[PATCH v4 03/10] timekeeper: use the extended reading function on snapshot acquiring

[Denis Plotnikov]

Make use of the extended reading function on time snapshot getting:
get raw cycles value if extended function is defined.
The raw cycles value then is used for KVM masterclock.

This is a part of the work aiming to move to a more simple scheme of
masterclock related values calculation in KVM

Signed-off-by: Denis Plotnikov <dplotni...@virtuozzo.com>
---
 include/linux/timekeeping.h |  3 +++
 kernel/time/timekeeping.c   | 13 +++++++++++--
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/include/linux/timekeeping.h b/include/linux/timekeeping.h
index 5008e3e..528d088 100644
--- a/include/linux/timekeeping.h
+++ b/include/linux/timekeeping.h
@@ -286,6 +286,8 @@ extern void ktime_get_raw_and_real_ts64(struct timespec64 
*ts_raw,
  * @boot:      Monotonic time since boot
  * @clock_was_set_seq: The sequence number of clock was set events
  * @cs_was_changed_seq:        The sequence number of clocksource change events
+ * @cycles_valid:      The flag is true when @cycles contain actual
+ *                     number of cycles instead some cycle derivative
  */
 struct system_time_snapshot {
        u64             cycles;
@@ -294,6 +296,7 @@ struct system_time_snapshot {
        ktime_t         boot;
        unsigned int    clock_was_set_seq;
        u8              cs_was_changed_seq;
+       bool            cycles_valid;
 };
 
 /*
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 66f7701..d1aa575 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -957,12 +957,22 @@ void ktime_get_snapshot(struct system_time_snapshot 
*systime_snapshot)
        u64 nsec_raw;
        u64 nsec_real;
        u64 now;
+       struct clocksource *clock;
 
        WARN_ON_ONCE(timekeeping_suspended);
 
        do {
                seq = read_seqcount_begin(&tk_core.seq);
-               now = tk_clock_read(&tk->tkr_mono);
+               clock = READ_ONCE(tk->tkr_mono.clock);
+               if (clock->read_with_stamp)
+                       systime_snapshot->cycles_valid =
+                               clock->read_with_stamp(
+                                       clock, &now, &systime_snapshot->cycles);
+               else {
+                       systime_snapshot->cycles_valid = false;
+                       now = clock->read(clock);
+                       systime_snapshot->cycles = now;
+               }
                systime_snapshot->cs_was_changed_seq = tk->cs_was_changed_seq;
                systime_snapshot->clock_was_set_seq = tk->clock_was_set_seq;
                base_real = ktime_add(tk->tkr_mono.base,
@@ -974,7 +984,6 @@ void ktime_get_snapshot(struct system_time_snapshot 
*systime_snapshot)
                nsec_raw  = timekeeping_cycles_to_ns(&tk->tkr_raw, now);
        } while (read_seqcount_retry(&tk_core.seq, seq));
 
-       systime_snapshot->cycles = now;
        systime_snapshot->real = ktime_add_ns(base_real, nsec_real);
        systime_snapshot->raw = ktime_add_ns(base_raw, nsec_raw);
        systime_snapshot->boot = ktime_add_ns(base_boot, nsec_real);
-- 
2.7.4