Subject: [PATCH 00/10] locking: Introduce local{,64}_try_cmpxchg

From: Uros Bizjak <[email-masked]>
Date: Sun, 5 Mar 2023 21:56:18 +0100

Add generic and target specific support for local{,64}_try_cmpxchg
and wire up support for all targets that use local_t infrastructure.

The patch enables x86 targets to emit special instruction for
local_try_cmpxchg and also local64_try_cmpxchg for x86_64.

The last patch changes __perf_output_begin in events/ring_buffer
to use new locking primitive and improves code from

     4b3:	48 8b 82 e8 00 00 00 	mov    0xe8(%rdx),%rax
     4ba:	48 8b b8 08 04 00 00 	mov    0x408(%rax),%rdi
     4c1:	8b 42 1c             	mov    0x1c(%rdx),%eax
     4c4:	48 8b 4a 28          	mov    0x28(%rdx),%rcx
     4c8:	85 c0                	test   %eax,%eax
     ...
     4ef:	48 89 c8             	mov    %rcx,%rax
     4f2:	48 0f b1 7a 28       	cmpxchg %rdi,0x28(%rdx)
     4f7:	48 39 c1             	cmp    %rax,%rcx
     4fa:	75 b7                	jne    4b3 <...>

to

     4b2:	48 8b 4a 28          	mov    0x28(%rdx),%rcx
     4b6:	48 8b 82 e8 00 00 00 	mov    0xe8(%rdx),%rax
     4bd:	48 8b b0 08 04 00 00 	mov    0x408(%rax),%rsi
     4c4:	8b 42 1c             	mov    0x1c(%rdx),%eax
     4c7:	85 c0                	test   %eax,%eax
     ...
     4d4:	48 89 c8             	mov    %rcx,%rax
     4d7:	48 0f b1 72 28       	cmpxchg %rsi,0x28(%rdx)
     4dc:	0f 85 d0 00 00 00    	jne    5b2 <...>
     ...
     5b2:	48 89 c1             	mov    %rax,%rcx
     5b5:	e9 fc fe ff ff       	jmp    4b6 <...>

Please note that in addition to removed compare, the load from
0x28(%rdx) gets moved out of the loop and the code is rearranged
according to likely/unlikely tags in the source.

Cc: Richard Henderson <[email-masked]>
Cc: Ivan Kokshaysky <[email-masked]>
Cc: Matt Turner <[email-masked]>
Cc: Huacai Chen <[email-masked]>
Cc: WANG Xuerui <[email-masked]>
Cc: Thomas Bogendoerfer <[email-masked]>
Cc: Michael Ellerman <[email-masked]>
Cc: Nicholas Piggin <[email-masked]>
Cc: Christophe Leroy <[email-masked]>
Cc: Thomas Gleixner <[email-masked]>
Cc: Ingo Molnar <[email-masked]>
Cc: Borislav Petkov <[email-masked]>
Cc: Dave Hansen <[email-masked]>
Cc: [email-masked]
Cc: "H. Peter Anvin" <[email-masked]>
Cc: Arnd Bergmann <[email-masked]>
Cc: Peter Zijlstra <[email-masked]>
Cc: Arnaldo Carvalho de Melo <[email-masked]>
Cc: Mark Rutland <[email-masked]>
Cc: Alexander Shishkin <[email-masked]>
Cc: Jiri Olsa <[email-masked]>
Cc: Namhyung Kim <[email-masked]>
Cc: Ian Rogers <[email-masked]>
Cc: Will Deacon <[email-masked]>
Cc: Boqun Feng <[email-masked]>
Cc: Jiaxun Yang <[email-masked]>
Cc: Jun Yi <[email-masked]>

Uros Bizjak (10):
  locking/atomic: Add missing cast to try_cmpxchg() fallbacks
  locking/atomic: Add generic try_cmpxchg{,64}_local support
  locking/alpha: Wire up local_try_cmpxchg
  locking/loongarch: Wire up local_try_cmpxchg
  locking/mips: Wire up local_try_cmpxchg
  locking/powerpc: Wire up local_try_cmpxchg
  locking/x86: Wire up local_try_cmpxchg
  locking/generic: Wire up local{,64}_try_cmpxchg
  locking/x86: Enable local{,64}_try_cmpxchg
  perf/ring_buffer: use local_try_cmpxchg in __perf_output_begin

 arch/alpha/include/asm/local.h              |  2 ++
 arch/loongarch/include/asm/local.h          |  2 ++
 arch/mips/include/asm/local.h               |  2 ++
 arch/powerpc/include/asm/local.h            | 11 ++++++
 arch/x86/include/asm/cmpxchg.h              |  6 ++++
 arch/x86/include/asm/local.h                |  2 ++
 include/asm-generic/local.h                 |  1 +
 include/asm-generic/local64.h               |  2 ++
 include/linux/atomic/atomic-arch-fallback.h | 40 ++++++++++++++++-----
 include/linux/atomic/atomic-instrumented.h  | 20 ++++++++++-
 kernel/events/ring_buffer.c                 |  5 +--
 scripts/atomic/gen-atomic-fallback.sh       |  6 +++-
 scripts/atomic/gen-atomic-instrumented.sh   |  2 +-
 13 files changed, 87 insertions(+), 14 deletions(-)

-- 
2.39.2