Commit-ID: 48cdc135d4840aab8efd2fc3bacb5d7dfd94a9c8
Gitweb: http://git.kernel.org/tip/48cdc135d4840aab8efd2fc3bacb5d7dfd94a9c8
Author: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
AuthorDate: Thu, 21 Feb 2013 22:51:40 +0000
Committer: John Stultz <john.stultz@xxxxxxxxxx>
CommitDate: Thu, 4 Apr 2013 13:18:32 -0700
timekeeping: Implement a shadow timekeeper
Use the shadow timekeeper to do the update_wall_time() adjustments and
then copy it over to the real timekeeper.
Keep the shadow timekeeper in sync when updating stuff outside of
update_wall_time().
This allows us to limit the timekeeper_seq hold time to the update of
the real timekeeper and the vsyscall data in the next patch.
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: John Stultz <john.stultz@xxxxxxxxxx>
---
kernel/time/timekeeping.c | 41 +++++++++++++++++++++++++++++------------
1 file changed, 29 insertions(+), 12 deletions(-)
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 38ac782..d20ffda 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -29,6 +29,7 @@
static struct timekeeper timekeeper;
static DEFINE_RAW_SPINLOCK(timekeeper_lock);
static seqcount_t timekeeper_seq;
+static struct timekeeper shadow_timekeeper;
/* flag for if timekeeping is suspended */
int __read_mostly timekeeping_suspended;
@@ -240,7 +241,7 @@ int pvclock_gtod_unregister_notifier(struct notifier_block *nb)
EXPORT_SYMBOL_GPL(pvclock_gtod_unregister_notifier);
/* must hold timekeeper_lock */
-static void timekeeping_update(struct timekeeper *tk, bool clearntp)
+static void timekeeping_update(struct timekeeper *tk, bool clearntp, bool mirror)
{
if (clearntp) {
tk->ntp_error = 0;
@@ -248,6 +249,9 @@ static void timekeeping_update(struct timekeeper *tk, bool clearntp)
}
update_vsyscall(tk);
update_pvclock_gtod(tk);
+
+ if (mirror)
+ memcpy(&shadow_timekeeper, &timekeeper, sizeof(timekeeper));
}
/**
@@ -504,7 +508,7 @@ int do_settimeofday(const struct timespec *tv)
tk_set_xtime(tk, tv);
- timekeeping_update(tk, true);
+ timekeeping_update(tk, true, true);
write_seqcount_end(&timekeeper_seq);
raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
@@ -548,7 +552,7 @@ int timekeeping_inject_offset(struct timespec *ts)
tk_set_wall_to_mono(tk, timespec_sub(tk->wall_to_monotonic, *ts));
error: /* even if we error out, we forwarded the time, so call update */
- timekeeping_update(tk, true);
+ timekeeping_update(tk, true, true);
write_seqcount_end(&timekeeper_seq);
raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
@@ -628,7 +632,7 @@ static int change_clocksource(void *data)
if (old->disable)
old->disable(old);
}
- timekeeping_update(tk, true);
+ timekeeping_update(tk, true, true);
write_seqcount_end(&timekeeper_seq);
raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
@@ -809,6 +813,8 @@ void __init timekeeping_init(void)
tmp.tv_nsec = 0;
tk_set_sleep_time(tk, tmp);
+ memcpy(&shadow_timekeeper, &timekeeper, sizeof(timekeeper));
+
write_seqcount_end(&timekeeper_seq);
raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
}
@@ -865,7 +871,7 @@ void timekeeping_inject_sleeptime(struct timespec *delta)
__timekeeping_inject_sleeptime(tk, delta);
- timekeeping_update(tk, true);
+ timekeeping_update(tk, true, true);
write_seqcount_end(&timekeeper_seq);
raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
@@ -947,7 +953,7 @@ static void timekeeping_resume(void)
clock->cycle_last = cycle_now;
tk->ntp_error = 0;
timekeeping_suspended = 0;
- timekeeping_update(tk, false);
+ timekeeping_update(tk, false, true);
write_seqcount_end(&timekeeper_seq);
raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
@@ -1328,7 +1334,8 @@ static inline void old_vsyscall_fixup(struct timekeeper *tk)
static void update_wall_time(void)
{
struct clocksource *clock;
- struct timekeeper *tk = &timekeeper;
+ struct timekeeper *real_tk = &timekeeper;
+ struct timekeeper *tk = &shadow_timekeeper;
cycle_t offset;
int shift = 0, maxshift;
unsigned long flags;
@@ -1340,16 +1347,16 @@ static void update_wall_time(void)
if (unlikely(timekeeping_suspended))
goto out;
- clock = tk->clock;
+ clock = real_tk->clock;
#ifdef CONFIG_ARCH_USES_GETTIMEOFFSET
- offset = tk->cycle_interval;
+ offset = real_tk->cycle_interval;
#else
offset = (clock->read(clock) - clock->cycle_last) & clock->mask;
#endif
/* Check if there's really nothing to do */
- if (offset < tk->cycle_interval)
+ if (offset < real_tk->cycle_interval)
goto out;
/*
@@ -1388,12 +1395,22 @@ static void update_wall_time(void)
/* Update clock->cycle_last with the new value */
clock->cycle_last = tk->cycle_last;
- timekeeping_update(tk, false);
+ /*
+ * Update the real timekeeper.
+ *
+ * We could avoid this memcpy by switching pointers, but that
+ * requires changes to all other timekeeper usage sites as
+ * well, i.e. move the timekeeper pointer getter into the
+ * spinlocked/seqcount protected sections. And we trade this
+ * memcpy under the timekeeper_seq against one before we start
+ * updating.
+ */
+ memcpy(real_tk, tk, sizeof(*tk));
+ timekeeping_update(real_tk, false, false);
out:
write_seqcount_end(&timekeeper_seq);
raw_spin_unlock_irqrestore(&timekeeper_lock, flags);
-
}
/**
--
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