On Mon, Jun 14, 2010 at 06:51:30PM +0200, Paolo Bonzini wrote:
> On 06/14/2010 02:41 AM, Paul E. McKenney wrote:
> >The compiler (and sometimes the CPU) are within their rights to move
> >code into a lock-based critical section. With two
> >locks:
> >
> > do_first_thing();
> > acquire_lock();
> > release_lock();
> > acquire_lock();
> > release_lock();
> > do_second_thing();
> >
> >the worst that the compiler and CPU can do is:
> >
> > acquire_lock();
> > do_first_thing();
> > release_lock();
> > acquire_lock();
> > do_second_thing();
> > release_lock();
> >
> >which is still acting like a memory barrier.
>
> Interesting, so it's actually the release+acquire that is doing the
> job. I thought about barrier+acquire+release+barrier, but that
> would placate the compiler only, not the CPU.
Strange but true! ;-)
Thanx, Paul
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