From: Pavel Tatashin <pasha.tatashin@oracle.com>
To: steven.sistare@oracle.com, daniel.m.jordan@oracle.com,
linux@armlinux.org.uk, schwidefsky@de.ibm.com,
heiko.carstens@de.ibm.com, john.stultz@linaro.org,
sboyd@codeaurora.org, x86@kernel.org,
linux-kernel@vger.kernel.org, mingo@redhat.com,
tglx@linutronix.de, hpa@zytor.com, douly.fnst@cn.fujitsu.com,
peterz@infradead.org, prarit@redhat.com, feng.tang@intel.com,
pmladek@suse.com, gnomes@lxorguk.ukuu.org.uk,
linux-s390@vger.kernel.org, pasha.tatashin@oracle.com,
boris.ostrovsky@oracle.com, jgross@suse.com
Subject: [PATCH v13 09/18] time: replace read_boot_clock64() with read_persistent_wall_and_boot_offset()
Date: Wed, 11 Jul 2018 20:04:10 -0400 [thread overview]
Message-ID: <20180712000419.5165-10-pasha.tatashin@oracle.com> (raw)
In-Reply-To: <20180712000419.5165-1-pasha.tatashin@oracle.com>
If architecture does not support exact boot time, it is challenging to
estimate boot time without having a reference to the current persistent
clock value. Yet, it cannot read the persistent clock time again, because
this may lead to math discrepancies with the caller of read_boot_clock64()
who have read the persistent clock at a different time.
This is why it is better to provide two values simultaneously: the
persistent clock value, and the boot time.
Replace read_boot_clock64() with:
read_persistent_wall_and_boot_offset(wall_time, boot_offset)
Where wall_time is returned by read_persistent_clock()
And boot_offset is wall_time - boot time, which defaults to 0.
Signed-off-by: Pavel Tatashin <pasha.tatashin@oracle.com>
---
include/linux/timekeeping.h | 3 +-
kernel/time/timekeeping.c | 59 +++++++++++++++++++------------------
2 files changed, 32 insertions(+), 30 deletions(-)
diff --git a/include/linux/timekeeping.h b/include/linux/timekeeping.h
index 86bc2026efce..686bc27acef0 100644
--- a/include/linux/timekeeping.h
+++ b/include/linux/timekeeping.h
@@ -243,7 +243,8 @@ extern void ktime_get_snapshot(struct system_time_snapshot *systime_snapshot);
extern int persistent_clock_is_local;
extern void read_persistent_clock64(struct timespec64 *ts);
-extern void read_boot_clock64(struct timespec64 *ts);
+void read_persistent_clock_and_boot_offset(struct timespec64 *wall_clock,
+ struct timespec64 *boot_offset);
extern int update_persistent_clock64(struct timespec64 now);
/*
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 4786df904c22..cb738f825c12 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -17,6 +17,7 @@
#include <linux/nmi.h>
#include <linux/sched.h>
#include <linux/sched/loadavg.h>
+#include <linux/sched/clock.h>
#include <linux/syscore_ops.h>
#include <linux/clocksource.h>
#include <linux/jiffies.h>
@@ -1496,18 +1497,20 @@ void __weak read_persistent_clock64(struct timespec64 *ts64)
}
/**
- * read_boot_clock64 - Return time of the system start.
+ * read_persistent_wall_and_boot_offset - Read persistent clock, and also offset
+ * from the boot.
*
* Weak dummy function for arches that do not yet support it.
- * Function to read the exact time the system has been started.
- * Returns a timespec64 with tv_sec=0 and tv_nsec=0 if unsupported.
- *
- * XXX - Do be sure to remove it once all arches implement it.
+ * wall_time - current time as returned by persistent clock
+ * boot_offset - offset that is defined as wall_time - boot_time
+ * default to 0.
