[RFC PATCH v5 0/5] Rework & improve riscv cmpxchg.h and atomic.h

[Guo Ren]

On Thu, Aug 10, 2023 at 01:03:42AM -0300, Leonardo Bras wrote:
> 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, merged with guoren/qspinlock_v11 and
> booted just fine with qemu -machine virt -append "qspinlock". 
> 
> (tree: https://gitlab.com/LeoBras/linux/-/commits/guo_qspinlock_v11)
Tested-by: Guo Ren <guoren at kernel.org>

Sorry for late reply, because we are stress testing CNA qspinlock on
sg2042 128 cores hardware platform. This series has passed our test for
several weeks. For more detail, ref:
https://lore.kernel.org/linux-riscv/20230910082911.3378782-1-guoren@kernel.org/

> 
> Thanks!
> Leo
> 
> Changes since squashed cmpxchg RFCv4:
> - Added (__typeof__(*(p))) before returning from {cmp,}xchg, as done
>   in current upstream, (possibly) fixing the bug from kernel test robot
> https://lore.kernel.org/all/20230809021311.1390578-2-leobras@redhat.com/
> 
> Changes since squashed cmpxchg RFCv3:
> - Fixed bug on cmpxchg macro for var size 1 & 2: now working
> - Macros for var size 1 & 2's lr.w and sc.w now are guaranteed to receive
>   input of a 32-bit aligned address
> - Renamed internal macros from _mask to _masked for patches 4 & 5
> - __rc variable on macros for var size 1 & 2 changed from register to ulong 
> https://lore.kernel.org/all/20230804084900.1135660-2-leobras@redhat.com/
> 
> 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/20230803051401.710236-2-leobras@redhat.com/
> 
> 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/20230419062505.257231-1-leobras@redhat.com/
> https://lore.kernel.org/all/20230406082018.70367-1-leobras@redhat.com/
> 
> Changes since (cmpxchg) RFCv3:
> - Squashed the 6 original patches in 2: one for cmpxchg and one for xchg
> https://lore.kernel.org/all/20230404163741.2762165-1-leobras@redhat.com/
> 
> 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/20230321074249.2221674-1-leobras@redhat.com/
> 
> Changes since (cmpxchg) RFCv1:
> - Fixed patch 4/6 suffix from 'w.aqrl' to '.w.aqrl', to avoid build error
> https://lore.kernel.org/all/20230318080059.1109286-1-leobras@redhat.com/
> 
> 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 | 404 ++++++++++---------------------
>  2 files changed, 200 insertions(+), 368 deletions(-)
> 
> 
> base-commit: cacc6e22932f373a91d7be55a9b992dc77f4c59b
> -- 
> 2.41.0
> 
> 
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