On Wed, 1 Aug 2012, Konrad Rzeszutek Wilk wrote:

On Fri, Jul 27, 2012 at 10:28:25AM +0100, Ian Campbell wrote:

quoted

On Thu, 2012-07-26 at 17:37 +0100, Konrad Rzeszutek Wilk wrote:

quoted

On Thu, Jul 26, 2012 at 04:33:46PM +0100, Stefano Stabellini wrote:

quoted

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?

Yep, I'll do that.