Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1606980

[v1 1/9] sched/clock: broken stable to unstable transfer

Show all headers | View raw

When it is determined that clock is actually unstable, and we switch from
stable to unstable the following function is eventually called:

__clear_sched_clock_stable()

In this function we set gtod_offset so the following holds true:

sched_clock() + raw_offset == ktime_get_ns() + gtod_offset

But instead of getting the latest timestamps, we use the last values
from scd, so instead of sched_clock() we use scd->tick_raw, and instead of
ktime_get_ns() we use scd->tick_gtod.

However, later, when we use gtod_offset sched_clock_local() we do not add
it to scd->tick_gtod to calculate the correct clock value when we determine
the boundaries for min/max clocks.

Signed-off-by: Pavel Tatashin <pasha.tatashin@oracle.com>
---
 kernel/sched/clock.c |    9 +++++----
 1 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c
index a08795e..2bc1090 100644
--- a/kernel/sched/clock.c
+++ b/kernel/sched/clock.c
@@ -214,7 +214,7 @@ static inline u64 wrap_max(u64 x, u64 y)
  */
 static u64 sched_clock_local(struct sched_clock_data *scd)
 {
-	u64 now, clock, old_clock, min_clock, max_clock;
+	u64 now, clock, old_clock, min_clock, max_clock, gtod;
 	s64 delta;
 
 again:
@@ -231,9 +231,10 @@ static u64 sched_clock_local(struct sched_clock_data *scd)
 	 *		      scd->tick_gtod + TICK_NSEC);
 	 */
 
-	clock = scd->tick_gtod + gtod_offset + delta;
-	min_clock = wrap_max(scd->tick_gtod, old_clock);
-	max_clock = wrap_max(old_clock, scd->tick_gtod + TICK_NSEC);
+	gtod = scd->tick_gtod + gtod_offset;
+	clock = gtod + delta;
+	min_clock = wrap_max(gtod, old_clock);
+	max_clock = wrap_max(old_clock, gtod + TICK_NSEC);
 
 	clock = wrap_max(clock, min_clock);
 	clock = wrap_min(clock, max_clock);
-- 
1.7.1

Back to linux.kernel | Previous | Next — Next in thread | Find similar | Unroll thread

Thread

[v1 1/9] sched/clock: broken stable to unstable transfer Pavel Tatashin <pasha.tatashin@oracle.com> - 2017-03-22 21:20 +0100
  [tip:sched/urgent] sched/clock: Fix broken stable to unstable  transfer tip-bot for Pavel Tatashin <tipbot@zytor.com> - 2017-03-27 12:40 +0200

csiph-web