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Message-ID: <d13fd45583d57080e4b81eeac55b787378cbcfa2.camel@xry111.site>
Date: Fri, 06 Sep 2024 16:02:02 +0800
From: Xi Ruoyao <xry111@...111.site>
To: Uros Bizjak <ubizjak@...il.com>, loongarch@...ts.linux.dev,
linux-kernel@...r.kernel.org
Cc: Huacai Chen <chenhuacai@...nel.org>, WANG Xuerui <kernel@...0n.name>,
Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v4] LoongArch/percpu: Simplify _percpu_read() and
_percpu_write()
On Fri, 2024-09-06 at 08:57 +0200, Uros Bizjak wrote:
> _percpu_read() and _percpu_write() macros call __percpu_read()
> and __percpu_write() static inline functions that result in a single
> assembly instruction. Percpu infrastructure expects its leaf
> definitions to encode the size of their percpu variable, so the patch
> merges asm clauses from the static inline function into the
> corresponding leaf macros.
>
> The secondary effect of this change is to avoid explicit __percpu
> function arguments. Currently, __percpu macro is defined in
> include/linux/compiler_types.h, but with proposed patch [1],
> __percpu definition will need macros from include/asm-generic/percpu.h,
> creating forward dependency loop.
>
> The proposed solution is the same as x86 architecture uses.
>
> Patch is compile tested only.
Boots fine and per-CPU variable seems working fine (tried with a kernel
module defining a per-CPU variable and operating on it).
Tested-by: Xi Ruoyao <xry111@...111.site>
>
> [1] https://lore.kernel.org/lkml/20240812115945.484051-4-ubizjak@gmail.com/
>
> Signed-off-by: Uros Bizjak <ubizjak@...il.com>
> Cc: Huacai Chen <chenhuacai@...nel.org>
> Cc: WANG Xuerui <kernel@...0n.name>
> Cc: Xi Ruoyao <xry111@...111.site>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> ---
> v2: Add a missing cast and a missing coma in the asm template,
> reported by kernel test robot. Some formatting changes.
> v3: Check the type of _val in _percpu_write().
> v4: Remove type ckecking of _val. Remove unnecessary zero-extensions
> and truncations.
> ---
> arch/loongarch/include/asm/percpu.h | 124 ++++++++--------------------
> 1 file changed, 35 insertions(+), 89 deletions(-)
>
> diff --git a/arch/loongarch/include/asm/percpu.h b/arch/loongarch/include/asm/percpu.h
> index 8f290e5546cf..87be9b14e9da 100644
> --- a/arch/loongarch/include/asm/percpu.h
> +++ b/arch/loongarch/include/asm/percpu.h
> @@ -68,75 +68,6 @@ PERCPU_OP(and, and, &)
> PERCPU_OP(or, or, |)
> #undef PERCPU_OP
>
> -static __always_inline unsigned long __percpu_read(void __percpu *ptr, int size)
> -{
> - unsigned long ret;
> -
> - switch (size) {
> - case 1:
> - __asm__ __volatile__ ("ldx.b %[ret], $r21, %[ptr] \n"
> - : [ret] "=&r"(ret)
> - : [ptr] "r"(ptr)
> - : "memory");
> - break;
> - case 2:
> - __asm__ __volatile__ ("ldx.h %[ret], $r21, %[ptr] \n"
> - : [ret] "=&r"(ret)
> - : [ptr] "r"(ptr)
> - : "memory");
> - break;
> - case 4:
> - __asm__ __volatile__ ("ldx.w %[ret], $r21, %[ptr] \n"
> - : [ret] "=&r"(ret)
> - : [ptr] "r"(ptr)
> - : "memory");
> - break;
> - case 8:
> - __asm__ __volatile__ ("ldx.d %[ret], $r21, %[ptr] \n"
> - : [ret] "=&r"(ret)
> - : [ptr] "r"(ptr)
> - : "memory");
> - break;
> - default:
> - ret = 0;
> - BUILD_BUG();
> - }
> -
> - return ret;
> -}
> -
> -static __always_inline void __percpu_write(void __percpu *ptr, unsigned long val, int size)
> -{
> - switch (size) {
> - case 1:
