From 9e3680b1750b9a62680b0262c9f438de98b77655 Mon Sep 17 00:00:00 2001 From: Heena Sirwani Date: Wed, 29 Oct 2014 16:01:16 +0530 Subject: timekeeping: Provide fast accessor to the seconds part of CLOCK_MONOTONIC This is the counterpart to get_seconds() based on CLOCK_MONOTONIC. The use case for this interface are kernel internal coarse grained timestamps which do neither require the nanoseconds fraction of current time nor the CLOCK_REALTIME properties. Such timestamps can currently only retrieved by calling ktime_get_ts64() and using the tv_sec field of the returned timespec64. That's inefficient as it involves the read of the clocksource, math operations and must be protected by the timekeeper sequence counter. To avoid the sequence counter protection we restrict the return value to unsigned 32bit on 32bit machines. This covers ~136 years of uptime and therefor an overflow is not expected to hit anytime soon. To avoid math in the function we calculate the current seconds portion of CLOCK_MONOTONIC when the timekeeper gets updated in tk_update_ktime_data() similar to the CLOCK_REALTIME counterpart xtime_sec. [ tglx: Massaged changelog, simplified and commented the update function, added docbook comment ] Signed-off-by: Heena Sirwani Reviewed-by: Arnd Bergman Cc: John Stultz Cc: opw-kernel@googlegroups.com Link: http://lkml.kernel.org/r/da0b63f4bdf3478909f92becb35861197da3a905.1414578445.git.heenasirwani@gmail.com Signed-off-by: Thomas Gleixner diff --git a/include/linux/timekeeper_internal.h b/include/linux/timekeeper_internal.h index 95640dc..05af9a3 100644 --- a/include/linux/timekeeper_internal.h +++ b/include/linux/timekeeper_internal.h @@ -42,6 +42,7 @@ struct tk_read_base { * struct timekeeper - Structure holding internal timekeeping values. * @tkr: The readout base structure * @xtime_sec: Current CLOCK_REALTIME time in seconds + * @ktime_sec: Current CLOCK_MONOTONIC time in seconds * @wall_to_monotonic: CLOCK_REALTIME to CLOCK_MONOTONIC offset * @offs_real: Offset clock monotonic -> clock realtime * @offs_boot: Offset clock monotonic -> clock boottime @@ -77,6 +78,7 @@ struct tk_read_base { struct timekeeper { struct tk_read_base tkr; u64 xtime_sec; + unsigned long ktime_sec; struct timespec64 wall_to_monotonic; ktime_t offs_real; ktime_t offs_boot; diff --git a/include/linux/timekeeping.h b/include/linux/timekeeping.h index 1caa6b0..115d55e 100644 --- a/include/linux/timekeeping.h +++ b/include/linux/timekeeping.h @@ -28,6 +28,7 @@ struct timespec __current_kernel_time(void); struct timespec get_monotonic_coarse(void); extern void getrawmonotonic(struct timespec *ts); extern void ktime_get_ts64(struct timespec64 *ts); +extern time64_t ktime_get_seconds(void); extern int __getnstimeofday64(struct timespec64 *tv); extern void getnstimeofday64(struct timespec64 *tv); diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index ec1791f..a693270 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -417,7 +417,8 @@ EXPORT_SYMBOL_GPL(pvclock_gtod_unregister_notifier); */ static inline void tk_update_ktime_data(struct timekeeper *tk) { - s64 nsec; + u64 seconds; + u32 nsec; /* * The xtime based monotonic readout is: @@ -426,13 +427,22 @@ static inline void tk_update_ktime_data(struct timekeeper *tk) * nsec = base_mono + now(); * ==> base_mono = (xtime_sec + wtm_sec) * 1e9 + wtm_nsec */ - nsec = (s64)(tk->xtime_sec + tk->wall_to_monotonic.tv_sec); - nsec *= NSEC_PER_SEC; - nsec += tk->wall_to_monotonic.tv_nsec; - tk->tkr.base_mono = ns_to_ktime(nsec); + seconds = (u64)(tk->xtime_sec + tk->wall_to_monotonic.tv_sec); + nsec = (u32) tk->wall_to_monotonic.tv_nsec; + tk->tkr.base_mono = ns_to_ktime(seconds * NSEC_PER_SEC + nsec); /* Update the monotonic raw base */ tk->base_raw = timespec64_to_ktime(tk->raw_time); + + /* + * The sum of the nanoseconds portions of xtime and + * wall_to_monotonic can be greater/equal one second. Take + * this into account before updating tk->ktime_sec. + */ + nsec += (u32)(tk->tkr.xtime_nsec >> tk->tkr.shift); + if (nsec >= NSEC_PER_SEC) + seconds++; + tk->ktime_sec = seconds; } /* must hold timekeeper_lock */ @@ -648,6 +658,24 @@ void ktime_get_ts64(struct timespec64 *ts) } EXPORT_SYMBOL_GPL(ktime_get_ts64); +/** + * ktime_get_seconds - Get the seconds portion of CLOCK_MONOTONIC + * + * Returns the seconds portion of CLOCK_MONOTONIC with a single non + * serialized read. tk->ktime_sec is of type 'unsigned long' so this + * works on both 32 and 64 bit systems. On 32 bit systems the readout + * covers ~136 years of uptime which should be enough to prevent + * premature wrap arounds. + */ +time64_t ktime_get_seconds(void) +{ + struct timekeeper *tk = &tk_core.timekeeper; + + WARN_ON(timekeeping_suspended); + return tk->ktime_sec; +} +EXPORT_SYMBOL_GPL(ktime_get_seconds); + #ifdef CONFIG_NTP_PPS /** -- cgit v0.10.2 From dbe7aa622db96b5cd601f59d09c4f00b98b76079 Mon Sep 17 00:00:00 2001 From: Heena Sirwani Date: Wed, 29 Oct 2014 16:01:50 +0530 Subject: timekeeping: Provide y2038 safe accessor to the seconds portion of CLOCK_REALTIME ktime_get_real_seconds() is the replacement function for get_seconds() returning the seconds portion of CLOCK_REALTIME in a time64_t. For 64bit the function is equivivalent to get_seconds(), but for 32bit it protects the readout with the timekeeper sequence count. This is required because 32-bit machines cannot access 64-bit tk->xtime_sec variable atomically. [tglx: Massaged changelog and added docbook comment ] Signed-off-by: Heena Sirwani Reviewed-by: Arnd Bergman Cc: John Stultz Cc: opw-kernel@googlegroups.com Link: http://lkml.kernel.org/r/7adcfaa8962b8ad58785d9a2456c3f77d93c0ffb.1414578445.git.heenasirwani@gmail.com Signed-off-by: Thomas Gleixner diff --git a/include/linux/timekeeping.h b/include/linux/timekeeping.h index 115d55e..91454de 100644 --- a/include/linux/timekeeping.h +++ b/include/linux/timekeeping.h @@ -29,6 +29,7 @@ struct timespec get_monotonic_coarse(void); extern void getrawmonotonic(struct timespec *ts); extern void ktime_get_ts64(struct timespec64 *ts); extern time64_t ktime_get_seconds(void); +extern time64_t ktime_get_real_seconds(void); extern int __getnstimeofday64(struct timespec64 *tv); extern void getnstimeofday64(struct timespec64 *tv); diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index a693270..0aef92a 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -676,6 +676,36 @@ time64_t ktime_get_seconds(void) } EXPORT_SYMBOL_GPL(ktime_get_seconds); +/** + * ktime_get_real_seconds - Get the seconds portion of CLOCK_REALTIME + * + * Returns the wall clock seconds since 1970. This replaces the + * get_seconds() interface which is not y2038 safe on 32bit systems. + * + * For 64bit systems the fast access to tk->xtime_sec is preserved. On + * 32bit systems the access must be protected with the sequence + * counter to provide "atomic" access to the 64bit tk->xtime_sec + * value. + */ +time64_t ktime_get_real_seconds(void) +{ + struct timekeeper *tk = &tk_core.timekeeper; + time64_t seconds; + unsigned int seq; + + if (IS_ENABLED(CONFIG_64BIT)) + return tk->xtime_sec; + + do { + seq = read_seqcount_begin(&tk_core.seq); + seconds = tk->xtime_sec; + + } while (read_seqcount_retry(&tk_core.seq, seq)); + + return seconds; +} +EXPORT_SYMBOL_GPL(ktime_get_real_seconds); + #ifdef CONFIG_NTP_PPS /** -- cgit v0.10.2