[PATCH v14 17/25] time: default boot time offset to local_clock()

Pavel Tatashin
2018-07-18T02:22:03Z

read_persistent_wall_and_boot_offset() is called during boot to read
both the persistent clock and also return the offset between the boot time
and the value of persistent clock.

Change the default boot_offset from zero to local_clock() so architectures,
that do not have a dedicated boot_clock but have early sched_clock(), such
as SPARCv9, x86, and possibly more will benefit from this change by getting
a better and more consistent estimate of the boot time without need for an
arch specific implementation.

Signed-off-by: Pavel Tatashin <pasha.tatashin@oracle.com>
---
kernel/time/timekeeping.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index cb738f825c12..30d7f64ffc87 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -1503,14 +1503,17 @@ void __weak read_persistent_clock64(struct timespec64 *ts64)
* Weak dummy function for arches that do not yet support it.
* wall_time - current time as returned by persistent clock
* boot_offset - offset that is defined as wall_time - boot_time
- * default to 0.
+ * The default function calculates offset based on the current value of
+ * local_clock(). This way architectures that support sched_clock() but don't
+ * support dedicated boot time clock will provide the best estimate of the
+ * boot time.
*/
void __weak __init
read_persistent_wall_and_boot_offset(struct timespec64 *wall_time,
struct timespec64 *boot_offset)
{
read_persistent_clock64(wall_time);
- *boot_offset = (struct timespec64){0};
+ *boot_offset = ns_to_timespec64(local_clock());
}

/* Flag for if timekeeping_resume() has injected sleeptime */
--
2.18.0