Re: Synchronizing Bit operations V2

[Nick Piggin]

Chen, Kenneth W wrote:
> Christoph Lameter wrote on Thursday, March 30, 2006 6:38 PM
>
> > > > Neither one is correct because there will always be one combination of 
> > > > clear_bit with these macros that does not generate the required memory 
> > > > barrier.
> > >
> > > Can you give an example?  Which combination?
> >
> > For Option(1)
> >
> > smp_mb__before_clear_bit()
> > clear_bit(...)(
>
>
> Sorry, you totally lost me.  It could me I'm extremely slow today.  For
> option (1), on ia64, clear_bit has release semantic already.  The comb
> of __before_clear_bit + clear_bit provides the required ordering.  Did
> I miss something?  By the way, we are talking about detail implementation
> on one specific architecture.  Not some generic concept that clear_bit
> has no ordering stuff in there.

The memory ordering that above combination should produce is a
Linux style smp_mb before the clear_bit. Not a release.

--
SUSE Labs, Novell Inc.
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