Messages in this thread Patch in this message | | | From | "Mirea, Bogdan-Stefan" <> | Subject | RE: [PATCH v3] Added "Preserve Boot Time Support" | Date | Tue, 23 May 2017 15:50:05 +0000 |
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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.
A way of setting the CLOCK_BOOTTIME is through the timekeeping_inject_sleeptime64(delta) hook, but the problem that arise here is that this hook is intended to be used on rtc_resume() code. Adding delta to CLOCK_BOOTTIME this way, the CONFIG_BOOT_TIME_PRESERVE will depend on PM_SLEEP && RTC_HCTOSYS.
The changes will be the following: diff --git a/kernel/time/sched_clock.c b/kernel/time/sched_clock.c index a26036d..6c8ad44 100644 --- a/kernel/time/sched_clock.c +++ b/kernel/time/sched_clock.c @@ -193,6 +193,26 @@ sched_clock_register(u64 (*read)(void), int bits, unsigned long rate) /* Update epoch for new counter and update 'epoch_ns' from old counter*/ new_epoch = read(); cyc = cd.actual_read_sched_clock(); + +#ifdef CONFIG_BOOT_TIME_PRESERVE + +#ifndef BOOT_TIME_PRESERVE_CMDLINE + #define BOOT_TIME_PRESERVE_CMDLINE "preserve_boot_time" +#endif + if (strstr(boot_command_line, BOOT_TIME_PRESERVE_CMDLINE)) { + static struct timespec64 delta_ts; + cyc = new_epoch; + rd.sched_clock_mask = new_mask; + rd.mult = new_mult; + rd.shift = new_shift; + + timespec64_add_ns(&delta_ts, clocksource_cyc2ns(cyc, rd.mult, rd.shift)); + timekeeping_inject_sleeptime64(&delta_ts); + + } +#endif /* CONFIG_BOOT_TIME_PRESERVE */ + ns = rd.epoch_ns + cyc_to_ns((cyc - rd.epoch_cyc) & rd.sched_clock_mask, rd.mult, rd.shift); cd.actual_read_sched_clock = read;
diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig index 4008d9f..2e392aa 100644 --- a/kernel/time/Kconfig +++ b/kernel/time/Kconfig @@ -193,5 +193,18 @@ config HIGH_RES_TIMERS hardware is not capable then this option only increases the size of the kernel image. +config BOOT_TIME_PRESERVE + bool "Preserve Boot Time Support" + default n + depends on PM_SLEEP && RTC_HCTOSYS + help + This option enables Boot Time Preservation between Bootloader and + Linux Kernel. It is based on the idea that the Bootloader (or any + other early firmware) will start the HW Timer and Linux Kernel will + count the time starting with the cycles elapsed since timer start. + + The "preserve_boot_time" parameter should be appended to kernel cmdline + from bootloader for kernel acknowledgment that the timer is running in + bootloader. endmenu endif Waiting for feedback.
Thanks, Bogdan
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