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Subject[PATCH v2 1/3] timekeeping: Add persistent_clock_exist flag
Date
In current kernel, there are several places which need to check
whether there is a persistent clock for the platform. Current check
is done by calling the read_persistent_clock() and validating its
return value.

So one optimization is to do the check only once in timekeeping_init(),
and use a flag persistent_clock_exist to record it.

v2: Add a has_persistent_clock() helper function, as suggested by John.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: John Stultz <john.stultz@linaro.org>
Signed-off-by: Feng Tang <feng.tang@intel.com>
---
include/linux/time.h | 6 ++++++
kernel/time/timekeeping.c | 16 +++++++++++-----
2 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/include/linux/time.h b/include/linux/time.h
index 4d358e9..2f58603 100644
--- a/include/linux/time.h
+++ b/include/linux/time.h
@@ -115,6 +115,12 @@ static inline bool timespec_valid_strict(const struct timespec *ts)
return true;
}

+extern bool persistent_clock_exist;
+static inline bool has_persistent_clock(void)
+{
+ return persistent_clock_exist;
+}
+
extern void read_persistent_clock(struct timespec *ts);
extern void read_boot_clock(struct timespec *ts);
extern int update_persistent_clock(struct timespec now);
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index cbc6acb..2fd3aed 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -29,6 +29,9 @@ static struct timekeeper timekeeper;
/* flag for if timekeeping is suspended */
int __read_mostly timekeeping_suspended;

+/* Flag for if there is a persistent clock on this platform */
+bool __read_mostly persistent_clock_exist = false;
+
static inline void tk_normalize_xtime(struct timekeeper *tk)
{
while (tk->xtime_nsec >= ((u64)NSEC_PER_SEC << tk->shift)) {
@@ -640,12 +643,14 @@ void __init timekeeping_init(void)
struct timespec now, boot, tmp;

read_persistent_clock(&now);
+
if (!timespec_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_exist = true;

read_boot_clock(&boot);
if (!timespec_valid_strict(&boot)) {
@@ -718,11 +723,12 @@ void timekeeping_inject_sleeptime(struct timespec *delta)
{
struct timekeeper *tk = &timekeeper;
unsigned long flags;
- struct timespec ts;

- /* Make sure we don't set the clock twice */
- read_persistent_clock(&ts);
- if (!(ts.tv_sec == 0 && ts.tv_nsec == 0))
+ /*
+ * Make sure we don't set the clock twice, as timekeeping_resume()
+ * already did it
+ */
+ if (has_persistent_clock())
return;

write_seqlock_irqsave(&tk->lock, flags);
--
1.7.9.5


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