On Fri, Jul 27, 2012 at 10:28:25AM +0100, Ian Campbell wrote: > On Thu, 2012-07-26 at 17:37 +0100, Konrad Rzeszutek Wilk wrote: > > On Thu, Jul 26, 2012 at 04:33:46PM +0100, Stefano Stabellini wrote: > > > sync_bitops functions are equivalent to the SMP implementation of the > > > original functions, independently from CONFIG_SMP being defined. > > > > So why can't the code be changed to use that? Is it that > > the _set_bit, _clear_bit, etc are not available with !CONFIG_SMP? > > _set_bit etc are not SMP safe if !CONFIG_SMP. But under Xen you might be > communicating with a completely external entity who might be on another > CPU (e.g. two uniprocessor guests communicating via event channels and > grant tables). So we need a variant of the bit ops which are SMP safe > even on a UP kernel. > > The users are common code and the sync_foo vs foo distinction matters on > some platforms (e.g. x86 where a UP kernel would omit the LOCK prefix > for the normal ones).
OK, that makes sense. Stefano can you include that comment in the git commit description and in the sync_bitops.h file please? > > > > > > > > > Signed-off-by: Stefano Stabellini <stefano.stabell...@eu.citrix.com> > > > --- > > > arch/arm/include/asm/sync_bitops.h | 17 +++++++++++++++++ > > > 1 files changed, 17 insertions(+), 0 deletions(-) > > > create mode 100644 arch/arm/include/asm/sync_bitops.h > > > > > > diff --git a/arch/arm/include/asm/sync_bitops.h > > > b/arch/arm/include/asm/sync_bitops.h > > > new file mode 100644 > > > index 0000000..d975092903 > > > --- /dev/null > > > +++ b/arch/arm/include/asm/sync_bitops.h > > > @@ -0,0 +1,17 @@ > > > +#ifndef __ASM_SYNC_BITOPS_H__ > > > +#define __ASM_SYNC_BITOPS_H__ > > > + > > > +#include <asm/bitops.h> > > > +#include <asm/system.h> > > > + > > > +#define sync_set_bit(nr, p) _set_bit(nr, p) > > > +#define sync_clear_bit(nr, p) _clear_bit(nr, p) > > > +#define sync_change_bit(nr, p) _change_bit(nr, p) > > > +#define sync_test_and_set_bit(nr, p) _test_and_set_bit(nr, p) > > > +#define sync_test_and_clear_bit(nr, p) _test_and_clear_bit(nr, p) > > > +#define sync_test_and_change_bit(nr, p) _test_and_change_bit(nr, p) > > > +#define sync_test_bit(nr, addr) test_bit(nr, addr) > > > +#define sync_cmpxchg cmpxchg > > > + > > > + > > > +#endif > > > -- > > > 1.7.2.5 > > > > > > > > > _______________________________________________ > > > Xen-devel mailing list > > > xen-de...@lists.xen.org > > > http://lists.xen.org/xen-devel > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
