| Message ID | 20230227164745.339269-1-ubizjak@gmail.com |
|---|---|
| State | Superseded |
| Headers | show |
| Series | x86/ACPI/boot: Improve __acpi_acquire_global_lock | expand |
On Mon, Feb 27, 2023 at 5:48 PM Uros Bizjak <ubizjak@gmail.com> wrote: > > 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> > --- > arch/x86/kernel/acpi/boot.c | 7 ++++--- > 1 file changed, 4 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c > index 1c38174b5f01..577403c69983 100644 > --- a/arch/x86/kernel/acpi/boot.c > +++ b/arch/x86/kernel/acpi/boot.c > @@ -1853,13 +1853,14 @@ 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; > + return val ? 0 : -1; I would prefer if (val) return -1; return 0; > } > > int __acpi_release_global_lock(unsigned int *lock) > -- Otherwise I agree that this change would be an improvement. >
diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c index 1c38174b5f01..577403c69983 100644 --- a/arch/x86/kernel/acpi/boot.c +++ b/arch/x86/kernel/acpi/boot.c @@ -1853,13 +1853,14 @@ 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; + return val ? 0 : -1; } int __acpi_release_global_lock(unsigned int *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 <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> --- arch/x86/kernel/acpi/boot.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)