linux-kernel - Re: [PATCH 13/13] atomics/treewide: make test ops optional

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Date:   Tue, 29 May 2018 10:57:40 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     linux-kernel@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>
Cc:     Boqun Feng <boqun.feng@...il.com>,
        Will Deacon <will.deacon@....com>
Subject: Re: [PATCH 13/13] atomics/treewide: make test ops optional

On Tue, May 29, 2018 at 10:11:19AM +0100, Mark Rutland wrote:
> On Wed, May 23, 2018 at 02:35:33PM +0100, Mark Rutland wrote:
> > Some of the atomics return the result of a test applied after the atomic
> > operation, and almost all architectures implement these as trivial
> > wrappers around the underlying atomic. Specifically:
> > 
> > * <atomic>_inc_and_test(v) is (<atomic>_inc_return(v) == 0)
> > 
> > * <atomic>_dec_and_test(v) is (<atomic>_dec_return(v) == 0)
> > 
> > * <atomic>_sub_and_test(i, v) is (<atomic>_sub_return(i, v) == 0)
> > 
> > * <atomic>_add_negative(i, v) is (<atomic>_add_return(i, v) < 0)
> > 
> > Rather than have these definitions duplicated in all architectures, with
> > minor inconsistencies in formatting and documentation, let's make these
> > operations optional, with default fallbacks as above. Implementations
> > must now provide a preprocessor symbol.
> > 
> > The instrumented atomics are updated accordingly.
> > 
> > Both x86 and m68k have custom implementations, which are left as-is,
> > given preprocessor symbols to avoid being overridden.
> > 
> > There should be no functional change as a result of this patch.
> > 
> > Signed-off-by: Mark Rutland <mark.rutland@....com>
> > Cc: Boqun Feng <boqun.feng@...il.com>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Cc: Will Deacon <will.deacon@....com>
> > ---
> >  arch/alpha/include/asm/atomic.h           |  12 ---
> >  arch/arc/include/asm/atomic.h             |  10 ---
> >  arch/arm/include/asm/atomic.h             |   9 ---
> >  arch/arm64/include/asm/atomic.h           |   8 --
> >  arch/h8300/include/asm/atomic.h           |   5 --
> >  arch/hexagon/include/asm/atomic.h         |   5 --
> >  arch/ia64/include/asm/atomic.h            |  23 ------
> >  arch/m68k/include/asm/atomic.h            |   4 +
> >  arch/mips/include/asm/atomic.h            |  84 --------------------
> >  arch/parisc/include/asm/atomic.h          |  22 ------
> >  arch/powerpc/include/asm/atomic.h         |  30 --------
> >  arch/s390/include/asm/atomic.h            |   8 --
> >  arch/sh/include/asm/atomic.h              |   4 -
> >  arch/sparc/include/asm/atomic_32.h        |  15 ----
> >  arch/sparc/include/asm/atomic_64.h        |  20 -----
> >  arch/x86/include/asm/atomic.h             |   4 +
> >  arch/x86/include/asm/atomic64_32.h        |  54 -------------
> >  arch/x86/include/asm/atomic64_64.h        |   4 +
> >  arch/xtensa/include/asm/atomic.h          |  42 ----------
> >  include/asm-generic/atomic-instrumented.h |  24 ++++++
> >  include/asm-generic/atomic.h              |   9 ---
> >  include/asm-generic/atomic64.h            |   4 -
> >  include/linux/atomic.h                    | 124 ++++++++++++++++++++++++++++++
> >  23 files changed, 160 insertions(+), 364 deletions(-)
> 
> I missed the risvc bits, since those are generated and don't have
> preprocessor symbols.

Ugh, I missed a guard for inc_not_zero on x86_32 in an earlier patch,
too.

I'll spin a v2 of the series.

Mark.