Commit 43fc52f3 authored by Stephen Hemminger's avatar Stephen Hemminger Committed by Linus Torvalds

[PATCH] monotonic seqlock for HPET timer

Replace read/write lock used for HPET timer monotonic_lock with seqlock.
Similar to locking used on xtime and monotonic_lock in timers/timer_tsc.c
parent 639a2b25
......@@ -24,7 +24,7 @@ static unsigned long hpet_last; /* hpet counter value at last tick*/
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:
......@@ -57,12 +57,14 @@ static inline unsigned long long cycles_2_ns(unsigned long long cyc)
static unsigned long long monotonic_clock_hpet(void)
{
unsigned long long last_offset, this_offset, base;
unsigned seq;
/* atomically read monotonic base & last_offset */
read_lock_irq(&monotonic_lock);
do {
seq = read_seqbegin(&monotonic_lock);
last_offset = ((unsigned long long)last_tsc_high<<32)|last_tsc_low;
base = monotonic_base;
read_unlock_irq(&monotonic_lock);
} while (read_seqretry(&monotonic_lock, seq));
/* Read the Time Stamp Counter */
rdtscll(this_offset);
......@@ -99,7 +101,7 @@ static void mark_offset_hpet(void)
unsigned long long this_offset, last_offset;
unsigned long offset;
write_lock(&monotonic_lock);
write_seqlock(&monotonic_lock);
last_offset = ((unsigned long long)last_tsc_high<<32)|last_tsc_low;
rdtsc(last_tsc_low, last_tsc_high);
......@@ -113,7 +115,7 @@ static void mark_offset_hpet(void)
/* 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);
}
void delay_hpet(unsigned long loops)
......
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