[v1,0/5] Rework & improve riscv cmpxchg.h and atomic.h

Message

Leonardo Bras Jan. 3, 2024, 4:31 p.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, 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)

Latest tests happened based on this tree:
https://github.com/guoren83/linux/tree/qspinlock_v12

Thanks!
Leo

Changes since squashed cmpxchg RFCv5:
- Resend as v1
https://lore.kernel.org/all/[e-mail]/

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/[e-mail]/

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/[e-mail]/

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 | 404 ++++++++++---------------------
 2 files changed, 200 insertions(+), 368 deletions(-)


base-commit: 610a9b8f49fbcf1100716370d3b5f6f884a2835a

Comments

Leonardo Bras Jan. 3, 2024, 4:34 p.m. UTC | #1

On Wed, Jan 03, 2024 at 01:31:58PM -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)
> 
> Latest tests happened based on this tree:
> https://github.com/guoren83/linux/tree/qspinlock_v12
> 
> Thanks!
> Leo
> 
> Changes since squashed cmpxchg RFCv5:
> - Resend as v1

Oh, forgot to mention:
I added some of Reviewed-by that were missing.
Thanks Guo Ren!


> https://lore.kernel.org/all/[e-mail]/
> 
> 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/[e-mail]/
> 
> 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/[e-mail]/
> 
> 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 | 404 ++++++++++---------------------
>  2 files changed, 200 insertions(+), 368 deletions(-)
> 
> 
> base-commit: 610a9b8f49fbcf1100716370d3b5f6f884a2835a
> -- 
> 2.43.0
>

[e-mail] April 10, 2024, 2:20 p.m. UTC | #2

Hello:

This series was applied to riscv/linux.git (for-next)
by Palmer Dabbelt <[e-mail]>:

On Wed,  3 Jan 2024 13:31:58 -0300 you 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.
> 
> [...]

Here is the summary with links:
  - [v1,1/5] riscv/cmpxchg: Deduplicate xchg() asm functions
    https://git.kernel.org/riscv/c/4bfa185fe3f0
  - [v1,2/5] riscv/cmpxchg: Deduplicate cmpxchg() asm and macros
    https://git.kernel.org/riscv/c/07a0a41cb77d
  - [v1,3/5] riscv/atomic.h : Deduplicate arch_atomic.*
    https://git.kernel.org/riscv/c/906123739272
  - [v1,4/5] riscv/cmpxchg: Implement cmpxchg for variables of size 1 and 2
    https://git.kernel.org/riscv/c/54280ca64626
  - [v1,5/5] riscv/cmpxchg: Implement xchg for variables of size 1 and 2
    https://git.kernel.org/riscv/c/a8ed2b7a2c13

You are awesome, thank you!