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Message-ID: <4d4dd1e8-042a-561a-4ffc-529638cb0780@csgroup.eu>
Date: Mon, 7 Aug 2023 16:13:41 +0000
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: Uros Bizjak <ubizjak@...il.com>,
"loongarch@...ts.linux.dev" <loongarch@...ts.linux.dev>,
"linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>,
"x86@...nel.org" <x86@...nel.org>,
"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC: Will Deacon <will@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Boqun Feng <boqun.feng@...il.com>,
Mark Rutland <mark.rutland@....com>,
Richard Henderson <richard.henderson@...aro.org>,
Ivan Kokshaysky <ink@...assic.park.msu.ru>,
Matt Turner <mattst88@...il.com>,
Huacai Chen <chenhuacai@...nel.org>,
WANG Xuerui <kernel@...0n.name>,
Jiaxun Yang <jiaxun.yang@...goat.com>,
Jun Yi <yijun@...ngson.cn>,
Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
Michael Ellerman <mpe@...erman.id.au>,
Nicholas Piggin <npiggin@...il.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>,
"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] locking/arch: Rewrite local_add_unless as static inline
function
Le 31/07/2023 à 10:42, Uros Bizjak a écrit :
> Rewrite local_add_unless as a static inline function with boolean
> return value, similar to arch_atomic_add_unless arch fallbacks.
>
> The function is currently unused.
Is it worth keeping the function if it is not used ?
Christophe
>
> Cc: Will Deacon <will@...nel.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Boqun Feng <boqun.feng@...il.com>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Richard Henderson <richard.henderson@...aro.org>
> Cc: Ivan Kokshaysky <ink@...assic.park.msu.ru>
> Cc: Matt Turner <mattst88@...il.com>
> Cc: Huacai Chen <chenhuacai@...nel.org>
> Cc: WANG Xuerui <kernel@...0n.name>
> Cc: Jiaxun Yang <jiaxun.yang@...goat.com>
> Cc: Jun Yi <yijun@...ngson.cn>
> Cc: Thomas Bogendoerfer <tsbogend@...ha.franken.de>
> Cc: Michael Ellerman <mpe@...erman.id.au>
> Cc: Nicholas Piggin <npiggin@...il.com>
> Cc: Christophe Leroy <christophe.leroy@...roup.eu>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Signed-off-by: Uros Bizjak <ubizjak@...il.com>
> ---
> arch/alpha/include/asm/local.h | 33 +++++++++++++++---------------
> arch/loongarch/include/asm/local.h | 27 ++++++++++++++----------
> arch/mips/include/asm/local.h | 27 ++++++++++++++----------
> arch/powerpc/include/asm/local.h | 12 +++++------
> arch/x86/include/asm/local.h | 33 +++++++++++++++---------------
> 5 files changed, 70 insertions(+), 62 deletions(-)
>
> diff --git a/arch/alpha/include/asm/local.h b/arch/alpha/include/asm/local.h
> index 0fcaad642cc3..88eb398947a5 100644
> --- a/arch/alpha/include/asm/local.h
> +++ b/arch/alpha/include/asm/local.h
> @@ -65,28 +65,27 @@ static __inline__ bool local_try_cmpxchg(local_t *l, long *old, long new)
> #define local_xchg(l, n) (xchg_local(&((l)->a.counter), (n)))
>
> /**
> - * local_add_unless - add unless the number is a given value
> + * local_add_unless - add unless the number is already a given value
> * @l: pointer of type local_t
> * @a: the amount to add to l...
> * @u: ...unless l is equal to u.
> *
> - * Atomically adds @a to @l, so long as it was not @u.
> - * Returns non-zero if @l was not @u, and zero otherwise.
> + * Atomically adds @a to @l, if @v was not already @u.
> + * Returns true if the addition was done.
> */
> -#define local_add_unless(l, a, u) \
> -({ \
> - long c, old; \
> - c = local_read(l); \
> - for (;;) { \
> - if (unlikely(c == (u))) \
> - break; \
> - old = local_cmpxchg((l), c, c + (a)); \
> - if (likely(old == c)) \
> - break; \
> - c = old; \
> - } \
> - c != (u); \
> -})
> +static __inline__ bool
> +local_add_unless(local_t *l, long a, long u)
> +{
> + long c = local_read(l);
> +
> + do {
> + if (unlikely(c == u))
> + return false;
> + } while (!local_try_cmpxchg(l, &c, c + a));
> +
> + return true;
> +}
> +
> #define local_inc_not_zero(l) local_add_unless((l), 1, 0)
>
> #define local_add_negative(a, l) (local_add_return((a), (l)) < 0)
> diff --git a/arch/loongarch/include/asm/local.h b/arch/loongarch/include/asm/local.h
> index 83e995b30e47..15bc3579f16c 100644
> --- a/arch/loongarch/include/asm/local.h
> +++ b/arch/loongarch/include/asm/local.h
> @@ -70,22 +70,27 @@ static inline bool local_try_cmpxchg(local_t *l, long *old, long new)
> #define local_xchg(l, n) (atomic_long_xchg((&(l)->a), (n)))
>
> /**
> - * local_add_unless - add unless the number is a given value
> + * local_add_unless - add unless the number is already a given value
> * @l: pointer of type local_t
> * @a: the amount to add to l...
> * @u: ...unless l is equal to u.
> *
> - * Atomically adds @a to @l, so long as it was not @u.
> - * Returns non-zero if @l was not @u, and zero otherwise.
