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

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.comSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 698eff63
...@@ -221,7 +221,7 @@ static inline u64 wrap_max(u64 x, u64 y) ...@@ -221,7 +221,7 @@ static inline u64 wrap_max(u64 x, u64 y)
*/ */
static u64 sched_clock_local(struct sched_clock_data *scd) 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; s64 delta;
again: again:
...@@ -238,9 +238,10 @@ static u64 sched_clock_local(struct sched_clock_data *scd) ...@@ -238,9 +238,10 @@ static u64 sched_clock_local(struct sched_clock_data *scd)
* scd->tick_gtod + TICK_NSEC); * scd->tick_gtod + TICK_NSEC);
*/ */
clock = scd->tick_gtod + __gtod_offset + delta; gtod = scd->tick_gtod + __gtod_offset;
min_clock = wrap_max(scd->tick_gtod, old_clock); clock = gtod + delta;
max_clock = wrap_max(old_clock, scd->tick_gtod + TICK_NSEC); min_clock = wrap_max(gtod, old_clock);
max_clock = wrap_max(old_clock, gtod + TICK_NSEC);
clock = wrap_max(clock, min_clock); clock = wrap_max(clock, min_clock);
clock = wrap_min(clock, max_clock); clock = wrap_min(clock, max_clock);
......
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment