From mboxrd@z Thu Jan  1 00:00:00 1970
From: Boqun Feng <boqun.feng@gmail.com>
Date: Tue, 05 Jan 2016 09:53:41 +0000
Subject: Re: [PATCH v2 15/32] powerpc: define __smp_xxx
Message-Id: <20160105095341.GA5321@fixme-laptop.cn.ibm.com>
List-Id: <linux-sh.vger.kernel.org>
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 <1451572003-2440-16-git-send-email-mst@redhat.com>
 <20160105013648.GA1256@fixme-laptop.cn.ibm.com>
 <20160105085117.GA11858@redhat.com>
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To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: linux-kernel@vger.kernel.org, Peter Zijlstra <peterz@infradead.org>, Arnd Bergmann <arnd@arndb.de>, linux-arch@vger.kernel.org, Andrew Cooper <andrew.cooper3@citrix.com>, virtualization@lists.linux-foundation.org, Stefano Stabellini <stefano.stabellini@eu.citrix.com>, Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>, "H. Peter Anvin" <hpa@zytor.com>, David Miller <davem@davemloft.net>, linux-ia64@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, sparclinux@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-metag@vger.kernel.org, linux-mips@linux-mips.org, x86@kernel.org, user-mode-linux-devel@lists.sourceforge.net, adi-buildroot-devel@lists.sourceforge.net, linux-sh@vger.kernel.org, linux-xtensa@linux-xtensa.org, xen-devel@lists.xenproject.org, Benjamin Herrenschmidt <benh@kernel.crashing.org>, Paul Mackerras <paul>

On Tue, Jan 05, 2016 at 10:51:17AM +0200, Michael S. Tsirkin wrote:
> On Tue, Jan 05, 2016 at 09:36:55AM +0800, Boqun Feng wrote:
> > Hi Michael,
> > 
> > On Thu, Dec 31, 2015 at 09:07:42PM +0200, Michael S. Tsirkin wrote:
> > > This defines __smp_xxx barriers for powerpc
> > > for use by virtualization.
> > > 
> > > smp_xxx barriers are removed as they are
> > > defined correctly by asm-generic/barriers.h
> 
> I think this is the part that was missed in review.
> 

Yes, I realized my mistake after reread the series. But smp_lwsync() is
not defined in asm-generic/barriers.h, right?

> > > This reduces the amount of arch-specific boiler-plate code.
> > > 
> > > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > > Acked-by: Arnd Bergmann <arnd@arndb.de>
> > > ---
> > >  arch/powerpc/include/asm/barrier.h | 24 ++++++++----------------
> > >  1 file changed, 8 insertions(+), 16 deletions(-)
> > > 
> > > diff --git a/arch/powerpc/include/asm/barrier.h b/arch/powerpc/include/asm/barrier.h
> > > index 980ad0c..c0deafc 100644
> > > --- a/arch/powerpc/include/asm/barrier.h
> > > +++ b/arch/powerpc/include/asm/barrier.h
> > > @@ -44,19 +44,11 @@
> > >  #define dma_rmb()	__lwsync()
> > >  #define dma_wmb()	__asm__ __volatile__ (stringify_in_c(SMPWMB) : : :"memory")
> > >  
> > > -#ifdef CONFIG_SMP
> > > -#define smp_lwsync()	__lwsync()
> > > +#define __smp_lwsync()	__lwsync()
> > >  
> > 
> > so __smp_lwsync() is always mapped to lwsync, right?
> 
> Yes.
> 
> > > -#define smp_mb()	mb()
> > > -#define smp_rmb()	__lwsync()
> > > -#define smp_wmb()	__asm__ __volatile__ (stringify_in_c(SMPWMB) : : :"memory")
> > > -#else
> > > -#define smp_lwsync()	barrier()
> > > -
> > > -#define smp_mb()	barrier()
> > > -#define smp_rmb()	barrier()
> > > -#define smp_wmb()	barrier()
> > > -#endif /* CONFIG_SMP */
> > > +#define __smp_mb()	mb()
> > > +#define __smp_rmb()	__lwsync()
> > > +#define __smp_wmb()	__asm__ __volatile__ (stringify_in_c(SMPWMB) : : :"memory")
> > >  
> > >  /*
> > >   * This is a barrier which prevents following instructions from being
> > > @@ -67,18 +59,18 @@
> > >  #define data_barrier(x)	\
> > >  	asm volatile("twi 0,%0,0; isync" : : "r" (x) : "memory");
> > >  
> > > -#define smp_store_release(p, v)						\
> > > +#define __smp_store_release(p, v)						\
> > >  do {									\
> > >  	compiletime_assert_atomic_type(*p);				\
> > > -	smp_lwsync();							\
> > > +	__smp_lwsync();							\
> > 
> > , therefore this will emit an lwsync no matter SMP or UP.
> 
> Absolutely. But smp_store_release (without __) will not.
> 
> Please note I did test this: for ppc code before and after
> this patch generates exactly the same binary on SMP and UP.
> 

Yes, you're right, sorry for my mistake...

