From: Stephen Hemminger <shemminger@osdl.org>
To: john stultz <johnstul@us.ibm.com>,
Linus Torvalds <torvalds@osdl.org>,
Andrew Morton <akpm@digeo.com>
Cc: linux-kernel@vger.kernel.org
Subject: [PATCH] monotonic seqlock for HPET timer
Date: Wed, 8 Oct 2003 11:58:20 -0700 [thread overview]
Message-ID: <20031008115820.435c97c1.shemminger@osdl.org> (raw)
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
It builds and runs, but I don't have hardware with HPET 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_hpet.c linux-2.5-net/arch/i386/kernel/timers/timer_hpet.c
--- linux-2.5/arch/i386/kernel/timers/timer_hpet.c 2003-09-30 13:53:48.000000000 -0700
+++ linux-2.5-net/arch/i386/kernel/timers/timer_hpet.c 2003-09-16 12:54:26.000000000 -0700
@@ -24,7 +24,7 @@
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:
@@ -57,12 +57,14 @@
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);
- 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);
@@ -99,7 +101,7 @@
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 @@
/* 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)
next reply other threads:[~2003-10-08 19:00 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-10-08 18:58 Stephen Hemminger [this message]
2003-10-09 0:15 [PATCH] monotonic seqlock for HPET timer Pallipadi, Venkatesh
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