The patch titled
time: fix time going backward w/ clock=pit
has been added to the -mm tree. Its filename is
time-fix-time-going-backward-w-clock=pit.patch
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
------------------------------------------------------
Subject: time: fix time going backward w/ clock=pit
From: john stultz <johnstul@xxxxxxxxxx>
Here is the PIT fix against the TOD patches that Tim pointed out. Many
thanks to Tim for hunting this down.
Cc: Tim Mann <mann@xxxxxxxxxx>
Signed-off-by: John Stultz <johnstul@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---
arch/i386/kernel/i8253.c | 45 ++++++++++++++++++++++++++++++++-----
1 files changed, 39 insertions(+), 6 deletions(-)
diff -puN arch/i386/kernel/i8253.c~time-fix-time-going-backward-w-clock=pit arch/i386/kernel/i8253.c
--- devel/arch/i386/kernel/i8253.c~time-fix-time-going-backward-w-clock=pit 2006-05-25 22:01:22.000000000 -0700
+++ devel-akpm/arch/i386/kernel/i8253.c 2006-05-25 22:01:22.000000000 -0700
@@ -41,9 +41,25 @@ static cycle_t pit_read(void)
{
unsigned long flags;
int count;
- u64 jifs;
+ u32 jifs;
+ static int old_count;
+ static u32 old_jifs;
spin_lock_irqsave(&i8253_lock, flags);
+ /*
+ * Although our caller may have the read side of xtime_lock,
+ * this is now a seqlock, and we are cheating in this routine
+ * by having side effects on state that we cannot undo if
+ * there is a collision on the seqlock and our caller has to
+ * retry. (Namely, old_jifs and old_count.) So we must treat
+ * jiffies as volatile despite the lock. We read jiffies
+ * before latching the timer count to guarantee that although
+ * the jiffies value might be older than the count (that is,
+ * the counter may underflow between the last point where
+ * jiffies was incremented and the point where we latch the
+ * count), it cannot be newer.
+ */
+ jifs = jiffies;
outb_p(0x00, PIT_MODE); /* latch the count ASAP */
count = inb_p(PIT_CH0); /* read the latched count */
count |= inb_p(PIT_CH0) << 8;
@@ -55,12 +71,29 @@ static cycle_t pit_read(void)
outb(LATCH >> 8, PIT_CH0);
count = LATCH - 1;
}
- spin_unlock_irqrestore(&i8253_lock, flags);
- jifs = jiffies_64;
+ /*
+ * It's possible for count to appear to go the wrong way for a
+ * couple of reasons:
+ *
+ * 1. The timer counter underflows, but we haven't handled the
+ * resulting interrupt and incremented jiffies yet.
+ * 2. Hardware problem with the timer, not giving us continuous time,
+ * the counter does small "jumps" upwards on some Pentium systems,
+ * (see c't 95/10 page 335 for Neptun bug.)
+ *
+ * Previous attempts to handle these cases intelligently were
+ * buggy, so we just do the simple thing now.
+ */
+ if (count > old_count && jifs == old_jifs) {
+ count = old_count;
+ }
+ old_count = count;
+ old_jifs = jifs;
+
+ spin_unlock_irqrestore(&i8253_lock, flags);
- jifs -= INITIAL_JIFFIES;
- count = (LATCH-1) - count;
+ count = (LATCH - 1) - count;
return (cycle_t)(jifs * LATCH) + count;
}
@@ -69,7 +102,7 @@ static struct clocksource clocksource_pi
.name = "pit",
.rating = 110,
.read = pit_read,
- .mask = CLOCKSOURCE_MASK(64),
+ .mask = CLOCKSOURCE_MASK(32),
.mult = 0,
.shift = 20,
};
_
Patches currently in -mm which might be from johnstul@xxxxxxxxxx are
time-clocksource-infrastructure.patch
time-clocksource-infrastructure-dont-enable-irq-too-early.patch
time-use-clocksource-infrastructure-for-update_wall_time.patch
time-use-clocksource-infrastructure-for-update_wall_time-mark-few-functions-as-__init.patch
time-let-user-request-precision-from-current_tick_length.patch
time-use-clocksource-abstraction-for-ntp-adjustments.patch
time-use-clocksource-abstraction-for-ntp-adjustments-optimize-out-some-mults-since-gcc-cant-avoid-them.patch
time-introduce-arch-generic-time-accessors.patch
hangcheck-remove-monotomic_clock-on-x86.patch
time-i386-conversion-part-1-move-timer_pitc-to-i8253c.patch
time-i386-conversion-part-2-rework-tsc-support.patch
time-i386-conversion-part-3-enable-generic-timekeeping.patch
time-i386-conversion-part-4-remove-old-timer_opts-code.patch
time-i386-clocksource-drivers.patch
time-i386-clocksource-drivers-pm-timer-doesnt-use-workaround-if-chipset-is-not-buggy.patch
time-i386-clocksource-drivers-pm-timer-doesnt-use-workaround-if-chipset-is-not-buggy-acpi_pm-cleanup.patch
time-i386-clocksource-drivers-pm-timer-doesnt-use-workaround-if-chipset-is-not-buggy-acpi_pm-cleanup-fix-missing-to-rename-pmtmr_good-to-acpi_pm_good.patch
time-i386-clocksource-drivers-fix-spelling-typos.patch
time-rename-clocksource-functions.patch
make-pmtmr_ioport-__read_mostly.patch
generic-time-add-macro-to-simplify-hide-mask.patch
time-fix-time-going-backward-w-clock=pit.patch
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