linux-kernel - Re: [tip:locking/core] locking/atomics: Simplify the op definitions in atomic.h some more

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Message-ID: <20180515085417.GB30420@gmail.com>
Date:   Tue, 15 May 2018 10:54:17 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Will Deacon <will.deacon@....com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
        mark.rutland@....com, torvalds@...ux-foundation.org,
        paulmck@...ux.vnet.ibm.com, tglx@...utronix.de, hpa@...or.com,
        linux-tip-commits@...r.kernel.org
Subject: Re: [tip:locking/core] locking/atomics: Simplify the op definitions
 in atomic.h some more


* Will Deacon <will.deacon@....com> wrote:

> With this patch, we're already seeing arch code (powerpc, risc-v) having
> to add what is basically boiler-plate code, and it seems like we're just
> doing this to make the generic code more readable! I'd much prefer we kept
> the arch code simple, and took on the complexity burden in the generic code
> where it can be looked after in one place.

For PowerPC this is not really true, the patch has this effect:

   2 files changed, 28 insertions(+), 20 deletions(-)

and made it more obvious where the arch gets its low level definitions from.

For RISC-V it's true:

 arch/riscv/include/asm/atomic.h | 44 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)

but even before this it was already largely boilerplate:

#define atomic_inc_return_relaxed	atomic_inc_return_relaxed
#define atomic_dec_return_relaxed	atomic_dec_return_relaxed
#define atomic_inc_return		atomic_inc_return
#define atomic_dec_return		atomic_dec_return

#define atomic_fetch_inc_relaxed	atomic_fetch_inc_relaxed
#define atomic_fetch_dec_relaxed	atomic_fetch_dec_relaxed
#define atomic_fetch_inc		atomic_fetch_inc
#define atomic_fetch_dec		atomic_fetch_dec

#ifndef CONFIG_GENERIC_ATOMIC64
#define atomic64_inc_return_relaxed	atomic64_inc_return_relaxed
#define atomic64_dec_return_relaxed	atomic64_dec_return_relaxed
#define atomic64_inc_return		atomic64_inc_return
#define atomic64_dec_return		atomic64_dec_return

#define atomic64_fetch_inc_relaxed	atomic64_fetch_inc_relaxed
#define atomic64_fetch_dec_relaxed	atomic64_fetch_dec_relaxed
#define atomic64_fetch_inc		atomic64_fetch_inc
#define atomic64_fetch_dec		atomic64_fetch_dec
#endif

What this change does it that it makes _all_ the low level ops obviously mapped in 
the low level header, if an arch decides to implement the _relaxed variants 
itself. Not half of them in the low level header, half of them in the generic 
header...

Thanks,

	Ingo