Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 7b09cc5a authored by Pavel Tatashin's avatar Pavel Tatashin Committed by Ingo Molnar
Browse files

sched/clock: Fix broken stable to unstable transfer 



When it is determined that the clock is actually unstable, and
we switch from stable to unstable, the __clear_sched_clock_stable()
function is eventually called.

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.

This can result in tick granularity sched_clock() values, so fix it.

Signed-off-by: default avatarPavel Tatashin <pasha.tatashin@oracle.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: hpa@zytor.com
Fixes: 5680d809 ("sched/clock: Provide better clock continuity")
Link: http://lkml.kernel.org/r/1490214265-899964-2-git-send-email-pasha.tatashin@oracle.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 698eff63

kernel/sched/clock.c

+5 −4
Original line number Diff line number Diff line
@@ -221,7 +221,7 @@ 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:
@@ -238,9 +238,10 @@ 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);