> 
> > Another thing is that smp_lwsync() may have a third user(other than
> > smp_load_acquire() and smp_store_release()):
> > 
> > http://article.gmane.org/gmane.linux.ports.ppc.embedded/89877
> > 
> > I'm OK to change my patch accordingly, but do we really want
> > smp_lwsync() get involved in this cleanup? If I understand you
> > correctly, this cleanup focuses on external API like smp_{r,w,}mb(),
> > while smp_lwsync() is internal to PPC.
> > 
> > Regards,
> > Boqun
> 
> I think you missed the leading ___ :)
> 

What I mean here was smp_lwsync() was originally internal to PPC, but
never mind ;-)

> smp_store_release is external and it needs __smp_lwsync as
> defined here.
> 
> I can duplicate some code and have smp_lwsync *not* call __smp_lwsync

You mean bringing smp_lwsync() back? because I haven't seen you defining
in asm-generic/barriers.h in previous patches and you just delete it in
this patch.

> but why do this? Still, if you prefer it this way,
> please let me know.
> 

I think deleting smp_lwsync() is fine, though I need to change atomic
variants patches on PPC because of it ;-/

Regards,
Boqun

> > >  	WRITE_ONCE(*p, v);						\
> > >  } while (0)
> > >  
> > > -#define smp_load_acquire(p)						\
> > > +#define __smp_load_acquire(p)						\
> > >  ({									\
> > >  	typeof(*p) ___p1 = READ_ONCE(*p);				\
> > >  	compiletime_assert_atomic_type(*p);				\
> > > -	smp_lwsync();							\
> > > +	__smp_lwsync();							\
> > >  	___p1;								\
> > >  })
> > >  
> > > -- 
> > > MST
> > > 
> > > --
> > > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> > > the body of a message to majordomo@vger.kernel.org
> > > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> > > Please read the FAQ at  http://www.tux.org/lkml/

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Date: Tue, 5 Jan 2016 17:53:41 +0800
From: Boqun Feng <boqun.feng@gmail.com>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: linux-kernel@vger.kernel.org, Peter Zijlstra <peterz@infradead.org>,
        Arnd Bergmann <arnd@arndb.de>, linux-arch@vger.kernel.org,
        Andrew Cooper <andrew.cooper3@citrix.com>,
        virtualization@lists.linux-foundation.org,
        Stefano Stabellini <stefano.stabellini@eu.citrix.com>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>,
        "H. Peter Anvin" <hpa@zytor.com>, David Miller <davem@davemloft.net>,
        linux-ia64@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        linux-s390@vger.kernel.org, sparclinux@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, linux-metag@vger.kernel.org,
        linux-mips@linux-mips.org, x86@kernel.org,
        user-mode-linux-devel@lists.sourceforge.net,
        adi-buildroot-devel@lists.sourceforge.net, linux-sh@vger.kernel.org,
        linux-xtensa@linux-xtensa.org, xen-devel@lists.xenproject.org,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>, Ingo Molnar <mingo@kernel.org>,
        Davidlohr Bueso <dave@stgolabs.net>,
        Andrey Konovalov <andreyknvl@google.com>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: Re: [PATCH v2 15/32] powerpc: define __smp_xxx
Message-ID: <20160105095341.GA5321@fixme-laptop.cn.ibm.com>
References: <1451572003-2440-1-git-send-email-mst@redhat.com>
 <1451572003-2440-16-git-send-email-mst@redhat.com>
 <20160105013648.GA1256@fixme-laptop.cn.ibm.com>
 <20160105085117.GA11858@redhat.com>
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On Tue, Jan 05, 2016 at 10:51:17AM +0200, Michael S. Tsirkin wrote:
> On Tue, Jan 05, 2016 at 09:36:55AM +0800, Boqun Feng wrote:
> > Hi Michael,
> > 
> > On Thu, Dec 31, 2015 at 09:07:42PM +0200, Michael S. Tsirkin wrote:
> > > This defines __smp_xxx barriers for powerpc
> > > for use by virtualization.
> > > 
> > > smp_xxx barriers are removed as they are
> > > defined correctly by asm-generic/barriers.h
> 
> I think this is the part that was missed in review.
> 

Yes, I realized my mistake after reread the series. But smp_lwsync() is
not defined in asm-generic/barriers.h, right?