> + * Atomically adds @a to @l, if @v was not already @u.
> + * Returns true if the addition was done.
> */
> -#define local_add_unless(l, a, u) \
> -({ \
> - long c, old; \
> - c = local_read(l); \
> - while (c != (u) && (old = local_cmpxchg((l), c, c + (a))) != c) \
> - c = old; \
> - c != (u); \
> -})
> +static inline bool
> +local_add_unless(local_t *l, long a, long u)
> +{
> + long c = local_read(l);
> +
> + do {
> + if (unlikely(c == u))
> + return false;
> + } while (!local_try_cmpxchg(l, &c, c + a));
> +
> + return true;
> +}
> +
> #define local_inc_not_zero(l) local_add_unless((l), 1, 0)
>
> #define local_dec_return(l) local_sub_return(1, (l))
> diff --git a/arch/mips/include/asm/local.h b/arch/mips/include/asm/local.h
> index 5daf6fe8e3e9..90435158a083 100644
> --- a/arch/mips/include/asm/local.h
> +++ b/arch/mips/include/asm/local.h
> @@ -108,22 +108,27 @@ static __inline__ bool local_try_cmpxchg(local_t *l, long *old, long new)
> #define local_xchg(l, n) (atomic_long_xchg((&(l)->a), (n)))
>
> /**
> - * local_add_unless - add unless the number is a given value
> + * local_add_unless - add unless the number is already a given value
> * @l: pointer of type local_t
> * @a: the amount to add to l...
> * @u: ...unless l is equal to u.
> *
> - * Atomically adds @a to @l, so long as it was not @u.
> - * Returns non-zero if @l was not @u, and zero otherwise.
> + * Atomically adds @a to @l, if @v was not already @u.
> + * Returns true if the addition was done.
> */
> -#define local_add_unless(l, a, u) \
> -({ \
> - long c, old; \
> - c = local_read(l); \
> - while (c != (u) && (old = local_cmpxchg((l), c, c + (a))) != c) \
> - c = old; \
> - c != (u); \
> -})
> +static __inline__ bool
> +local_add_unless(local_t *l, long a, long u)
> +{
> + long c = local_read(l);
> +
> + do {
> + if (unlikely(c == u))
> + return false;
> + } while (!local_try_cmpxchg(l, &c, c + a));
> +
> + return true;
> +}
> +
> #define local_inc_not_zero(l) local_add_unless((l), 1, 0)
>
> #define local_dec_return(l) local_sub_return(1, (l))
> diff --git a/arch/powerpc/include/asm/local.h b/arch/powerpc/include/asm/local.h
> index 45492fb5bf22..ec6ced6d7ced 100644
> --- a/arch/powerpc/include/asm/local.h
> +++ b/arch/powerpc/include/asm/local.h
> @@ -115,23 +115,23 @@ static __inline__ long local_xchg(local_t *l, long n)
> }
>
> /**
> - * local_add_unless - add unless the number is a given value
> + * local_add_unless - add unless the number is already a given value
> * @l: pointer of type local_t
> * @a: the amount to add to v...
> * @u: ...unless v is equal to u.
> *
> - * Atomically adds @a to @l, so long as it was not @u.
> - * Returns non-zero if @l was not @u, and zero otherwise.
> + * Atomically adds @a to @l, if @v was not already @u.
> + * Returns true if the addition was done.
> */
> -static __inline__ int local_add_unless(local_t *l, long a, long u)
> +static __inline__ bool local_add_unless(local_t *l, long a, long u)
> {
> unsigned long flags;
> - int ret = 0;
> + bool ret = false;
>
> powerpc_local_irq_pmu_save(flags);
> if (l->v != u) {
> l->v += a;
> - ret = 1;
> + ret = true;
> }
> powerpc_local_irq_pmu_restore(flags);
>
> diff --git a/arch/x86/include/asm/local.h b/arch/x86/include/asm/local.h
> index 56d4ef604b91..46ce92d4e556 100644
> --- a/arch/x86/include/asm/local.h
> +++ b/arch/x86/include/asm/local.h
> @@ -135,28 +135,27 @@ static inline bool local_try_cmpxchg(local_t *l, long *old, long new)
> #define local_xchg(l, n) (xchg(&((l)->a.counter), (n)))
>
> /**
> - * local_add_unless - add unless the number is a given value
> + * local_add_unless - add unless the number is already a given value
> * @l: pointer of type local_t
> * @a: the amount to add to l...
> * @u: ...unless l is equal to u.
> *
> - * Atomically adds @a to @l, so long as it was not @u.
> - * Returns non-zero if @l was not @u, and zero otherwise.
> + * Atomically adds @a to @l, if @v was not already @u.
> + * Returns true if the addition was done.
> */
> -#define local_add_unless(l, a, u) \
> -({ \
> - long c, old; \
> - c = local_read((l)); \
> - for (;;) { \
> - if (unlikely(c == (u))) \
> - break; \
> - old = local_cmpxchg((l), c, c + (a)); \
> - if (likely(old == c)) \
> - break; \
> - c = old; \
> - } \
> - c != (u); \
> -})
> +static __always_inline bool
> +local_add_unless(local_t *l, long a, long u)
> +{
> + long c = local_read(l);
> +
> + do {
> + if (unlikely(c == u))
> + return false;
> + } while (!local_try_cmpxchg(l, &c, c + a));
> +
> + return true;
> +}
> +
> #define local_inc_not_zero(l) local_add_unless((l), 1, 0)
>
> /* On x86_32, these are no better than the atomic variants.
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