linux-kernel - Re: [PATCH] locking/pvqspinlock/x86: Use _Q_LOCKED_VAL in PV_UNLOCK

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Date: Mon, 22 Apr 2024 12:45:25 -0700
From: Boqun Feng <boqun.feng@...il.com>
To: Uros Bizjak <ubizjak@...il.com>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>, Will Deacon <will@...nel.org>,
	Waiman Long <longman@...hat.com>
Subject: Re: [PATCH] locking/pvqspinlock/x86: Use _Q_LOCKED_VAL in
 PV_UNLOCK_ASM macro

On Mon, Apr 22, 2024 at 05:17:35PM +0200, Uros Bizjak wrote:
> Use _Q_LOCKED_VAL instead of hardcoded $0x1 in PV_UNLOCK_ASM macro.
> 
> No functional changes intended.
> 
> Signed-off-by: Uros Bizjak <ubizjak@...il.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Will Deacon <will@...nel.org>
> Cc: Waiman Long <longman@...hat.com>
> Cc: Boqun Feng <boqun.feng@...il.com>
> ---
>  arch/x86/include/asm/qspinlock_paravirt.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/qspinlock_paravirt.h b/arch/x86/include/asm/qspinlock_paravirt.h
> index 466af57b8ed6..0a985784be9b 100644
> --- a/arch/x86/include/asm/qspinlock_paravirt.h
> +++ b/arch/x86/include/asm/qspinlock_paravirt.h
> @@ -40,7 +40,7 @@ __PV_CALLEE_SAVE_REGS_THUNK(__pv_queued_spin_unlock_slowpath, ".spinlock.text");
>  #define PV_UNLOCK_ASM							\
>  	FRAME_BEGIN							\
>  	"push  %rdx\n\t"						\
> -	"mov   $0x1,%eax\n\t"						\
> +	"mov   $" __stringify(_Q_LOCKED_VAL) ",%eax\n\t"		\
>  	"xor   %edx,%edx\n\t"						\
>  	LOCK_PREFIX "cmpxchg %dl,(%rdi)\n\t"				\
>  	"jne   .slowpath\n\t"						\

There is also a "cmp $0x1,%al" afterwards.

Regards,
Boqun

> -- 
> 2.42.0
>