Re: [PATCH] locking/arch: Rewrite local_add_unless as static inline function

[Christophe Leroy]

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@xxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Boqun Feng <boqun.feng@xxxxxxxxx>
> Cc: Mark Rutland <mark.rutland@xxxxxxx>
> Cc: Richard Henderson <richard.henderson@xxxxxxxxxx>
> Cc: Ivan Kokshaysky <ink@xxxxxxxxxxxxxxxxxxxx>
> Cc: Matt Turner <mattst88@xxxxxxxxx>
> Cc: Huacai Chen <chenhuacai@xxxxxxxxxx>
> Cc: WANG Xuerui <kernel@xxxxxxxxxx>
> Cc: Jiaxun Yang <jiaxun.yang@xxxxxxxxxxx>
> Cc: Jun Yi <yijun@xxxxxxxxxxx>
> Cc: Thomas Bogendoerfer <tsbogend@xxxxxxxxxxxxxxxx>
> Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> Cc: Nicholas Piggin <npiggin@xxxxxxxxx>
> Cc: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxxxx>
> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> Signed-off-by: Uros Bizjak <ubizjak@xxxxxxxxx>
> ---
>   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.