> > > This reduces the amount of arch-specific boiler-plate code.
> > > 
> > > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > > Acked-by: Arnd Bergmann <arnd@arndb.de>
> > > ---
> > >  arch/powerpc/include/asm/barrier.h | 24 ++++++++----------------
> > >  1 file changed, 8 insertions(+), 16 deletions(-)
> > > 
> > > diff --git a/arch/powerpc/include/asm/barrier.h b/arch/powerpc/include/asm/barrier.h
> > > index 980ad0c..c0deafc 100644
> > > --- a/arch/powerpc/include/asm/barrier.h
> > > +++ b/arch/powerpc/include/asm/barrier.h
> > > @@ -44,19 +44,11 @@
> > >  #define dma_rmb()	__lwsync()
> > >  #define dma_wmb()	__asm__ __volatile__ (stringify_in_c(SMPWMB) : : :"memory")
> > >  
> > > -#ifdef CONFIG_SMP
> > > -#define smp_lwsync()	__lwsync()
> > > +#define __smp_lwsync()	__lwsync()
> > >  
> > 
> > so __smp_lwsync() is always mapped to lwsync, right?
> 
> Yes.
> 
> > > -#define smp_mb()	mb()
> > > -#define smp_rmb()	__lwsync()
> > > -#define smp_wmb()	__asm__ __volatile__ (stringify_in_c(SMPWMB) : : :"memory")
> > > -#else
> > > -#define smp_lwsync()	barrier()
> > > -
> > > -#define smp_mb()	barrier()
> > > -#define smp_rmb()	barrier()
> > > -#define smp_wmb()	barrier()
> > > -#endif /* CONFIG_SMP */
> > > +#define __smp_mb()	mb()
> > > +#define __smp_rmb()	__lwsync()
> > > +#define __smp_wmb()	__asm__ __volatile__ (stringify_in_c(SMPWMB) : : :"memory")
> > >  
> > >  /*
> > >   * This is a barrier which prevents following instructions from being
> > > @@ -67,18 +59,18 @@
> > >  #define data_barrier(x)	\
> > >  	asm volatile("twi 0,%0,0; isync" : : "r" (x) : "memory");
> > >  
> > > -#define smp_store_release(p, v)						\
> > > +#define __smp_store_release(p, v)						\
> > >  do {									\
> > >  	compiletime_assert_atomic_type(*p);				\
> > > -	smp_lwsync();							\
> > > +	__smp_lwsync();							\
> > 
> > , therefore this will emit an lwsync no matter SMP or UP.
> 
> Absolutely. But smp_store_release (without __) will not.
> 
> Please note I did test this: for ppc code before and after
> this patch generates exactly the same binary on SMP and UP.
> 

Yes, you're right, sorry for my mistake...

> 
> > Another thing is that smp_lwsync() may have a third user(other than
> > smp_load_acquire() and smp_store_release()):
> > 
> > http://article.gmane.org/gmane.linux.ports.ppc.embedded/89877
> > 
> > I'm OK to change my patch accordingly, but do we really want
> > smp_lwsync() get involved in this cleanup? If I understand you
> > correctly, this cleanup focuses on external API like smp_{r,w,}mb(),
> > while smp_lwsync() is internal to PPC.
> > 
> > Regards,
> > Boqun
> 
> I think you missed the leading ___ :)
> 

What I mean here was smp_lwsync() was originally internal to PPC, but
never mind ;-)

> smp_store_release is external and it needs __smp_lwsync as
> defined here.
> 
> I can duplicate some code and have smp_lwsync *not* call __smp_lwsync

You mean bringing smp_lwsync() back? because I haven't seen you defining
in asm-generic/barriers.h in previous patches and you just delete it in
this patch.