*/
-void __weak read_boot_clock64(struct timespec64 *ts)
+void __weak __init
+read_persistent_wall_and_boot_offset(struct timespec64 *wall_time,
+ struct timespec64 *boot_offset)
{
- ts->tv_sec = 0;
- ts->tv_nsec = 0;
+ read_persistent_clock64(wall_time);
+ *boot_offset = (struct timespec64){0};
}
/* Flag for if timekeeping_resume() has injected sleeptime */
@@ -1521,28 +1524,29 @@ static bool persistent_clock_exists;
*/
void __init timekeeping_init(void)
{
+ struct timespec64 wall_time, boot_offset, wall_to_mono;
struct timekeeper *tk = &tk_core.timekeeper;
struct clocksource *clock;
unsigned long flags;
- struct timespec64 now, boot, tmp;
-
- read_persistent_clock64(&now);
- if (!timespec64_valid_strict(&now)) {
- pr_warn("WARNING: Persistent clock returned invalid value!\n"
- " Check your CMOS/BIOS settings.\n");
- now.tv_sec = 0;
- now.tv_nsec = 0;
- } else if (now.tv_sec || now.tv_nsec)
- persistent_clock_exists = true;
- read_boot_clock64(&boot);
- if (!timespec64_valid_strict(&boot)) {
- pr_warn("WARNING: Boot clock returned invalid value!\n"
- " Check your CMOS/BIOS settings.\n");
- boot.tv_sec = 0;
- boot.tv_nsec = 0;
+ read_persistent_wall_and_boot_offset(&wall_time, &boot_offset);
+ if (timespec64_valid_strict(&wall_time) &&
+ timespec64_to_ns(&wall_time) > 0) {
+ persistent_clock_exists = true;
+ } else {
+ pr_warn("Persistent clock returned invalid value");
+ wall_time = (struct timespec64){0};
}
+ if (timespec64_compare(&wall_time, &boot_offset) < 0)
+ boot_offset = (struct timespec64){0};
+
+ /*
+ * We want set wall_to_mono, so the following is true:
+ * wall time + wall_to_mono = boot time
+ */
+ wall_to_mono = timespec64_sub(boot_offset, wall_time);
+
raw_spin_lock_irqsave(&timekeeper_lock, flags);
write_seqcount_begin(&tk_core.seq);
ntp_init();
@@ -1552,13 +1556,10 @@ void __init timekeeping_init(void)
clock->enable(clock);
tk_setup_internals(tk, clock);
- tk_set_xtime(tk, &now);
+ tk_set_xtime(tk, &wall_time);
tk->raw_sec = 0;
- if (boot.tv_sec == 0 && boot.tv_nsec == 0)
- boot = tk_xtime(tk);
- set_normalized_timespec64(&tmp, -boot.tv_sec, -boot.tv_nsec);
- tk_set_wall_to_mono(tk, tmp);
+ tk_set_wall_to_mono(tk, wall_to_mono);
timekeeping_update(tk, TK_MIRROR | TK_CLOCK_WAS_SET);
--
2.18.0
next prev parent reply other threads:[~2018-07-12 0:07 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-12 0:04 [PATCH v13 00/18] Early boot time stamps Pavel Tatashin
2018-07-12 0:04 ` [PATCH v13 01/18] x86: text_poke() may access uninitialized struct pages Pavel Tatashin
2018-07-12 0:04 ` [PATCH v13 02/18] x86: initialize static branching early Pavel Tatashin
2018-07-12 0:04 ` [PATCH v13 03/18] x86/CPU: Call detect_nopl() only on the BSP Pavel Tatashin
2018-07-12 0:04 ` [PATCH v13 04/18] x86/tsc: redefine notsc to behave as tsc=unstable Pavel Tatashin
2018-07-12 0:04 ` [PATCH v13 05/18] kvm/x86: remove kvm memblock dependency Pavel Tatashin
2018-07-12 0:04 ` [PATCH v13 06/18] x86/xen/time: initialize pv xen time in init_hypervisor_platform Pavel Tatashin
2018-07-13 1:57 ` Pavel Tatashin
2018-07-17 15:28 ` Boris Ostrovsky
2018-07-18 1:38 ` Pavel Tatashin
2018-07-12 0:04 ` [PATCH v13 07/18] x86/xen/time: output xen sched_clock time from 0 Pavel Tatashin
2018-07-17 15:43 ` Boris Ostrovsky
2018-07-18 1:59 ` Pavel Tatashin
2018-07-12 0:04 ` [PATCH v13 08/18] s390/time: add read_persistent_wall_and_boot_offset() Pavel Tatashin
2018-07-12 0:04 ` Pavel Tatashin [this message]
2018-07-12 0:04 ` [PATCH v13 10/18] time: default boot time offset to local_clock() Pavel Tatashin
2018-07-12 0:04 ` [PATCH v13 11/18] s390/time: remove read_boot_clock64() Pavel Tatashin
2018-07-12 0:04 ` [PATCH v13 12/18] ARM/time: " Pavel Tatashin
2018-07-12 0:04 ` [PATCH v13 13/18] x86/tsc: calibrate tsc only once Pavel Tatashin
2018-07-13 7:22 ` Dou Liyang
2018-07-13 11:30 ` Pavel Tatashin
2018-07-16 9:32 ` Dou Liyang
2018-07-16 13:35 ` Pavel Tatashin
2018-07-17 8:59 ` Dou Liyang
2018-07-17 14:36 ` Pavel Tatashin
2018-07-12 0:04 ` [PATCH v13 14/18] x86/tsc: initialize cyc2ns when tsc freq. is determined Pavel Tatashin
2018-07-13 9:11 ` Dou Liyang
2018-07-13 11:39 ` Pavel Tatashin
2018-07-12 0:04 ` [PATCH v13 15/18] x86/tsc: use tsc early Pavel Tatashin
2018-07-12 0:04 ` [PATCH v13 16/18] sched: move sched clock initialization and merge with generic clock Pavel Tatashin
2018-07-12 23:50 ` kbuild test robot
2018-07-12 0:04 ` [PATCH v13 17/18] sched: early boot clock Pavel Tatashin
2018-07-12 0:04 ` [PATCH v13 18/18] sched: use static key for sched_clock_running Pavel Tatashin
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