Re: [PATCH 4/7] x86/percpu: Clean up percpu_add_op()
From: Nick Desaulniers
Date: Mon May 18 2020 - 19:43:18 EST
On Sun, May 17, 2020 at 8:29 AM Brian Gerst <brgerst@xxxxxxxxx> 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@xxxxxxxxx>
> ---
> arch/x86/include/asm/percpu.h | 99 ++++++++---------------------------
> 1 file changed, 22 insertions(+), 77 deletions(-)
>
> diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h
> index 93f33202492d..21c5013a681a 100644
> --- a/arch/x86/include/asm/percpu.h
> +++ b/arch/x86/include/asm/percpu.h
> @@ -130,64 +130,32 @@ do { \
> : [val] __pcpu_reg_imm_##size(pto_val__)); \
> } while (0)
>
> +#define percpu_unary_op(size, qual, op, _var) \
> +({ \
> + asm qual (__pcpu_op1_##size(op, __percpu_arg([var])) \
> + : [var] "+m" (_var)); \
> +})
> +
> /*
> * Generate a percpu add to memory instruction and optimize code
> * if one is added or subtracted.
> */
> -#define percpu_add_op(qual, var, val) \
> +#define percpu_add_op(size, qual, var, val) \
> do { \
> - typedef typeof(var) pao_T__; \
> const int pao_ID__ = (__builtin_constant_p(val) && \
> ((val) == 1 || (val) == -1)) ? \
> (int)(val) : 0; \
> if (0) { \
> - pao_T__ pao_tmp__; \
> + typeof(var) pao_tmp__; \
> pao_tmp__ = (val); \
> (void)pao_tmp__; \
> } \
Prefer __same_type() from include/linux/compiler_types.h here as well.
Nice elimination of the typedef.
> - switch (sizeof(var)) { \
> - case 1: \
> - if (pao_ID__ == 1) \
> - asm qual ("incb "__percpu_arg(0) : "+m" (var)); \
> - else if (pao_ID__ == -1) \
> - asm qual ("decb "__percpu_arg(0) : "+m" (var)); \
> - else \
> - asm qual ("addb %1, "__percpu_arg(0) \
> - : "+m" (var) \
> - : "qi" ((pao_T__)(val))); \
> - break; \
> - case 2: \
> - if (pao_ID__ == 1) \
> - asm qual ("incw "__percpu_arg(0) : "+m" (var)); \
> - else if (pao_ID__ == -1) \
> - asm qual ("decw "__percpu_arg(0) : "+m" (var)); \
> - else \
> - asm qual ("addw %1, "__percpu_arg(0) \
> - : "+m" (var) \
> - : "ri" ((pao_T__)(val))); \
> - break; \
> - case 4: \
> - if (pao_ID__ == 1) \
> - asm qual ("incl "__percpu_arg(0) : "+m" (var)); \
> - else if (pao_ID__ == -1) \
> - asm qual ("decl "__percpu_arg(0) : "+m" (var)); \
> - else \
> - asm qual ("addl %1, "__percpu_arg(0) \
> - : "+m" (var) \
> - : "ri" ((pao_T__)(val))); \
> - break; \
> - case 8: \
> - if (pao_ID__ == 1) \
> - asm qual ("incq "__percpu_arg(0) : "+m" (var)); \
> - else if (pao_ID__ == -1) \
> - asm qual ("decq "__percpu_arg(0) : "+m" (var)); \
> - else \
> - asm qual ("addq %1, "__percpu_arg(0) \
> - : "+m" (var) \
> - : "re" ((pao_T__)(val))); \
> - break; \
> - default: __bad_percpu_size(); \
> - } \
> + if (pao_ID__ == 1) \
> + percpu_unary_op(size, qual, "inc", var); \
> + else if (pao_ID__ == -1) \
> + percpu_unary_op(size, qual, "dec", var); \
> + else \
> + percpu_to_op(size, qual, "add", var, val); \
Nice simplification, and it was clever of you to reuse percpu_to_op()
for the case of addition!
In terms of the 0day bot test failures:
>> include/linux/percpu-rwsem.h:91:17: sparse: sparse: cast truncates bits from constant value (ffffffff becomes ffff)
>> include/net/tcp.h:1521:9: sparse: sparse: cast truncates bits from constant value (1d4c0 becomes d4c0)
>> include/net/sch_generic.h:888:9: sparse: sparse: cast truncates bits from constant value (ffffffff becomes ffff)
>> drivers/infiniband/hw/hfi1/pio_copy.c:164:9: sparse: sparse: cast truncates bits from constant value (ffffffff becomes ffff)
which is reminiscent of our discussion in:
https://lore.kernel.org/lkml/CAMzpN2gu4stkRKTsMTVxyzckO3SMhfA+dmCnSu6-aMg5QAA_JQ@xxxxxxxxxxxxxx/
I'm not able to repro with i386_defconfig, but it looks like one
report was i386_allmodconfig, the other was (64b) allyesconfig.