> - __asm__ __volatile__("stx.b %[val], $r21, %[ptr] \n"
> - :
> - : [val] "r" (val), [ptr] "r" (ptr)
> - : "memory");
> - break;
> - case 2:
> - __asm__ __volatile__("stx.h %[val], $r21, %[ptr] \n"
> - :
> - : [val] "r" (val), [ptr] "r" (ptr)
> - : "memory");
> - break;
> - case 4:
> - __asm__ __volatile__("stx.w %[val], $r21, %[ptr] \n"
> - :
> - : [val] "r" (val), [ptr] "r" (ptr)
> - : "memory");
> - break;
> - case 8:
> - __asm__ __volatile__("stx.d %[val], $r21, %[ptr] \n"
> - :
> - : [val] "r" (val), [ptr] "r" (ptr)
> - : "memory");
> - break;
> - default:
> - BUILD_BUG();
> - }
> -}
> -
> static __always_inline unsigned long __percpu_xchg(void *ptr, unsigned long val, int size)
> {
> switch (size) {
> @@ -157,6 +88,33 @@ static __always_inline unsigned long __percpu_xchg(void *ptr, unsigned long val,
> return 0;
> }
>
> +#define __pcpu_op_1(op) op ".b "
> +#define __pcpu_op_2(op) op ".h "
> +#define __pcpu_op_4(op) op ".w "
> +#define __pcpu_op_8(op) op ".d "
> +
> +#define _percpu_read(size, _pcp) \
> +({ \
> + typeof(_pcp) __pcp_ret; \
> + \
> + __asm__ __volatile__( \
> + __pcpu_op_##size("ldx") "%[ret], $r21, %[ptr] \n" \
> + : [ret] "=&r"(__pcp_ret) \
> + : [ptr] "r"(&(_pcp)) \
> + : "memory"); \
> + \
> + __pcp_ret; \
> +})
> +
> +#define _percpu_write(size, _pcp, _val) \
> +do { \
> + __asm__ __volatile__( \
> + __pcpu_op_##size("stx") "%[val], $r21, %[ptr] \n" \
> + : \
> + : [val] "r"(_val), [ptr] "r"(&(_pcp)) \
> + : "memory"); \
> +} while (0)
> +
> /* this_cpu_cmpxchg */
> #define _protect_cmpxchg_local(pcp, o, n) \
> ({ \
> @@ -167,18 +125,6 @@ static __always_inline unsigned long __percpu_xchg(void *ptr, unsigned long val,
> __ret; \
> })
>
> -#define _percpu_read(pcp) \
> -({ \
> - typeof(pcp) __retval; \
> - __retval = (typeof(pcp))__percpu_read(&(pcp), sizeof(pcp)); \
> - __retval; \
> -})
> -
> -#define _percpu_write(pcp, val) \
> -do { \
> - __percpu_write(&(pcp), (unsigned long)(val), sizeof(pcp)); \
> -} while (0) \
> -
> #define _pcp_protect(operation, pcp, val) \
> ({ \
> typeof(pcp) __retval; \
> @@ -215,15 +161,15 @@ do { \
> #define this_cpu_or_4(pcp, val) _percpu_or(pcp, val)
> #define this_cpu_or_8(pcp, val) _percpu_or(pcp, val)
>
> -#define this_cpu_read_1(pcp) _percpu_read(pcp)
> -#define this_cpu_read_2(pcp) _percpu_read(pcp)
> -#define this_cpu_read_4(pcp) _percpu_read(pcp)
> -#define this_cpu_read_8(pcp) _percpu_read(pcp)
> +#define this_cpu_read_1(pcp) _percpu_read(1, pcp)
> +#define this_cpu_read_2(pcp) _percpu_read(2, pcp)
> +#define this_cpu_read_4(pcp) _percpu_read(4, pcp)
> +#define this_cpu_read_8(pcp) _percpu_read(8, pcp)
>
> -#define this_cpu_write_1(pcp, val) _percpu_write(pcp, val)
> -#define this_cpu_write_2(pcp, val) _percpu_write(pcp, val)
> -#define this_cpu_write_4(pcp, val) _percpu_write(pcp, val)
> -#define this_cpu_write_8(pcp, val) _percpu_write(pcp, val)
> +#define this_cpu_write_1(pcp, val) _percpu_write(1, pcp, val)
> +#define this_cpu_write_2(pcp, val) _percpu_write(2, pcp, val)
> +#define this_cpu_write_4(pcp, val) _percpu_write(4, pcp, val)
> +#define this_cpu_write_8(pcp, val) _percpu_write(8, pcp, val)
>
> #define this_cpu_xchg_1(pcp, val) _percpu_xchg(pcp, val)
> #define this_cpu_xchg_2(pcp, val) _percpu_xchg(pcp, val)
--
Xi Ruoyao <xry111@...111.site>
School of Aerospace Science and Technology, Xidian University
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