lkml.org 
[lkml]   [2018]   [Jul]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[tip:x86/timers] timekeeping: Default boot time offset to local_clock()
Commit-ID:  4b1b7f8054896cee25669f6cea7cb6dd17f508f7
Gitweb: https://git.kernel.org/tip/4b1b7f8054896cee25669f6cea7cb6dd17f508f7
Author: Pavel Tatashin <pasha.tatashin@oracle.com>
AuthorDate: Thu, 19 Jul 2018 16:55:35 -0400
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitDate: Fri, 20 Jul 2018 00:02:41 +0200

timekeeping: Default boot time offset to local_clock()

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>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: steven.sistare@oracle.com
Cc: daniel.m.jordan@oracle.com
Cc: linux@armlinux.org.uk
Cc: schwidefsky@de.ibm.com
Cc: heiko.carstens@de.ibm.com
Cc: john.stultz@linaro.org
Cc: sboyd@codeaurora.org
Cc: hpa@zytor.com
Cc: douly.fnst@cn.fujitsu.com
Cc: peterz@infradead.org
Cc: prarit@redhat.com
Cc: feng.tang@intel.com
Cc: pmladek@suse.com
Cc: gnomes@lxorguk.ukuu.org.uk
Cc: linux-s390@vger.kernel.org
Cc: boris.ostrovsky@oracle.com
Cc: jgross@suse.com
Cc: pbonzini@redhat.com
Link: https://lkml.kernel.org/r/20180719205545.16512-17-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 */
\
 
 \ /
  Last update: 2018-07-20 00:30    [W:0.326 / U:0.640 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site