I am able to repro with:
$ rm -f drivers/infiniband/hw/hfi1/pio_copy.o
$ make -j71 CC=clang allyesconfig
$ make -j71 CC=clang C=1 drivers/infiniband/hw/hfi1/pio_copy.o
It's not immediately clear to me from this diff which cast sparse is
complaining about. Looking at the report and expanding this_cpu_dec()
seems to eventually expand to `this_cpu_add_<number>, so the reporting
does look potentially against the right patch in the series. (Seeing
`(typeof((ptr) + 0))NULL` in __verify_pcpu_ptr() in
include/linux/percpu-defs.h is a real WTF, though the comment
explains).
Indeed, if I checkout before the series is applied, the warnings
disappear. So let's follow up tomorrow on where this is coming from.
> } while (0)
>
> #define percpu_from_op(size, qual, op, _var) \
> @@ -228,29 +196,6 @@ do { \
> pfo_ret__; \
> })
>
> -#define percpu_unary_op(qual, op, var) \
> -({ \
> - switch (sizeof(var)) { \
> - case 1: \
> - asm qual (op "b "__percpu_arg(0) \
> - : "+m" (var)); \
> - break; \
> - case 2: \
> - asm qual (op "w "__percpu_arg(0) \
> - : "+m" (var)); \
> - break; \
> - case 4: \
> - asm qual (op "l "__percpu_arg(0) \
> - : "+m" (var)); \
> - break; \
> - case 8: \
> - asm qual (op "q "__percpu_arg(0) \
> - : "+m" (var)); \
> - break; \
> - default: __bad_percpu_size(); \
> - } \
> -})
> -
> /*
> * Add return operation
> */
> @@ -388,9 +333,9 @@ do { \
> #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)
> #define raw_cpu_write_4(pcp, val) percpu_to_op(4, , "mov", (pcp), val)
> -#define raw_cpu_add_1(pcp, val) percpu_add_op(, (pcp), val)
> -#define raw_cpu_add_2(pcp, val) percpu_add_op(, (pcp), val)
> -#define raw_cpu_add_4(pcp, val) percpu_add_op(, (pcp), val)
> +#define raw_cpu_add_1(pcp, val) percpu_add_op(1, , (pcp), val)
> +#define raw_cpu_add_2(pcp, val) percpu_add_op(2, , (pcp), val)
> +#define raw_cpu_add_4(pcp, val) percpu_add_op(4, , (pcp), val)
> #define raw_cpu_and_1(pcp, val) percpu_to_op(1, , "and", (pcp), val)
> #define raw_cpu_and_2(pcp, val) percpu_to_op(2, , "and", (pcp), val)
> #define raw_cpu_and_4(pcp, val) percpu_to_op(4, , "and", (pcp), val)
> @@ -419,9 +364,9 @@ do { \
> #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)
> -#define this_cpu_add_1(pcp, val) percpu_add_op(volatile, (pcp), val)
> -#define this_cpu_add_2(pcp, val) percpu_add_op(volatile, (pcp), val)
> -#define this_cpu_add_4(pcp, val) percpu_add_op(volatile, (pcp), val)
> +#define this_cpu_add_1(pcp, val) percpu_add_op(1, volatile, (pcp), val)
> +#define this_cpu_add_2(pcp, val) percpu_add_op(2, volatile, (pcp), val)
> +#define this_cpu_add_4(pcp, val) percpu_add_op(4, volatile, (pcp), val)
> #define this_cpu_and_1(pcp, val) percpu_to_op(1, volatile, "and", (pcp), val)
> #define this_cpu_and_2(pcp, val) percpu_to_op(2, volatile, "and", (pcp), val)
> #define this_cpu_and_4(pcp, val) percpu_to_op(4, volatile, "and", (pcp), val)
> @@ -470,7 +415,7 @@ do { \
> #ifdef CONFIG_X86_64
> #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_add_8(pcp, val) percpu_add_op(8, , (pcp), val)
> #define raw_cpu_and_8(pcp, val) percpu_to_op(8, , "and", (pcp), val)
> #define raw_cpu_or_8(pcp, val) percpu_to_op(8, , "or", (pcp), val)
> #define raw_cpu_add_return_8(pcp, val) percpu_add_return_op(, pcp, val)
> @@ -479,7 +424,7 @@ do { \
>
> #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_add_8(pcp, val) percpu_add_op(8, volatile, (pcp), val)
> #define this_cpu_and_8(pcp, val) percpu_to_op(8, volatile, "and", (pcp), val)
> #define this_cpu_or_8(pcp, val) percpu_to_op(8, volatile, "or", (pcp), val)
> #define this_cpu_add_return_8(pcp, val) percpu_add_return_op(volatile, pcp, val)
> --
> 2.25.4
>
--
Thanks,
~Nick Desaulniers