mirrors/linux
2
0
Fork 0
mirror of https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git synced 2026-05-09 10:11:52 -04:00
Code Issues Packages Projects Releases Wiki Activity

x86/percpu: Rewrite arch_raw_cpu_ptr() to be easier for compilers to optimize

Browse Source 
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 on a test build, a -1.3% reduction.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Uros Bizjak <ubizjak@gmail.com>
Cc: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20231015202523.189168-1-ubizjak@gmail.com
This commit is contained in:
Uros Bizjak
2023-10-15 22:24:39 +02:00
committed by Ingo Molnar
parent e29aad08b1
commit a048d3abae
1 changed files with 4 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files

6
arch/x86/include/asm/percpu.h
View File

@@ -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 */