The following commit has been merged into the locking/core branch of tip:
Commit-ID: 890a0794b34f89fcd90e94ec970ad2bc18b70e73
Gitweb: https://git.kernel.org/tip/890a0794b34f89fcd90e94ec970ad2bc18b70e73
Author: Uros Bizjak <ubizjak@xxxxxxxxx>
AuthorDate: Mon, 16 Jan 2023 17:25:22 +01:00
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Thu, 26 Jan 2023 11:49:40 +01:00
x86/ACPI/boot: Use try_cmpxchg() in __acpi_{acquire,release}_global_lock()
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 MOV 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@xxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Link: https://lore.kernel.org/r/20230116162522.4072-1-ubizjak@xxxxxxxxx
---
arch/x86/kernel/acpi/boot.c | 16 ++++++++--------
1 file changed, 8 insertions(+), 8 deletions(-)
diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c
index 907cc98..4177577 100644
--- a/arch/x86/kernel/acpi/boot.c
+++ b/arch/x86/kernel/acpi/boot.c
@@ -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;
}
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