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timekeeping: Replace read_boot_clock64() with read_persistent_wall_and_boot_offset() 

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>
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/20180719205545.16512-16-pasha.tatashin@oracle.com
This commit is contained in:
Pavel Tatashin 2018-07-19 16:55:34 -04:00 committed by Thomas Gleixner
parent be2e0e4257
commit 3eca993740
2 changed files with 31 additions and 29 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
include/linux/timekeeping.h
View File

@ -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);
/*

57
kernel/time/timekeeping.c
View File

@ -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)
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;
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;
} 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);