From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Dumazet <eric.dumazet@gmail.com>
Subject: Re: [PATCHv5 2/2] memory barrier: adding smp_mb__after_lock
Date: Fri, 03 Jul 2009 11:20:20 +0200
Message-ID: <4A4DCD54.1080908@gmail.com>
References: <20090703081219.GE2902@jolsa.lab.eng.brq.redhat.com> <20090703081445.GG2902@jolsa.lab.eng.brq.redhat.com> <20090703090606.GA3902@elte.hu>
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Cc: Jiri Olsa <jolsa@redhat.com>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
	fbl@redhat.com, nhorman@redhat.com, davem@redhat.com,
	htejun@gmail.com, jarkao2@gmail.com, oleg@redhat.com,
	davidel@xmailserver.org
To: Ingo Molnar <mingo@elte.hu>
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Ingo Molnar a =E9crit :
> * Jiri Olsa <jolsa@redhat.com> wrote:
>=20
>> +++ 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()
>> =20
>> +/* The {read|write|spin}_lock() on x86 are full memory barriers. */
>> +#define smp_mb__after_lock() do { } while (0)
>=20
> Two small stylistic comments, please make this an inline function:
>=20
> static inline void smp_mb__after_lock(void) { }
> #define smp_mb__after_lock
>=20
> (untested)
>=20
>> +/* The lock does not imply full memory barrier. */
>> +#ifndef smp_mb__after_lock
>> +#define smp_mb__after_lock() smp_mb()
>> +#endif
>=20
> ditto.
>=20
> 	Ingo

This was following existing implementations of various smp_mb__??? help=
ers :

# 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