linux-kernel - Re: [PATCH v4 2/5] arm64: barrier: Add smp_cond_load_relaxed

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Message-ID: <878qiwqxzf.fsf@oracle.com>
Date: Tue, 02 Sep 2025 15:40:52 -0700
From: Ankur Arora <ankur.a.arora@...cle.com>
To: Catalin Marinas <catalin.marinas@....com>
Cc: Ankur Arora <ankur.a.arora@...cle.com>, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        bpf@...r.kernel.org, arnd@...db.de, will@...nel.org,
        peterz@...radead.org, akpm@...ux-foundation.org, mark.rutland@....com,
        harisokn@...zon.com, cl@...two.org, ast@...nel.org, memxor@...il.com,
        zhenglifeng1@...wei.com, xueshuai@...ux.alibaba.com,
        joao.m.martins@...cle.com, boris.ostrovsky@...cle.com,
        konrad.wilk@...cle.com
Subject: Re: [PATCH v4 2/5] arm64: barrier: Add
 smp_cond_load_relaxed_timewait()


Catalin Marinas <catalin.marinas@....com> writes:

> On Fri, Aug 29, 2025 at 01:07:32AM -0700, Ankur Arora wrote:
>> diff --git a/arch/arm64/include/asm/barrier.h b/arch/arm64/include/asm/barrier.h
>> index f5801b0ba9e9..9b29abc212db 100644
>> --- a/arch/arm64/include/asm/barrier.h
>> +++ b/arch/arm64/include/asm/barrier.h
>> @@ -219,6 +219,28 @@ do {									\
>>  	(typeof(*ptr))VAL;						\
>>  })
>>
>> +extern bool arch_timer_evtstrm_available(void);
>
> In theory, this doesn't work if CONFIG_ARM_ARCH_TIMER is disabled,
> though that's not the case for arm64. Maybe add a short comment that's
> re-declared here to avoid include dependencies.

Will add.

Thanks
Ankur

>> +
>> +#define smp_cond_load_relaxed_timewait(ptr, cond_expr, time_check_expr)	\
>> +({									\
>> +	typeof(ptr) __PTR = (ptr);					\
>> +	__unqual_scalar_typeof(*ptr) VAL;				\
>> +	bool __wfe = arch_timer_evtstrm_available();			\
>> +									\
>> +	for (;;) {							\
>> +		VAL = READ_ONCE(*__PTR);				\
>> +		if (cond_expr)						\
>> +			break;						\
>> +		if (time_check_expr)					\
>> +			break;						\
>> +		if (likely(__wfe))					\
>> +			__cmpwait_relaxed(__PTR, VAL);			\
>> +		else							\
>> +			cpu_relax();					\
>> +	}								\
>> +	(typeof(*ptr)) VAL;						\
>> +})
>> +
>>  #include <asm-generic/barrier.h>
>>
>>  #endif	/* __ASSEMBLY__ */
>
> Reviewed-by: Catalin Marinas <catalin.marinas@....com>


--
ankur