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sched/clock: Fix broken stable to unstable transfer

Browse source 
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: Pavel Tatashin <pasha.tatashin@oracle.com>
Signed-off-by: Peter 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: 5680d8094f ("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: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Pavel Tatashin 2017-03-22 16:24:17 -04:00 committed by Ingo Molnar
parent 698eff6355
commit 7b09cc5a9d
1 changed files with 5 additions and 4 deletions
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9
kernel/sched/clock.c
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@ -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);