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@xxxxxxxxxx>
> > Acked-by: Arnd Bergmann <arnd@xxxxxxxx>
> > ---
> > 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
> >
> > --
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