On Sat, May 30, 2020 at 3:11 PM Brian Gerst <brge...@gmail.com> wrote:
>
> Use __pcpu_size_call_return() to simplify this_cpu_read_stable().
Clever! As in this_cpu_read() in include/linux/percpu-defs.h. Could
be its own patch before this, but it's fine.
Reviewed-by: Nick Desaulniers <ndesaulni...@google.com>
> Also remove __bad_percpu_size() which is now unused.
>
> Signed-off-by: Brian Gerst <brge...@gmail.com>
> ---
> arch/x86/include/asm/percpu.h | 41 ++++++++++-------------------------
> 1 file changed, 12 insertions(+), 29 deletions(-)
>
> diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h
> index 7efc0b5c4ff0..cf2b9c2a241e 100644
> --- a/arch/x86/include/asm/percpu.h
> +++ b/arch/x86/include/asm/percpu.h
> @@ -85,7 +85,6 @@
>
> /* For arch-specific code, we can use direct single-insn ops (they
> * don't give an lvalue though). */
> -extern void __bad_percpu_size(void);
>
> #define __pcpu_type_1 u8
> #define __pcpu_type_2 u16
> @@ -167,33 +166,13 @@ do {
> \
> (typeof(_var))(unsigned long) pfo_val__; \
> })
>
> -#define percpu_stable_op(op, var) \
> -({ \
> - typeof(var) pfo_ret__; \
> - switch (sizeof(var)) { \
> - case 1: \
> - asm(op "b "__percpu_arg(P1)",%0" \
What does the `P` do here?
https://gcc.gnu.org/onlinedocs/gcc/Simple-Constraints.html#Simple-Constraints
says can be machine dependent integral literal in a certain range.
https://gcc.gnu.org/onlinedocs/gcc/Machine-Constraints.html#Machine-Constraints
doesn't document `P` for x86 though...
> - : "=q" (pfo_ret__) \
> - : "p" (&(var))); \
> - break; \
> - case 2: \
> - asm(op "w "__percpu_arg(P1)",%0" \
> - : "=r" (pfo_ret__) \
> - : "p" (&(var))); \
> - break; \
> - case 4: \
> - asm(op "l "__percpu_arg(P1)",%0" \
> - : "=r" (pfo_ret__) \
> - : "p" (&(var))); \
> - break; \
> - case 8: \
> - asm(op "q "__percpu_arg(P1)",%0" \
> - : "=r" (pfo_ret__) \
> - : "p" (&(var))); \
> - break; \
> - default: __bad_percpu_size(); \
> - } \
> - pfo_ret__; \
> +#define percpu_stable_op(size, op, _var) \
> +({ \
> + __pcpu_type_##size pfo_val__; \
> + asm(__pcpu_op2_##size(op, __percpu_arg(P[var]), "%[val]") \
> + : [val] __pcpu_reg_##size("=", pfo_val__) \
> + : [var] "p" (&(_var))); \
> + (typeof(_var))(unsigned long) pfo_val__; \
> })
>
> /*
> @@ -258,7 +237,11 @@ do {
> \
> * per-thread variables implemented as per-cpu variables and thus
> * stable for the duration of the respective task.
> */
> -#define this_cpu_read_stable(var) percpu_stable_op("mov", var)
> +#define this_cpu_read_stable_1(pcp) percpu_stable_op(1, "mov", pcp)
> +#define this_cpu_read_stable_2(pcp) percpu_stable_op(2, "mov", pcp)
> +#define this_cpu_read_stable_4(pcp) percpu_stable_op(4, "mov", pcp)
> +#define this_cpu_read_stable_8(pcp) percpu_stable_op(8, "mov", pcp)
> +#define this_cpu_read_stable(pcp)
> __pcpu_size_call_return(this_cpu_read_stable_, 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)
> --
> 2.25.4
>
--
Thanks,
~Nick Desaulniers
