From 22767544e9763e82acb60c233051bc426381b61c Mon Sep 17 00:00:00 2001 From: Uros Bizjak Date: Mon, 20 Mar 2023 22:20:12 +0100 Subject: [PATCH] x86/ACPI/boot: Improve __acpi_acquire_global_lock Improve __acpi_acquire_global_lock by using a temporary variable. This enables compiler to perform if-conversion and improves generated code from: ... 72a: d1 ea shr %edx 72c: 83 e1 fc and $0xfffffffc,%ecx 72f: 83 e2 01 and $0x1,%edx 732: 09 ca or %ecx,%edx 734: 83 c2 02 add $0x2,%edx 737: f0 0f b1 17 lock cmpxchg %edx,(%rdi) 73b: 75 e9 jne 726 <__acpi_acquire_global_lock+0x6> 73d: 83 e2 03 and $0x3,%edx 740: 31 c0 xor %eax,%eax 742: 83 fa 03 cmp $0x3,%edx 745: 0f 95 c0 setne %al 748: f7 d8 neg %eax to: ... 72a: d1 e9 shr %ecx 72c: 83 e2 fc and $0xfffffffc,%edx 72f: 83 e1 01 and $0x1,%ecx 732: 09 ca or %ecx,%edx 734: 83 c2 02 add $0x2,%edx 737: f0 0f b1 17 lock cmpxchg %edx,(%rdi) 73b: 75 e9 jne 726 <__acpi_acquire_global_lock+0x6> 73d: 8d 41 ff lea -0x1(%rcx),%eax BTW: the compiler could generate: lea 0x2(%rcx,%rdx,1),%edx instead of: or %ecx,%edx add $0x2,%edx but unwated conversion from add to or when bits are known to be zero prevents this improvement. This is GCC PR108477. No functional change intended. Signed-off-by: Uros Bizjak Signed-off-by: Dave Hansen Acked-by: Rafael J. Wysocki Link: https://lore.kernel.org/all/20230320212012.12704-1-ubizjak%40gmail.com --- arch/x86/kernel/acpi/boot.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c index 1c38174..a08a4a7 100644 --- a/arch/x86/kernel/acpi/boot.c +++ b/arch/x86/kernel/acpi/boot.c @@ -1853,13 +1853,18 @@ early_param("acpi_sci", setup_acpi_sci); int __acpi_acquire_global_lock(unsigned int *lock) { - unsigned int old, new; + unsigned int old, new, val; old = READ_ONCE(*lock); do { - new = (((old & ~0x3) + 2) + ((old >> 1) & 0x1)); + val = (old >> 1) & 0x1; + new = (old & ~0x3) + 2 + val; } while (!try_cmpxchg(lock, &old, new)); - return ((new & 0x3) < 3) ? -1 : 0; + + if (val) + return 0; + + return -1; } int __acpi_release_global_lock(unsigned int *lock) -- 2.7.4