> but why do this? Still, if you prefer it this way,
> please let me know.
> 

I think deleting smp_lwsync() is fine, though I need to change atomic
variants patches on PPC because of it ;-/

Regards,
Boqun

> > >  	WRITE_ONCE(*p, v);						\
> > >  } while (0)
> > >  
> > > -#define smp_load_acquire(p)						\
> > > +#define __smp_load_acquire(p)						\
> > >  ({									\
> > >  	typeof(*p) ___p1 = READ_ONCE(*p);				\
> > >  	compiletime_assert_atomic_type(*p);				\
> > > -	smp_lwsync();							\
> > > +	__smp_lwsync();							\
> > >  	___p1;								\
> > >  })
> > >  
> > > -- 
> > > MST
> > > 
> > > --
> > > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> > > the body of a message to majordomo@vger.kernel.org
> > > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> > > Please read the FAQ at  http://www.tux.org/lkml/

From mboxrd@z Thu Jan  1 00:00:00 1970
From: Boqun Feng <boqun.feng@gmail.com>
Subject: Re: [PATCH v2 15/32] powerpc: define __smp_xxx
Date: Tue, 5 Jan 2016 17:53:41 +0800
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To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: linux-kernel@vger.kernel.org, Peter Zijlstra <peterz@infradead.org>, Arnd Bergmann <arnd@arndb.de>, linux-arch@vger.kernel.org, Andrew Cooper <andrew.cooper3@citrix.com>, virtualization@lists.linux-foundation.org, Stefano Stabellini <stefano.stabellini@eu.citrix.com>, Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>, "H. Peter Anvin" <hpa@zytor.com>, David Miller <davem@davemloft.net>, linux-ia64@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, sparclinux@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-metag@vger.kernel.org, linux-mips@linux-mips.org, x86@kernel.org, user-mode-linux-devel@lists.sourceforge.net, adi-buildroot-devel@lists.sourceforge.net, linux-sh@vger.kernel.org, linux-xtensa@linux-xtensa.org, xen-devel@lists.xenproject.org, Benjamin Herrenschmidt <benh@kernel.crashing.org>, Paul Mackerras <paul>
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On Tue, Jan 05, 2016 at 10:51:17AM +0200, Michael S. Tsirkin wrote:
> On Tue, Jan 05, 2016 at 09:36:55AM +0800, Boqun Feng wrote:
> > Hi Michael,
> > 
> > On Thu, Dec 31, 2015 at 09:07:42PM +0200, Michael S. Tsirkin wrote:
> > > This defines __smp_xxx barriers for powerpc
> > > for use by virtualization.
> > > 
> > > smp_xxx barriers are removed as they are
> > > defined correctly by asm-generic/barriers.h
> 
> I think this is the part that was missed in review.
> 

Yes, I realized my mistake after reread the series. But smp_lwsync() is
not defined in asm-generic/barriers.h, right?

> > > This reduces the amount of arch-specific boiler-plate code.
> > > 
> > > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > > Acked-by: Arnd Bergmann <arnd@arndb.de>
> > > ---
> > >  arch/powerpc/include/asm/barrier.h | 24 ++++++++----------------
> > >  1 file changed, 8 insertions(+), 16 deletions(-)
> > > 
> > > diff --git a/arch/powerpc/include/asm/barrier.h b/arch/powerpc/include/asm/barrier.h
> > > index 980ad0c..c0deafc 100644
> > > --- a/arch/powerpc/include/asm/barrier.h
> > > +++ b/arch/powerpc/include/asm/barrier.h
> > > @@ -44,19 +44,11 @@
> > >  #define dma_rmb()	__lwsync()
> > >  #define dma_wmb()	__asm__ __volatile__ (stringify_in_c(SMPWMB) : : :"memory")
> > >  
> > > -#ifdef CONFIG_SMP
> > > -#define smp_lwsync()	__lwsync()
> > > +#define __smp_lwsync()	__lwsync()
> > >  
> > 
> > so __smp_lwsync() is always mapped to lwsync, right?
> 
> Yes.
> 
> > > -#define smp_mb()	mb()
> > > -#define smp_rmb()	__lwsync()
> > > -#define smp_wmb()	__asm__ __volatile__ (stringify_in_c(SMPWMB) : : :"memory")
> > > -#else
> > > -#define smp_lwsync()	barrier()
> > > -
> > > -#define smp_mb()	barrier()
> > > -#define smp_rmb()	barrier()
> > > -#define smp_wmb()	barrier()
> > > -#endif /* CONFIG_SMP */
> > > +#define __smp_mb()	mb()
> > > +#define __smp_rmb()	__lwsync()
> > > +#define __smp_wmb()	__asm__ __volatile__ (stringify_in_c(SMPWMB) : : :"memory")
> > >  
> > >  /*
> > >   * This is a barrier which prevents following instructions from being
> > > @@ -67,18 +59,18 @@
> > >  #define data_barrier(x)	\
> > >  	asm volatile("twi 0,%0,0; isync" : : "r" (x) : "memory");
> > >  
> > > -#define smp_store_release(p, v)						\
> > > +#define __smp_store_release(p, v)						\
> > >  do {									\
> > >  	compiletime_assert_atomic_type(*p);				\
> > > -	smp_lwsync();							\
> > > +	__smp_lwsync();							\
> > 
> > , therefore this will emit an lwsync no matter SMP or UP.
> 
> Absolutely. But smp_store_release (without __) will not.
> 
> Please note I did test this: for ppc code before and after
> this patch generates exactly the same binary on SMP and UP.
> 

