@@ -1840,23 +1840,23 @@ early_param("acpi_sci", setup_acpi_sci);
int __acpi_acquire_global_lock(unsigned int *lock)
{
- unsigned int old, new, val;
+ unsigned int old, new;
+
+ old = READ_ONCE(*lock);
do {
- old = *lock;
new = (((old & ~0x3) + 2) + ((old >> 1) & 0x1));
- val = cmpxchg(lock, old, new);
- } while (unlikely (val != old));
+ } while (!try_cmpxchg(lock, &old, new));
return ((new & 0x3) < 3) ? -1 : 0;
}
int __acpi_release_global_lock(unsigned int *lock)
{
- unsigned int old, new, val;
+ unsigned int old, new;
+
+ old = READ_ONCE(*lock);
do {
- old = *lock;
new = old & ~0x3;
- val = cmpxchg(lock, old, new);
- } while (unlikely (val != old));
+ } while (!try_cmpxchg(lock, &old, new));
return old & 0x1;
}
Use try_cmpxchg instead of cmpxchg (*ptr, old, new) == old in __acpi_{acquire,release}_global_lock. x86 CMPXCHG instruction returns success in ZF flag, so this change saves a compare after cmpxchg (and related move instruction in front of cmpxchg). Also, try_cmpxchg implicitly assigns old *ptr value to "old" when cmpxchg fails. There is no need to re-read the value in the loop. Note that the value from *ptr should be read using READ_ONCE to prevent the compiler from merging, refetching or reordering the read. No functional change intended. Signed-off-by: Uros Bizjak <ubizjak@gmail.com> Cc: "Rafael J. Wysocki" <rafael@kernel.org> Cc: Len Brown <len.brown@intel.com> Cc: Pavel Machek <pavel@ucw.cz> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: "H. Peter Anvin" <hpa@zytor.com> --- arch/x86/kernel/acpi/boot.c | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-)