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From:   Leonardo Bras Soares Passos <leobras@redhat.com>
Date:   Fri, 4 Aug 2023 05:55:42 -0300
Message-ID: <CAJ6HWG5ps2fZoSM1dPg8TFTLgxZeXGSmjRG5Drg-g0HWH9c3sg@mail.gmail.com>
Subject: Re: [RFC PATCH v2 0/3] Deduplicate RISCV cmpxchg.h and atomic.c macros
To:     Guo Ren <guoren@kernel.org>
Cc:     Will Deacon <will@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Boqun Feng <boqun.feng@gmail.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Andrzej Hajda <andrzej.hajda@intel.com>,
        Arnd Bergmann <arnd@arndb.de>, Ingo Molnar <mingo@kernel.org>,
        Palmer Dabbelt <palmer@rivosinc.com>,
        linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org
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On Fri, Aug 4, 2023 at 5:05=E2=80=AFAM Leonardo Bras Soares Passos
<leobras@redhat.com> wrote:
>
> On Thu, Aug 3, 2023 at 11:29=E2=80=AFPM Guo Ren <guoren@kernel.org> wrote=
:
> >
> > On Fri, Aug 4, 2023 at 10:20=E2=80=AFAM Leonardo Bras Soares Passos
> > <leobras@redhat.com> wrote:
> > >
> > > On Thu, Aug 3, 2023 at 9:53=E2=80=AFPM Guo Ren <guoren@kernel.org> wr=
ote:
> > > >
> > > > On Thu, Aug 3, 2023 at 1:14=E2=80=AFPM Leonardo Bras <leobras@redha=
t.com> 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 wh=
at 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 chang=
es 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=
@kernel.org/
> > > > https://lore.kernel.org/linux-riscv/20230802164701.192791-5-guoren@=
kernel.org/
> > > >
> > > > If yours merged, how do we support the inline cmpxchg/xchg_small
> > > > function?
> > >
> > > Oh, I actually introduced my series so I could introduce new xchg and
> > > cmpxchg for size 1 and 2. Is that what your patches are about, right?
> > >
> > > I was working on that yesterday, and decided to send the patchset
> > > without them because I was still not sure enough.
> > >
> > > About implementation strategy, I was introducing a new macros for xch=
g
> > > & cmpxchg with asm which would work for both for size 1 & size 2, and
> > > use the switch-case to create the mask and and_value.
> > >
> > > You think that works enough?
> > Good, go ahead.
> >
> > >
> > > > It's very struggling to use macros to implement complex
> > > > functions.
> > >
> > > I agree, but with this we can achieve more generic code, which makes
> > > more clear what is the pattern for given function.
> > >
> > > > Could you consider a more relaxed optimization in which we could
> > > > insert inline cmpxchg/xchg_small?
> > >
> > > What about this: I finish the patches I have been working with
> > > (cmpxchg & xchg for sizes 1 and 2), and if they are fine we expand
> > > this patchset with them.  If not, I try relaxing them a little so we
> > > can merge with your set.
> > >
> > > Does that work for you?
> > Great, you could provide cmpxchg & xchg for sizes 1 and 2, then my
> > patch series would base on yours. After tested, I would give you
> > Tested-by.
>
> Awesome! Thanks!
>
> I will send it shortly, just compile-testing the kernel.
>

v3:
https://patchwork.kernel.org/project/linux-riscv/list/?series=3D772986&stat=
e=3D%2A&archive=3Dboth

> > >
> > > Best regards,
> > > Leo
> > >
> > >
> > > >
> > > > >
> > > > > 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 f=
or xchg
> > > > > https://lore.kernel.org/all/20230404163741.2762165-1-leobras@redh=
at.com/
> > > > >
> > > > > Changes since (cmpxchg) RFCv2:
> > > > > - Fixed  macros that depend on having a local variable with a mag=
ic name
> > > > > - Previous cast to (long) is now only applied on 4-bytes cmpxchg
> > > > > https://lore.kernel.org/all/20230321074249.2221674-1-leobras@redh=
at.com/
> > > > >
> > > > > Changes since (cmpxchg) RFCv1:
> > > > > - Fixed patch 4/6 suffix from 'w.aqrl' to '.w.aqrl', to avoid bui=
ld error
> > > > > https://lore.kernel.org/all/20230318080059.1109286-1-leobras@redh=
at.com/
> > > > >
> > > > >
> > > > > 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
> > > >
> > >
> >
> >
> > --
> > Best Regards
> >  Guo Ren
> >