Yes, you're right, sorry for my mistake...

> 
> > Another thing is that smp_lwsync() may have a third user(other than
> > smp_load_acquire() and smp_store_release()):
> > 
> > http://article.gmane.org/gmane.linux.ports.ppc.embedded/89877
> > 
> > I'm OK to change my patch accordingly, but do we really want
> > smp_lwsync() get involved in this cleanup? If I understand you
> > correctly, this cleanup focuses on external API like smp_{r,w,}mb(),
> > while smp_lwsync() is internal to PPC.
> > 
> > Regards,
> > Boqun
> 
> I think you missed the leading ___ :)
> 

What I mean here was smp_lwsync() was originally internal to PPC, but
never mind ;-)

> smp_store_release is external and it needs __smp_lwsync as
> defined here.
> 
> I can duplicate some code and have smp_lwsync *not* call __smp_lwsync

You mean bringing smp_lwsync() back? because I haven't seen you defining
in asm-generic/barriers.h in previous patches and you just delete it in
this patch.

> but why do this? Still, if you prefer it this way,
> please let me know.
> 

I think deleting smp_lwsync() is fine, though I need to change atomic
variants patches on PPC because of it ;-/

Regards,
Boqun

> > >  	WRITE_ONCE(*p, v);						\
> > >  } while (0)
> > >  
> > > -#define smp_load_acquire(p)						\
> > > +#define __smp_load_acquire(p)						\
> > >  ({									\
> > >  	typeof(*p) ___p1 = READ_ONCE(*p);				\
> > >  	compiletime_assert_atomic_type(*p);				\
> > > -	smp_lwsync();							\
> > > +	__smp_lwsync();							\
> > >  	___p1;								\
> > >  })
> > >  
> > > -- 
> > > MST
> > > 
> > > --
> > > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> > > the body of a message to majordomo@vger.kernel.org
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From mboxrd@z Thu Jan  1 00:00:00 1970
From: boqun.feng@gmail.com (Boqun Feng)
Date: Tue, 5 Jan 2016 17:53:41 +0800
Subject: [PATCH v2 15/32] powerpc: define __smp_xxx
In-Reply-To: <20160105085117.GA11858@redhat.com>
References: <1451572003-2440-1-git-send-email-mst@redhat.com>
 <1451572003-2440-16-git-send-email-mst@redhat.com>
 <20160105013648.GA1256@fixme-laptop.cn.ibm.com>
 <20160105085117.GA11858@redhat.com>
Message-ID: <20160105095341.GA5321@fixme-laptop.cn.ibm.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Tue, Jan 05, 2016 at 10:51:17AM +0200, Michael S. Tsirkin wrote:
> On Tue, Jan 05, 2016 at 09:36:55AM +0800, Boqun Feng wrote:
> > Hi Michael,
> > 
> > On Thu, Dec 31, 2015 at 09:07:42PM +0200, Michael S. Tsirkin wrote:
> > > This defines __smp_xxx barriers for powerpc
> > > for use by virtualization.
> > > 
> > > smp_xxx barriers are removed as they are
> > > defined correctly by asm-generic/barriers.h
> 
> I think this is the part that was missed in review.
> 

Yes, I realized my mistake after reread the series. But smp_lwsync() is
not defined in asm-generic/barriers.h, right?

