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Commit 868a3e91 authored by Thomas Gleixner's avatar Thomas Gleixner
Browse files

hrtimer: Make offset update smarter 



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: default avatarThomas Gleixner <tglx@linutronix.de>
Reviewed-by: default avatarPreeti U Murthy <preeti@linux.vnet.ibm.com>
Acked-by: default avatarPeter Zijlstra <peterz@infradead.org>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: John Stultz <john.stultz@linaro.org>
Link: http://lkml.kernel.org/r/20150414203501.132820245@linutronix.de


Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: John Stultz <john.stultz@linaro.org>
parent 21d6d52a

include/linux/hrtimer.h

+2 −2
Original line number Diff line number Diff line
@@ -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;

include/linux/timekeeper_internal.h

+2 −0
Original line number Diff line number Diff line
@@ -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 */

kernel/time/hrtimer.c

+2 −1
Original line number Diff line number Diff line
@@ -451,7 +451,8 @@ static inline ktime_t hrtimer_update_base(struct hrtimer_cpu_base *base) 
	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 */

kernel/time/timekeeping.c

+16 −7
Original line number Diff line number Diff line
@@ -602,6 +602,9 @@ static void timekeeping_update(struct timekeeper *tk, unsigned int action) 


	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(ktime_t *offs_real, ktime_t *offs_boot, 


		base = tk->tkr_mono.base;

		nsecs = timekeeping_get_ns(&tk->tkr_mono);



		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);

kernel/time/timekeeping.h

+4 −3
Original line number Diff line number Diff line
@@ -3,7 +3,8 @@ 
/*

 * Internal interfaces for kernel/time/

 */

extern ktime_t ktime_get_update_offsets_now(ktime_t *offs_real,

extern ktime_t ktime_get_update_offsets_now(unsigned int *cwsseq,

					    ktime_t *offs_real,

					    ktime_t *offs_boot,

					    ktime_t *offs_tai);