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References: <20200517152916.3146539-1-brgerst@gmail.com> <20200517152916.3146539-4-brgerst@gmail.com>
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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Mon, 18 May 2020 14:27:23 -0700
Message-ID: <CAKwvOdk7dTndpMaVmEH874zfzLSK3DGGmfaEvaza=g6OwhX61g@mail.gmail.com>
Subject: Re: [PATCH 3/7] x86/percpu: Clean up percpu_from_op()
To:     Brian Gerst <brgerst@gmail.com>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@kernel.org>, Borislav Petkov <bp@alien8.de>,
        "H . Peter Anvin" <hpa@zytor.com>,
        Andy Lutomirski <luto@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>
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On Sun, May 17, 2020 at 8:29 AM Brian Gerst <brgerst@gmail.com> wrote:
>
> The core percpu macros already have a switch on the data size, so the switch
> in the x86 code is redundant and produces more dead code.
>
> Also use appropriate types for the width of the instructions.  This avoids
> errors when compiling with Clang.
>
> Signed-off-by: Brian Gerst <brgerst@gmail.com>

Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

> ---
>  arch/x86/include/asm/percpu.h | 50 +++++++++++------------------------
>  1 file changed, 15 insertions(+), 35 deletions(-)
>
> diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h
> index 233c7a78d1a6..93f33202492d 100644
> --- a/arch/x86/include/asm/percpu.h
> +++ b/arch/x86/include/asm/percpu.h
> @@ -190,33 +190,13 @@ do {                                                                      \
>         }                                                               \
>  } while (0)
>
> -#define percpu_from_op(qual, op, var)                  \
> -({                                                     \
> -       typeof(var) pfo_ret__;                          \
> -       switch (sizeof(var)) {                          \
> -       case 1:                                         \
> -               asm qual (op "b "__percpu_arg(1)",%0"   \
> -                   : "=q" (pfo_ret__)                  \
> -                   : "m" (var));                       \
> -               break;                                  \
> -       case 2:                                         \
> -               asm qual (op "w "__percpu_arg(1)",%0"   \
> -                   : "=r" (pfo_ret__)                  \
> -                   : "m" (var));                       \
> -               break;                                  \
> -       case 4:                                         \
> -               asm qual (op "l "__percpu_arg(1)",%0"   \
> -                   : "=r" (pfo_ret__)                  \
> -                   : "m" (var));                       \
> -               break;                                  \
> -       case 8:                                         \
> -               asm qual (op "q "__percpu_arg(1)",%0"   \
> -                   : "=r" (pfo_ret__)                  \
> -                   : "m" (var));                       \
> -               break;                                  \
> -       default: __bad_percpu_size();                   \
> -       }                                               \
> -       pfo_ret__;                                      \
> +#define percpu_from_op(size, qual, op, _var)                           \
> +({                                                                     \
> +       __pcpu_type_##size pfo_val__;                                   \
> +       asm qual (__pcpu_op2_##size(op, __percpu_arg([var]), "%[val]")  \
> +           : [val] __pcpu_reg_##size("=", pfo_val__)                   \
> +           : [var] "m" (_var));                                        \
> +       (typeof(_var))(unsigned long) pfo_val__;                        \
>  })
>
>  #define percpu_stable_op(op, var)                      \
> @@ -401,9 +381,9 @@ do {                                                                        \
>   */
>  #define this_cpu_read_stable(var)      percpu_stable_op("mov", var)
>
> -#define raw_cpu_read_1(pcp)            percpu_from_op(, "mov", pcp)
> -#define raw_cpu_read_2(pcp)            percpu_from_op(, "mov", pcp)
> -#define raw_cpu_read_4(pcp)            percpu_from_op(, "mov", pcp)
> +#define raw_cpu_read_1(pcp)            percpu_from_op(1, , "mov", pcp)
> +#define raw_cpu_read_2(pcp)            percpu_from_op(2, , "mov", pcp)
> +#define raw_cpu_read_4(pcp)            percpu_from_op(4, , "mov", pcp)
>
>  #define raw_cpu_write_1(pcp, val)      percpu_to_op(1, , "mov", (pcp), val)
>  #define raw_cpu_write_2(pcp, val)      percpu_to_op(2, , "mov", (pcp), val)
> @@ -433,9 +413,9 @@ do {                                                                        \
>  #define raw_cpu_xchg_2(pcp, val)       raw_percpu_xchg_op(pcp, val)
>  #define raw_cpu_xchg_4(pcp, val)       raw_percpu_xchg_op(pcp, val)
>
> -#define this_cpu_read_1(pcp)           percpu_from_op(volatile, "mov", pcp)
> -#define this_cpu_read_2(pcp)           percpu_from_op(volatile, "mov", pcp)
> -#define this_cpu_read_4(pcp)           percpu_from_op(volatile, "mov", pcp)
> +#define this_cpu_read_1(pcp)           percpu_from_op(1, volatile, "mov", pcp)
> +#define this_cpu_read_2(pcp)           percpu_from_op(2, volatile, "mov", pcp)
> +#define this_cpu_read_4(pcp)           percpu_from_op(4, volatile, "mov", pcp)
>  #define this_cpu_write_1(pcp, val)     percpu_to_op(1, volatile, "mov", (pcp), val)
>  #define this_cpu_write_2(pcp, val)     percpu_to_op(2, volatile, "mov", (pcp), val)
>  #define this_cpu_write_4(pcp, val)     percpu_to_op(4, volatile, "mov", (pcp), val)
> @@ -488,7 +468,7 @@ do {                                                                        \
>   * 32 bit must fall back to generic operations.
>   */
>  #ifdef CONFIG_X86_64
> -#define raw_cpu_read_8(pcp)                    percpu_from_op(, "mov", pcp)
> +#define raw_cpu_read_8(pcp)                    percpu_from_op(8, , "mov", pcp)
>  #define raw_cpu_write_8(pcp, val)              percpu_to_op(8, , "mov", (pcp), val)
>  #define raw_cpu_add_8(pcp, val)                        percpu_add_op(, (pcp), val)
>  #define raw_cpu_and_8(pcp, val)                        percpu_to_op(8, , "and", (pcp), val)
> @@ -497,7 +477,7 @@ do {                                                                        \
>  #define raw_cpu_xchg_8(pcp, nval)              raw_percpu_xchg_op(pcp, nval)
>  #define raw_cpu_cmpxchg_8(pcp, oval, nval)     percpu_cmpxchg_op(, pcp, oval, nval)
>
> -#define this_cpu_read_8(pcp)                   percpu_from_op(volatile, "mov", pcp)
> +#define this_cpu_read_8(pcp)                   percpu_from_op(8, volatile, "mov", pcp)
>  #define this_cpu_write_8(pcp, val)             percpu_to_op(8, volatile, "mov", (pcp), val)
>  #define this_cpu_add_8(pcp, val)               percpu_add_op(volatile, (pcp), val)
>  #define this_cpu_and_8(pcp, val)               percpu_to_op(8, volatile, "and", (pcp), val)
> --
> 2.25.4
>


-- 
Thanks,
~Nick Desaulniers