[RFC,v3,0/5] Rework & improve riscv cmpxchg.h and atomic.h

Message

Leonardo Bras Aug. 4, 2023, 8:48 a.m. UTC

While studying riscv's cmpxchg.h file, I got really interested in
understanding how RISCV asm implemented the different versions of
{cmp,}xchg.

When I understood the pattern, it made sense for me to remove the
duplications and create macros to make it easier to understand what exactly
changes between the versions: Instruction sufixes & barriers.

Also, did the same kind of work on atomic.c.

After that, I noted both cmpxchg and xchg only accept variables of 
size 4 and 8, compared to x86 and arm64 which do 1,2,4,8.

Now that deduplication is done, it is quite direct to implement them
for variable sizes 1 and 2, so I did it. Then Guo Ren already presented
me some possible users :)

I did compare the generated asm on a test.c that contained usage for every
changed function, and could not detect any change on patches 1 + 2 + 3 
compared with upstream.

Pathes 4 & 5 were compiled-tested, but I could not run-test them yet.

Thanks!
Leo


Changes since squashed cmpxchg RFCv2:
- Removed rc parameter from the new macro: it can be internal to the macro
- 2 new patches: cmpxchg size 1 and 2, xchg size 1 and 2
https://lore.kernel.org/all/[e-mail]/

Changes since squashed cmpxchg RFCv1:
- Unified with atomic.c patchset
- Rebased on top of torvalds/master (thanks Andrea Parri!)
- Removed helper macros that were not being used elsewhere in the kernel.
https://lore.kernel.org/all/[e-mail]/
https://lore.kernel.org/all/[e-mail]/

Changes since (cmpxchg) RFCv3:
- Squashed the 6 original patches in 2: one for cmpxchg and one for xchg
https://lore.kernel.org/all/[e-mail]/

Changes since (cmpxchg) RFCv2:
- Fixed  macros that depend on having a local variable with a magic name
- Previous cast to (long) is now only applied on 4-bytes cmpxchg
https://lore.kernel.org/all/[e-mail]/

Changes since (cmpxchg) RFCv1:
- Fixed patch 4/6 suffix from 'w.aqrl' to '.w.aqrl', to avoid build error
https://lore.kernel.org/all/[e-mail]/


Leonardo Bras (5):
  riscv/cmpxchg: Deduplicate xchg() asm functions
  riscv/cmpxchg: Deduplicate cmpxchg() asm and macros
  riscv/atomic.h : Deduplicate arch_atomic.*
  riscv/cmpxchg: Implement cmpxchg for variables of size 1 and 2
  riscv/cmpxchg: Implement xchg for variables of size 1 and 2

 arch/riscv/include/asm/atomic.h  | 164 ++++++-------
 arch/riscv/include/asm/cmpxchg.h | 393 ++++++++++---------------------
 2 files changed, 195 insertions(+), 362 deletions(-)