On every tick/hrtimer interrupt we update the offset variables of the clock bases. That's silly because these offsets change very seldom. Add a sequence counter to the time keeping code which keeps track of the offset updates (clock_was_set()). Have a sequence cache in the hrtimer cpu bases to evaluate whether the offsets must be updated or not. This allows us later to avoid pointless cacheline pollution. Signed-off-by: Thomas Gleixner Cc: John Stultz --- include/linux/hrtimer.h | 4 ++-- include/linux/timekeeper_internal.h | 2 ++ kernel/time/hrtimer.c | 3 ++- kernel/time/timekeeping.c | 23 ++++++++++++++++------- kernel/time/timekeeping.h | 7 ++++--- 5 files changed, 26 insertions(+), 13 deletions(-) Index: tip/include/linux/hrtimer.h =================================================================== --- tip.orig/include/linux/hrtimer.h +++ tip/include/linux/hrtimer.h @@ -163,7 +163,7 @@ enum hrtimer_base_type { * and timers * @cpu: cpu number * @active_bases: Bitfield to mark bases with active timers - * @clock_was_set: Indicates that clock was set from irq context. + * @clock_was_set_seq: Sequence counter of clock was set events * @expires_next: absolute time of the next event which was scheduled * via clock_set_next_event() * @in_hrtirq: hrtimer_interrupt() is currently executing @@ -179,7 +179,7 @@ struct hrtimer_cpu_base { raw_spinlock_t lock; unsigned int cpu; unsigned int active_bases; - unsigned int clock_was_set; + unsigned int clock_was_set_seq; #ifdef CONFIG_HIGH_RES_TIMERS ktime_t expires_next; int in_hrtirq; Index: tip/include/linux/timekeeper_internal.h =================================================================== --- tip.orig/include/linux/timekeeper_internal.h +++ tip/include/linux/timekeeper_internal.h @@ -49,6 +49,7 @@ struct tk_read_base { * @offs_boot: Offset clock monotonic -> clock boottime * @offs_tai: Offset clock monotonic -> clock tai * @tai_offset: The current UTC to TAI offset in seconds + * @clock_was_set_seq: The sequence number of clock was set events * @raw_time: Monotonic raw base time in timespec64 format * @cycle_interval: Number of clock cycles in one NTP interval * @xtime_interval: Number of clock shifted nano seconds in one NTP @@ -85,6 +86,7 @@ struct timekeeper { ktime_t offs_boot; ktime_t offs_tai; s32 tai_offset; + unsigned int clock_was_set_seq; struct timespec64 raw_time; /* The following members are for timekeeping internal use */ Index: tip/kernel/time/hrtimer.c =================================================================== --- tip.orig/kernel/time/hrtimer.c +++ tip/kernel/time/hrtimer.c @@ -451,7 +451,8 @@ static inline ktime_t hrtimer_update_bas ktime_t *offs_boot = &base->clock_base[HRTIMER_BASE_BOOTTIME].offset; ktime_t *offs_tai = &base->clock_base[HRTIMER_BASE_TAI].offset; - return ktime_get_update_offsets_now(offs_real, offs_boot, offs_tai); + return ktime_get_update_offsets_now(&base->clock_was_set_seq, + offs_real, offs_boot, offs_tai); } /* High resolution timer related functions */ Index: tip/kernel/time/timekeeping.c =================================================================== --- tip.orig/kernel/time/timekeeping.c +++ tip/kernel/time/timekeeping.c @@ -602,6 +602,9 @@ static void timekeeping_update(struct ti update_fast_timekeeper(&tk->tkr_mono, &tk_fast_mono); update_fast_timekeeper(&tk->tkr_raw, &tk_fast_raw); + + if (action & TK_CLOCK_WAS_SET) + tk->clock_was_set_seq++; } /** @@ -1927,15 +1930,19 @@ void do_timer(unsigned long ticks) /** * ktime_get_update_offsets_now - hrtimer helper + * @cwsseq: pointer to check and store the clock was set sequence number * @offs_real: pointer to storage for monotonic -> realtime offset * @offs_boot: pointer to storage for monotonic -> boottime offset * @offs_tai: pointer to storage for monotonic -> clock tai offset * - * Returns current monotonic time and updates the offsets + * Returns current monotonic time and updates the offsets if the + * sequence number in @cwsseq and timekeeper.clock_was_set_seq are + * different. + * * Called from hrtimer_interrupt() or retrigger_next_event() */ -ktime_t ktime_get_update_offsets_now(ktime_t *offs_real, ktime_t *offs_boot, - ktime_t *offs_tai) +ktime_t ktime_get_update_offsets_now(unsigned int *cwsseq, ktime_t *offs_real, + ktime_t *offs_boot, ktime_t *offs_tai) { struct timekeeper *tk = &tk_core.timekeeper; unsigned int seq; @@ -1947,10 +1954,12 @@ ktime_t ktime_get_update_offsets_now(kti base = tk->tkr_mono.base; nsecs = timekeeping_get_ns(&tk->tkr_mono); - - *offs_real = tk->offs_real; - *offs_boot = tk->offs_boot; - *offs_tai = tk->offs_tai; + if (*cwsseq != tk->clock_was_set_seq) { + *cwsseq = tk->clock_was_set_seq; + *offs_real = tk->offs_real; + *offs_boot = tk->offs_boot; + *offs_tai = tk->offs_tai; + } } while (read_seqcount_retry(&tk_core.seq, seq)); return ktime_add_ns(base, nsecs); Index: tip/kernel/time/timekeeping.h =================================================================== --- tip.orig/kernel/time/timekeeping.h +++ tip/kernel/time/timekeeping.h @@ -3,9 +3,10 @@ /* * Internal interfaces for kernel/time/ */ -extern ktime_t ktime_get_update_offsets_now(ktime_t *offs_real, - ktime_t *offs_boot, - ktime_t *offs_tai); +extern ktime_t ktime_get_update_offsets_now(unsigned int *cwsseq, + ktime_t *offs_real, + ktime_t *offs_boot, + ktime_t *offs_tai); extern int timekeeping_valid_for_hres(void); extern u64 timekeeping_max_deferment(void); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/