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hrtimer: Make offset update smarter

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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 <tglx@linutronix.de>
Reviewed-by: Preeti U Murthy <preeti@linux.vnet.ibm.com>
Acked-by: Peter 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: Thomas Gleixner <tglx@linutronix.de>
Cc: John Stultz <john.stultz@linaro.org>
This commit is contained in:
Thomas Gleixner 2015-04-14 21:08:37 +00:00
parent 21d6d52a1b
commit 868a3e915f
5 changed files with 26 additions and 13 deletions
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4
include/linux/hrtimer.h
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@ -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;

2
include/linux/timekeeper_internal.h
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@ -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 */

3
kernel/time/hrtimer.c
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@ -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 */

23
kernel/time/timekeeping.c
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@ -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);
*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);

7
kernel/time/timekeeping.h
View File

@ -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);