Messages in this thread Patch in this message | | | From | Uros Bizjak <> | Subject | [PATCH v2] x86/ACPI/boot: Improve __acpi_acquire_global_lock | Date | Mon, 20 Mar 2023 22:20:12 +0100 |
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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 <ubizjak@gmail.com> Cc: "Rafael J. Wysocki" <rafael@kernel.org> Cc: Len Brown <lenb@kernel.org> 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> --- v2: Expand return statement. --- 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 1c38174b5f01..a08a4a7a03f8 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) -- 2.39.2
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