[PATCH -tip 1/3] x86/percpu: Rewrite arch_raw_cpu_ptr()

[Uros Bizjak]

Implement arch_raw_cpu_ptr() as a load from this_cpu_off and then
add the ptr value to the base. This way, the compiler can propagate
addend to the following instruction and simplify address calculation.

E.g.: address calcuation in amd_pmu_enable_virt() improves from:

    48 c7 c0 00 00 00 00 	mov    $0x0,%rax
	87b7: R_X86_64_32S	cpu_hw_events

    65 48 03 05 00 00 00 	add    %gs:0x0(%rip),%rax
    00
	87bf: R_X86_64_PC32	this_cpu_off-0x4

    48 c7 80 28 13 00 00 	movq   $0x0,0x1328(%rax)
    00 00 00 00

to:

    65 48 8b 05 00 00 00 	mov    %gs:0x0(%rip),%rax
    00
	8798: R_X86_64_PC32	this_cpu_off-0x4
    48 c7 80 00 00 00 00 	movq   $0x0,0x0(%rax)
    00 00 00 00
	87a6: R_X86_64_32S	cpu_hw_events+0x1328

The compiler also eliminates additional redundant loads from
this_cpu_off, reducing the number of percpu offset reads
from 1668 to 1646.

Cc: Nadav Amit <namit@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Signed-off-by: Uros Bizjak <ubizjak@xxxxxxxxx>
---
 arch/x86/include/asm/percpu.h | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h
index 60ea7755c0fe..915675f3ad60 100644
--- a/arch/x86/include/asm/percpu.h
+++ b/arch/x86/include/asm/percpu.h
@@ -56,9 +56,11 @@
 #define arch_raw_cpu_ptr(ptr)					\
 ({								\
 	unsigned long tcp_ptr__;				\
-	asm ("add " __percpu_arg(1) ", %0"			\
+	asm ("mov " __percpu_arg(1) ", %0"			\
 	     : "=r" (tcp_ptr__)					\
-	     : "m" (__my_cpu_var(this_cpu_off)), "0" (ptr));	\
+	     : "m" (__my_cpu_var(this_cpu_off)));		\
+								\
+	tcp_ptr__ += (unsigned long)(ptr);			\
 	(typeof(*(ptr)) __kernel __force *)tcp_ptr__;		\
 })
 #else /* CONFIG_SMP */
-- 
2.41.0