On Mon, Jan 04, 2016 at 02:45:25PM +0100, Peter Zijlstra wrote: > On Thu, Dec 31, 2015 at 09:08:38PM +0200, Michael S. Tsirkin wrote: > > This defines __smp_xxx barriers for s390, > > for use by virtualization. > > > > Some smp_xxx barriers are removed as they are > > defined correctly by asm-generic/barriers.h > > > > Note: smp_mb, smp_rmb and smp_wmb are defined as full barriers > > unconditionally on this architecture. > > > > Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx> > > Acked-by: Arnd Bergmann <arnd@xxxxxxxx> > > --- > > arch/s390/include/asm/barrier.h | 15 +++++++++------ > > 1 file changed, 9 insertions(+), 6 deletions(-) > > > > diff --git a/arch/s390/include/asm/barrier.h b/arch/s390/include/asm/barrier.h > > index c358c31..fbd25b2 100644 > > --- a/arch/s390/include/asm/barrier.h > > +++ b/arch/s390/include/asm/barrier.h > > @@ -26,18 +26,21 @@ > > #define wmb() barrier() > > #define dma_rmb() mb() > > #define dma_wmb() mb() > > -#define smp_mb() mb() > > -#define smp_rmb() rmb() > > -#define smp_wmb() wmb() > > - > > -#define smp_store_release(p, v) \ > > +#define __smp_mb() mb() > > +#define __smp_rmb() rmb() > > +#define __smp_wmb() wmb() > > +#define smp_mb() __smp_mb() > > +#define smp_rmb() __smp_rmb() > > +#define smp_wmb() __smp_wmb() > > Why define the smp_*mb() primitives here? Would not the inclusion of > asm-generic/barrier.h do this? No because the generic one is a nop on !SMP, this one isn't. Pls note this patch is just reordering code without making functional changes. And at the moment, on s390 smp_xxx barriers are always non empty. Some of this could be sub-optimal, but since on s390 Linux always runs on a hypervisor, I am not sure it's safe to use the generic version - in other words, it just might be that for s390 smp_ and virt_ barriers must be equivalent. If in fact this turns out to be wrong, I can pick up a patch to change this, but I'd rather make this a patch on top so that my patches are testable just by compiling and comparing the binary. -- MST
