or settimeofday() is used > or not. > > Again: > > > > It has absolutely nothing to do with CLOCK_BOOTTIME. /proc/uptime is > > > based on CLOCK_BOOTTIME, which is the CLOCK_MONOTONIC time since > system > > > boot. The difference between CLOCK_MONOTONIC and CLOCK_BOOTTIME > is that > > > CLOCK_MONOTONIC does not advance during suspend, but > CLOCK_BOOTTIME > > > takes the suspended time into account. > > So using settimeofday() for any of what you want to do is bogus and > useless.
Got it. Thanks! I am thinking about using timekeeping_inject_sleeptime64(delta) hook to add a delta time at boot to the CLOCK_BOOTTIME, but the problem that arise here is that this hook is intended to be used on rtc_resume() code (to add the time spent in suspend to CLOCK_BOOTTIME). >From my point of view this will do the trick even if the CONFIG_BOOT_TIME_PRESERVE will then depend on PM_SLEEP && RTC_HCTOSYS (needed by timekeeping_inject_sleeptime64 to work). Do you think this is a good approach? Regards, Bogdan