Re: [PATCH] locking/atomics: Simplify the op definitions in atomic.h some more

[Andrea Parri]

On Sun, May 06, 2018 at 04:57:27PM +0200, Ingo Molnar wrote:
> 
> * Andrea Parri <andrea.parri@xxxxxxxxxxxxxxxxxxxx> wrote:
> 
> > Hi Ingo,
> > 
> > > From 5affbf7e91901143f84f1b2ca64f4afe70e210fd Mon Sep 17 00:00:00 2001
> > > From: Ingo Molnar <mingo@xxxxxxxxxx>
> > > Date: Sat, 5 May 2018 10:23:23 +0200
> > > Subject: [PATCH] locking/atomics: Simplify the op definitions in atomic.h some more
> > > 
> > > Before:
> > > 
> > >  #ifndef atomic_fetch_dec_relaxed
> > >  # ifndef atomic_fetch_dec
> > >  #  define atomic_fetch_dec(v)			atomic_fetch_sub(1, (v))
> > >  #  define atomic_fetch_dec_relaxed(v)		atomic_fetch_sub_relaxed(1, (v))
> > >  #  define atomic_fetch_dec_acquire(v)		atomic_fetch_sub_acquire(1, (v))
> > >  #  define atomic_fetch_dec_release(v)		atomic_fetch_sub_release(1, (v))
> > >  # else
> > >  #  define atomic_fetch_dec_relaxed		atomic_fetch_dec
> > >  #  define atomic_fetch_dec_acquire		atomic_fetch_dec
> > >  #  define atomic_fetch_dec_release		atomic_fetch_dec
> > >  # endif
> > >  #else
> > >  # ifndef atomic_fetch_dec_acquire
> > >  #  define atomic_fetch_dec_acquire(...)	__atomic_op_acquire(atomic_fetch_dec, __VA_ARGS__)
> > >  # endif
> > >  # ifndef atomic_fetch_dec_release
> > >  #  define atomic_fetch_dec_release(...)	__atomic_op_release(atomic_fetch_dec, __VA_ARGS__)
> > >  # endif
> > >  # ifndef atomic_fetch_dec
> > >  #  define atomic_fetch_dec(...)		__atomic_op_fence(atomic_fetch_dec, __VA_ARGS__)
> > >  # endif
> > >  #endif
> > > 
> > > After:
> > > 
> > >  #ifndef atomic_fetch_dec_relaxed
> > >  # ifndef atomic_fetch_dec
> > >  #  define atomic_fetch_dec(v)			atomic_fetch_sub(1, (v))
> > >  #  define atomic_fetch_dec_relaxed(v)		atomic_fetch_sub_relaxed(1, (v))
> > >  #  define atomic_fetch_dec_acquire(v)		atomic_fetch_sub_acquire(1, (v))
> > >  #  define atomic_fetch_dec_release(v)		atomic_fetch_sub_release(1, (v))
> > >  # else
> > >  #  define atomic_fetch_dec_relaxed		atomic_fetch_dec
> > >  #  define atomic_fetch_dec_acquire		atomic_fetch_dec
> > >  #  define atomic_fetch_dec_release		atomic_fetch_dec
> > >  # endif
> > >  #else
> > >  # ifndef atomic_fetch_dec
> > >  #  define atomic_fetch_dec(...)		__atomic_op_fence(atomic_fetch_dec, __VA_ARGS__)
> > >  #  define atomic_fetch_dec_acquire(...)	__atomic_op_acquire(atomic_fetch_dec, __VA_ARGS__)
> > >  #  define atomic_fetch_dec_release(...)	__atomic_op_release(atomic_fetch_dec, __VA_ARGS__)
> > >  # endif
> > >  #endif
> > > 
> > > The idea is that because we already group these APIs by certain defines
> > > such as atomic_fetch_dec_relaxed and atomic_fetch_dec in the primary
> > > branches - we can do the same in the secondary branch as well.
> > > 
> > > ( Also remove some unnecessarily duplicate comments, as the API
> > >   group defines are now pretty much self-documenting. )
> > > 
> > > No change in functionality.
> > > 
> > > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > > Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> > > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > > Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
> > > Cc: Will Deacon <will.deacon@xxxxxxx>
> > > Cc: linux-kernel@xxxxxxxxxxxxxxx
> > > Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
> > 
> > This breaks compilation on RISC-V. (For some of its atomics, the arch
> > currently defines the _relaxed and the full variants and it relies on
> > the generic definitions for the _acquire and the _release variants.)
> 
> I don't have cross-compilation for RISC-V, which is a relatively new arch.
> (Is there any RISC-V set of cross-compilation tools on kernel.org somewhere?)

I'm using the toolchain from:

  https://riscv.org/software-tools/

(adding Palmer and Albert in Cc:)


> 
> Could you please send a patch that defines those variants against Linus's tree, 
> like the PowerPC patch that does something similar:
> 
>   0476a632cb3a: locking/atomics/powerpc: Move cmpxchg helpers to asm/cmpxchg.h and define the full set of cmpxchg APIs
> 
> ?

Yes, please see below for a first RFC.

(BTW, get_maintainer.pl says that that patch missed Benjamin, Paul, Michael
 and linuxppc-dev@xxxxxxxxxxxxxxxx: FWIW, I'm Cc-ing the maintainers here.)

  Andrea