Re: [RFC PATCH v2 0/3] Deduplicate RISCV cmpxchg.h and atomic.c macros

[Guo Ren]

On Thu, Aug 3, 2023 at 1:14 PM Leonardo Bras <leobras@xxxxxxxxxx> wrote:
>
> I unified previous patchsets into a single one, since the work is related.
>
> 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.
>
> Note to Guo Ren:
> I did some further improvement after your previous reviews, so I ended
> up afraid including your Reviewed-by before cheching if the changes are
> ok for you. Please check it out again, I just removed some helper macros
> that were not being used elsewhere in the kernel.
I found this optimization has conflicts with the below patches:
https://lore.kernel.org/linux-riscv/20230802164701.192791-15-guoren@xxxxxxxxxx/
https://lore.kernel.org/linux-riscv/20230802164701.192791-5-guoren@xxxxxxxxxx/

If yours merged, how do we support the inline cmpxchg/xchg_small
function? It's very struggling to use macros to implement complex
functions.

Could you consider a more relaxed optimization in which we could
insert inline cmpxchg/xchg_small?

>
> Thanks!
> Leo
>
>
> Changes since squashed cmpxchg:
> - 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.
>
> 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@xxxxxxxxxx/
>
> 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@xxxxxxxxxx/
>
> 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@xxxxxxxxxx/
>
>
> Leonardo Bras (3):
>   riscv/cmpxchg: Deduplicate xchg() asm functions
>   riscv/cmpxchg: Deduplicate cmpxchg() asm and macros
>   riscv/atomic.h : Deduplicate arch_atomic.*
>
>  arch/riscv/include/asm/atomic.h  | 164 ++++++++--------
>  arch/riscv/include/asm/cmpxchg.h | 318 +++++--------------------------
>  2 files changed, 123 insertions(+), 359 deletions(-)
>
> --
> 2.41.0
>


-- 
Best Regards
 Guo Ren