linux-kernel - Re: [PATCH v2 09/10] arch: Remove cmpxchg

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Message-ID: <Y+OnUXkKcT2Y7Yiq@localhost>
Date:   Wed, 8 Feb 2023 13:44:49 +0000
From:   Hyeonggon Yoo <42.hyeyoo@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     torvalds@...ux-foundation.org, corbet@....net, will@...nel.org,
        boqun.feng@...il.com, mark.rutland@....com,
        catalin.marinas@....com, dennis@...nel.org, tj@...nel.org,
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        agordeev@...ux.ibm.com, borntraeger@...ux.ibm.com,
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        bp@...en8.de, dave.hansen@...ux.intel.com, x86@...nel.org,
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        baolu.lu@...ux.intel.com, Arnd Bergmann <arnd@...db.de>,
        Herbert Xu <herbert@...dor.apana.org.au>, davem@...emloft.net,
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        Andrew Morton <akpm@...ux-foundation.org>, vbabka@...e.cz,
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        linux-arch@...r.kernel.org, linux-crypto@...r.kernel.org
Subject: Re: [PATCH v2 09/10] arch: Remove cmpxchg_double

On Thu, Feb 02, 2023 at 03:50:39PM +0100, Peter Zijlstra wrote:
> No moar users, remove the monster.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>  Documentation/core-api/this_cpu_ops.rst    |    2 -
>  arch/arm64/include/asm/atomic_ll_sc.h      |   33 ----------------
>  arch/arm64/include/asm/atomic_lse.h        |   36 ------------------
>  arch/arm64/include/asm/cmpxchg.h           |   46 -----------------------
>  arch/arm64/include/asm/percpu.h            |   10 -----
>  arch/s390/include/asm/cmpxchg.h            |   34 -----------------
>  arch/s390/include/asm/percpu.h             |   18 ---------
>  arch/x86/include/asm/cmpxchg.h             |   25 ------------
>  arch/x86/include/asm/cmpxchg_32.h          |    1 
>  arch/x86/include/asm/cmpxchg_64.h          |    1 
>  arch/x86/include/asm/percpu.h              |   41 --------------------
>  include/asm-generic/percpu.h               |   58 -----------------------------
>  include/linux/atomic/atomic-instrumented.h |   17 --------
>  include/linux/percpu-defs.h                |   38 -------------------
>  scripts/atomic/gen-atomic-instrumented.sh  |   17 ++------
>  15 files changed, 6 insertions(+), 371 deletions(-)
> 
> --- a/arch/x86/include/asm/cmpxchg.h
> +++ b/arch/x86/include/asm/cmpxchg.h
> --- a/arch/x86/include/asm/percpu.h
> +++ b/arch/x86/include/asm/percpu.h
> @@ -385,30 +368,6 @@ do {									\
>  #define this_cpu_add_return_8(pcp, val)		percpu_add_return_op(8, volatile, pcp, val)
>  #define this_cpu_xchg_8(pcp, nval)		percpu_xchg_op(8, volatile, pcp, nval)
>  #define this_cpu_cmpxchg_8(pcp, oval, nval)	percpu_cmpxchg_op(8, volatile, pcp, oval, nval)
> -
> -/*
> - * Pretty complex macro to generate cmpxchg16 instruction.  The instruction
> - * is not supported on early AMD64 processors so we must be able to emulate
> - * it in software.  The address used in the cmpxchg16 instruction must be
> - * aligned to a 16 byte boundary.
> - */
> -#define percpu_cmpxchg16b_double(pcp1, pcp2, o1, o2, n1, n2)		\
> -({									\
> -	bool __ret;							\
> -	typeof(pcp1) __o1 = (o1), __n1 = (n1);				\
> -	typeof(pcp2) __o2 = (o2), __n2 = (n2);				\
> -	alternative_io("leaq %P1,%%rsi\n\tcall this_cpu_cmpxchg16b_emu\n\t", \

I guess now arch/x86/lib/cmpxchg*b_emu.S could be dropped too?

> -		       "cmpxchg16b " __percpu_arg(1) "\n\tsetz %0\n\t",	\
> -		       X86_FEATURE_CX16,				\
> -		       ASM_OUTPUT2("=a" (__ret), "+m" (pcp1),		\
> -				   "+m" (pcp2), "+d" (__o2)),		\
> -		       "b" (__n1), "c" (__n2), "a" (__o1) : "rsi");	\
> -	__ret;								\
> -})
> -
> -#define raw_cpu_cmpxchg_double_8	percpu_cmpxchg16b_double
> -#define this_cpu_cmpxchg_double_8	percpu_cmpxchg16b_double
> -
>  #endif