Ingo, All,
As requested, here is a quick patch that converts the rwlock_t
monotonic_lock (which protects the monotonic_base value used in
monotonic_clock()) to a seqlock.
Let me know if you have any comments.
thanks
-john
diff -Nru a/arch/i386/kernel/timers/timer_cyclone.c b/arch/i386/kernel/timers/timer_cyclone.c
--- a/arch/i386/kernel/timers/timer_cyclone.c Mon Jun 2 19:01:13 2003
+++ b/arch/i386/kernel/timers/timer_cyclone.c Mon Jun 2 19:01:13 2003
@@ -36,7 +36,7 @@
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) \
@@ -52,7 +52,7 @@
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);
@@ -77,7 +77,7 @@
/* 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;
@@ -118,12 +118,16 @@
u32 now_low, now_high;
unsigned long long last_offset, this_offset, base;
unsigned long long ret;
+ unsigned long 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);
diff -Nru a/arch/i386/kernel/timers/timer_tsc.c b/arch/i386/kernel/timers/timer_tsc.c
--- a/arch/i386/kernel/timers/timer_tsc.c Mon Jun 2 19:01:13 2003
+++ b/arch/i386/kernel/timers/timer_tsc.c Mon Jun 2 19:01:13 2003
@@ -30,7 +30,7 @@
static unsigned long last_tsc_low; /* lsb 32 bits of Time Stamp Counter */
static unsigned long last_tsc_high; /* msb 32 bits of Time Stamp Counter */
static unsigned long long monotonic_base;
-static rwlock_t monotonic_lock = RW_LOCK_UNLOCKED;
+static seqlock_t monotonic_lock = SEQLOCK_UNLOCKED;
/* convert from cycles(64bits) => nanoseconds (64bits)
* basic equation:
@@ -102,12 +102,15 @@
static unsigned long long monotonic_clock_tsc(void)
{
unsigned long long last_offset, this_offset, base;
-
+ unsigned long seq;
+
/* atomically read monotonic base & last_offset */
- read_lock_irq(&monotonic_lock);
- last_offset = ((unsigned long long)last_tsc_high<<32)|last_tsc_low;
- base = monotonic_base;
- read_unlock_irq(&monotonic_lock);
+ do {
+ seq = read_seqbegin(&monotonic_lock);
+
+ last_offset = ((unsigned long long)last_tsc_high<<32)|last_tsc_low;
+ base = monotonic_base;
+ } while (read_seqretry(&monotonic_lock, seq));
/* Read the Time Stamp Counter */
rdtscll(this_offset);
@@ -125,7 +128,7 @@
static int count1 = 0;
unsigned long long this_offset, last_offset;
- write_lock(&monotonic_lock);
+ write_seqlock(&monotonic_lock);
last_offset = ((unsigned long long)last_tsc_high<<32)|last_tsc_low;
/*
* It is important that these two operations happen almost at
@@ -184,7 +187,7 @@
/* update the monotonic base value */
this_offset = ((unsigned long long)last_tsc_high<<32)|last_tsc_low;
monotonic_base += cycles_2_ns(this_offset - last_offset);
- write_unlock(&monotonic_lock);
+ write_sequnlock(&monotonic_lock);
/* calculate delay_at_last_interrupt */
count = ((LATCH-1) - count) * TICK_SIZE;