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

Denis Plotnikov
2017-08-02T14:39:32Z

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 <dplotnikov@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