netdev - Re: [PATCHv5 2/2] memory barrier: adding smp_mb__after

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Date:	Fri, 03 Jul 2009 11:20:20 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Jiri Olsa <jolsa@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	fbl@...hat.com, nhorman@...hat.com, davem@...hat.com,
	htejun@...il.com, jarkao2@...il.com, oleg@...hat.com,
	davidel@...ilserver.org
Subject: Re: [PATCHv5 2/2] memory barrier: adding smp_mb__after_lock

Ingo Molnar a écrit :
> * Jiri Olsa <jolsa@...hat.com> wrote:
> 
>> +++ b/arch/x86/include/asm/spinlock.h
>> @@ -302,4 +302,7 @@ static inline void __raw_write_unlock(raw_rwlock_t *rw)
>>  #define _raw_read_relax(lock)	cpu_relax()
>>  #define _raw_write_relax(lock)	cpu_relax()
>>  
>> +/* The {read|write|spin}_lock() on x86 are full memory barriers. */
>> +#define smp_mb__after_lock() do { } while (0)
> 
> Two small stylistic comments, please make this an inline function:
> 
> static inline void smp_mb__after_lock(void) { }
> #define smp_mb__after_lock
> 
> (untested)
> 
>> +/* The lock does not imply full memory barrier. */
>> +#ifndef smp_mb__after_lock
>> +#define smp_mb__after_lock() smp_mb()
>> +#endif
> 
> ditto.
> 
> 	Ingo

This was following existing implementations of various smp_mb__??? helpers :

# grep -4 smp_mb__before_clear_bit include/asm-generic/bitops.h

/*
 * clear_bit may not imply a memory barrier
 */
#ifndef smp_mb__before_clear_bit
#define smp_mb__before_clear_bit()      smp_mb()
#define smp_mb__after_clear_bit()       smp_mb()
#endif


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