[PATCH] monotonic seqlock for cyclone timer

From: Stephen Hemminger
Date: Wed Oct 08 2003 - 13:59:49 EST


Replace read/write lock used for cyclone timer monotonic_lock with seqlock.
Similar to locking used on xtime and monotonic_lock in timers/timer_tsc.c

It builds and runs, but I don't have hardware with cyclone support to test.
Not a big deal (yet) since only hangcheck timer uses monotonic clock so far.

diff -urN -X dontdiff linux-2.5/arch/i386/kernel/timers/timer_cyclone.c linux-2.5-net/arch/i386/kernel/timers/timer_cyclone.c
--- linux-2.5/arch/i386/kernel/timers/timer_cyclone.c 2003-09-30 13:53:48.000000000 -0700
+++ linux-2.5-net/arch/i386/kernel/timers/timer_cyclone.c 2003-09-16 12:54:05.000000000 -0700
@@ -35,7 +35,7 @@
static u32 last_cyclone_low;
static u32 last_cyclone_high;
static unsigned long long monotonic_base;
-static rwlock_t monotonic_lock = RW_LOCK_UNLOCKED;
+static seqlock_t monotonic_lock = SEQLOCK_UNLOCKED;

/* helper macro to atomically read both cyclone counter registers */
#define read_cyclone_counter(low,high) \
@@ -51,7 +51,7 @@
int count;
unsigned long long this_offset, last_offset;

- write_lock(&monotonic_lock);
+ write_seqlock(&monotonic_lock);
last_offset = ((unsigned long long)last_cyclone_high<<32)|last_cyclone_low;

spin_lock(&i8253_lock);
@@ -76,7 +76,7 @@
/* update the monotonic base value */
this_offset = ((unsigned long long)last_cyclone_high<<32)|last_cyclone_low;
monotonic_base += (this_offset - last_offset) & CYCLONE_TIMER_MASK;
- write_unlock(&monotonic_lock);
+ write_sequnlock(&monotonic_lock);

/* calculate delay_at_last_interrupt */
count = ((LATCH-1) - count) * TICK_SIZE;
@@ -117,12 +117,15 @@
u32 now_low, now_high;
unsigned long long last_offset, this_offset, base;
unsigned long long ret;
+ unsigned seq;

/* atomically read monotonic base & last_offset */
- read_lock_irq(&monotonic_lock);
- last_offset = ((unsigned long long)last_cyclone_high<<32)|last_cyclone_low;
- base = monotonic_base;
- read_unlock_irq(&monotonic_lock);
+ do {
+ seq = read_seqbegin(&monotonic_lock);
+ last_offset = ((unsigned long long)last_cyclone_high<<32)|last_cyclone_low;
+ base = monotonic_base;
+ } while (read_seqretry(&monotonic_lock, seq));
+

/* Read the cyclone counter */
read_cyclone_counter(now_low,now_high);
-
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