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Re: [PATCH v2 15/32] powerpc: define __smp_xxx

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  Re: [PATCH v2 15/32] powerpc: define __smp_xxx Boqun Feng <boqun.feng@gmail.com> - 2016-01-05 02:40 +0100
    Re: [PATCH v2 15/32] powerpc: define __smp_xxx "Michael S. Tsirkin" <mst@redhat.com> - 2016-01-05 10:00 +0100
      Re: [PATCH v2 15/32] powerpc: define __smp_xxx Boqun Feng <boqun.feng@gmail.com> - 2016-01-05 11:00 +0100
        Re: [PATCH v2 15/32] powerpc: define __smp_xxx "Michael S. Tsirkin" <mst@redhat.com> - 2016-01-05 17:20 +0100
          Re: [PATCH v2 15/32] powerpc: define __smp_xxx Boqun Feng <boqun.feng@gmail.com> - 2016-01-06 03:00 +0100
            Re: [PATCH v2 15/32] powerpc: define __smp_xxx "Michael S. Tsirkin" <mst@redhat.com> - 2016-01-06 21:30 +0100
              Re: [PATCH v2 15/32] powerpc: define __smp_xxx Boqun Feng <boqun.feng@gmail.com> - 2016-01-07 01:50 +0100

#1301226 — Re: [PATCH v2 15/32] powerpc: define __smp_xxx

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
> 
> 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?

> -#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.

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

>  	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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#1301335

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.

> > 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.


> 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 ___ :)

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

> >  	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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#1301382

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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#1301665

On Tue, Jan 05, 2016 at 05:53:41PM +0800, Boqun Feng wrote:
> 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?

It isn't because as far as I could tell it is not used
outside arch/powerpc/include/asm/barrier.h
smp_store_release and smp_load_acquire.

And these are now gone.

Instead there are __smp_store_release and __smp_load_acquire
which call __smp_lwsync.
These are only used for virt and on SMP.
UP variants are generic - they just call barrier().


> > > > 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

Sorry, I don't understand - why do you have to do anything?
I changed all users of smp_lwsync so they
use __smp_lwsync on SMP and barrier() on !SMP.

This is exactly the current behaviour, I also tested that
generated code does not change at all.

Is there a patch in your tree that conflicts with this?


> > > >  	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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#1302328

On Tue, Jan 05, 2016 at 06:16:48PM +0200, Michael S. Tsirkin wrote:
[snip]
> > > > 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
> 
> Sorry, I don't understand - why do you have to do anything?
> I changed all users of smp_lwsync so they
> use __smp_lwsync on SMP and barrier() on !SMP.
> 
> This is exactly the current behaviour, I also tested that
> generated code does not change at all.
> 
> Is there a patch in your tree that conflicts with this?
> 

Because in a patchset which implements atomic relaxed/acquire/release
variants on PPC I use smp_lwsync(), this makes it have another user,
please see this mail:

http://article.gmane.org/gmane.linux.ports.ppc.embedded/89877

in definition of PPC's __atomic_op_release().


But I think removing smp_lwsync() is a good idea and actually I think we
can go further to remove __smp_lwsync() and let __smp_load_acquire and
__smp_store_release call __lwsync() directly, but that is another thing.

Anyway, I will modify my patch.

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/
--
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
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#1303042

On Wed, Jan 06, 2016 at 09:51:52AM +0800, Boqun Feng wrote:
> On Tue, Jan 05, 2016 at 06:16:48PM +0200, Michael S. Tsirkin wrote:
> [snip]
> > > > > 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
> > 
> > Sorry, I don't understand - why do you have to do anything?
> > I changed all users of smp_lwsync so they
> > use __smp_lwsync on SMP and barrier() on !SMP.
> > 
> > This is exactly the current behaviour, I also tested that
> > generated code does not change at all.
> > 
> > Is there a patch in your tree that conflicts with this?
> > 
> 
> Because in a patchset which implements atomic relaxed/acquire/release
> variants on PPC I use smp_lwsync(), this makes it have another user,
> please see this mail:
> 
> http://article.gmane.org/gmane.linux.ports.ppc.embedded/89877
> 
> in definition of PPC's __atomic_op_release().
> 
> 
> But I think removing smp_lwsync() is a good idea and actually I think we
> can go further to remove __smp_lwsync() and let __smp_load_acquire and
> __smp_store_release call __lwsync() directly, but that is another thing.
> 
> Anyway, I will modify my patch.
> 
> Regards,
> Boqun


Thanks!
Could you send an ack then please?

> > 
> > > > > >  	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/
--
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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#1303212

[Multipart message — attachments visible in raw view] — view raw

On Wed, Jan 06, 2016 at 10:23:51PM +0200, Michael S. Tsirkin wrote:
[...]
> > > 
> > > Sorry, I don't understand - why do you have to do anything?
> > > I changed all users of smp_lwsync so they
> > > use __smp_lwsync on SMP and barrier() on !SMP.
> > > 
> > > This is exactly the current behaviour, I also tested that
> > > generated code does not change at all.
> > > 
> > > Is there a patch in your tree that conflicts with this?
> > > 
> > 
> > Because in a patchset which implements atomic relaxed/acquire/release
> > variants on PPC I use smp_lwsync(), this makes it have another user,
> > please see this mail:
> > 
> > http://article.gmane.org/gmane.linux.ports.ppc.embedded/89877
> > 
> > in definition of PPC's __atomic_op_release().
> > 
> > 
> > But I think removing smp_lwsync() is a good idea and actually I think we
> > can go further to remove __smp_lwsync() and let __smp_load_acquire and
> > __smp_store_release call __lwsync() directly, but that is another thing.
> > 
> > Anyway, I will modify my patch.
> > 
> > Regards,
> > Boqun
> 
> 
> Thanks!
> Could you send an ack then please?
> 

Sure, if you need one from me, feel free to add my ack for this patch:

Acked-by: Boqun Feng <boqun.feng@gmail.com>

Regards,
Boqun

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