[tip:timers/core] hrtimer: Make offset update smarter

From: tip-bot for Thomas Gleixner
Date: Wed Apr 22 2015 - 15:07:35 EST

Commit-ID: 868a3e915f7f5eba8f8cb4f7da2276760807c51c
Gitweb: http://git.kernel.org/tip/868a3e915f7f5eba8f8cb4f7da2276760807c51c
Author: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
AuthorDate: Tue, 14 Apr 2015 21:08:37 +0000
Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Wed, 22 Apr 2015 17:06:49 +0200

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: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Reviewed-by: Preeti U Murthy <preeti@xxxxxxxxxxxxxxxxxx>
Acked-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
Cc: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: John Stultz <john.stultz@xxxxxxxxxx>
Link: http://lkml.kernel.org/r/20150414203501.132820245@xxxxxxxxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: John Stultz <john.stultz@xxxxxxxxxx>
---
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(-)

diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
index e292830..5e04f8f 100644
--- a/include/linux/hrtimer.h
+++ b/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;
diff --git a/include/linux/timekeeper_internal.h b/include/linux/timekeeper_internal.h
index fb86963..6f8276a 100644
--- a/include/linux/timekeeper_internal.h
+++ b/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 */
diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 9e111dd..8ce9b31 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -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 */
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index dd1efa6..3365e32 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -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);
diff --git a/kernel/time/timekeeping.h b/kernel/time/timekeeping.h
index 4d177fc..704f595 100644
--- a/kernel/time/timekeeping.h
+++ b/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@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/