lkml.org 
[lkml]   [2012]   [Aug]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [Xen-devel] [PATCH 04/24] xen/arm: sync_bitops
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.stabellini@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-devel@lists.xen.org
> > > http://lists.xen.org/xen-devel
>


\
 
 \ /
  Last update: 2012-08-01 17:21    [W:0.099 / U:0.120 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site