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@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>
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 @@
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 @@
/**
* 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 @@
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);