> > > This reduces the amount of arch-specific boiler-plate code.
> > > 
> > > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > > Acked-by: Arnd Bergmann <arnd@arndb.de>
> > > ---
> > >  arch/powerpc/include/asm/barrier.h | 24 ++++++++----------------
> > >  1 file changed, 8 insertions(+), 16 deletions(-)
> > > 
> > > diff --git a/arch/powerpc/include/asm/barrier.h b/arch/powerpc/include/asm/barrier.h
> > > index 980ad0c..c0deafc 100644
> > > --- a/arch/powerpc/include/asm/barrier.h
> > > +++ b/arch/powerpc/include/asm/barrier.h
> > > @@ -44,19 +44,11 @@
> > >  #define dma_rmb()	__lwsync()
> > >  #define dma_wmb()	__asm__ __volatile__ (stringify_in_c(SMPWMB) : : :"memory")
> > >  
> > > -#ifdef CONFIG_SMP
> > > -#define smp_lwsync()	__lwsync()
> > > +#define __smp_lwsync()	__lwsync()
> > >  
> > 
> > so __smp_lwsync() is always mapped to lwsync, right?
> 
> Yes.
> 
> > > -#define smp_mb()	mb()
> > > -#define smp_rmb()	__lwsync()
> > > -#define smp_wmb()	__asm__ __volatile__ (stringify_in_c(SMPWMB) : : :"memory")
> > > -#else
> > > -#define smp_lwsync()	barrier()
> > > -
> > > -#define smp_mb()	barrier()
> > > -#define smp_rmb()	barrier()
> > > -#define smp_wmb()	barrier()
> > > -#endif /* CONFIG_SMP */
> > > +#define __smp_mb()	mb()
> > > +#define __smp_rmb()	__lwsync()
> > > +#define __smp_wmb()	__asm__ __volatile__ (stringify_in_c(SMPWMB) : : :"memory")
> > >  
> > >  /*
> > >   * This is a barrier which prevents following instructions from being
> > > @@ -67,18 +59,18 @@
> > >  #define data_barrier(x)	\
> > >  	asm volatile("twi 0,%0,0; isync" : : "r" (x) : "memory");
> > >  
> > > -#define smp_store_release(p, v)						\
> > > +#define __smp_store_release(p, v)						\
> > >  do {									\
> > >  	compiletime_assert_atomic_type(*p);				\
> > > -	smp_lwsync();							\
> > > +	__smp_lwsync();							\
> > 
> > , therefore this will emit an lwsync no matter SMP or UP.
> 
> Absolutely. But smp_store_release (without __) will not.
> 
> Please note I did test this: for ppc code before and after
> this patch generates exactly the same binary on SMP and UP.
> 

Yes, you're right, sorry for my mistake...

> 
> > Another thing is that smp_lwsync() may have a third user(other than
> > smp_load_acquire() and smp_store_release()):
> > 
> > http://article.gmane.org/gmane.linux.ports.ppc.embedded/89877
> > 
> > I'm OK to change my patch accordingly, but do we really want
> > smp_lwsync() get involved in this cleanup? If I understand you
> > correctly, this cleanup focuses on external API like smp_{r,w,}mb(),
> > while smp_lwsync() is internal to PPC.
> > 
> > Regards,
> > Boqun
> 
> I think you missed the leading ___ :)
> 

What I mean here was smp_lwsync() was originally internal to PPC, but
never mind ;-)

> smp_store_release is external and it needs __smp_lwsync as
> defined here.
> 
> I can duplicate some code and have smp_lwsync *not* call __smp_lwsync

You mean bringing smp_lwsync() back? because I haven't seen you defining
in asm-generic/barriers.h in previous patches and you just delete it in
this patch.

> but why do this? Still, if you prefer it this way,
> please let me know.
> 

I think deleting smp_lwsync() is fine, though I need to change atomic
variants patches on PPC because of it ;-/

Regards,
Boqun

> > >  	WRITE_ONCE(*p, v);						\
> > >  } while (0)
> > >  
> > > -#define smp_load_acquire(p)						\
> > > +#define __smp_load_acquire(p)						\
> > >  ({									\
> > >  	typeof(*p) ___p1 = READ_ONCE(*p);				\
> > >  	compiletime_assert_atomic_type(*p);				\
> > > -	smp_lwsync();							\
> > > +	__smp_lwsync();							\
> > >  	___p1;								\
> > >  })
> > >  
> > > -- 
> > > MST
> > > 
> > > --
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