Re: [RFC] New locking primitive for 2.5

[Daniel Phillips <phillips@bonn-fries.net>]

On February 7, 2002 07:22 pm, Christoph Hellwig wrote:
> In article <3C629F91.2869CB1F@dlr.de> you wrote:
> > If a spin_lock request is blocked by a mutex_lock call, the spin_lock
> > attempt also sleeps i.e. behaves like a semaphore.
> > If you gained ownership of the lock, you can switch between spin-mode
> > and mutex-(ie.e sleeping) mode by calling:
> >
> >         combi_to_mutex_mode(struct combilock *x)
> >         combi_to_spin_mode(struct combilock *x)
> >
> > without loosing the lock. So you may start with a spin-lock and relax
> > to a sleeping lock if for example you need to call a non-atomic kmalloc.
> 
> This looks really ugly.  I'd really prefer an automatic fallback from
> spinning to sleeping after some timeout like e.g. solaris adaptive
> mutices.

Look closer at what he said.  You'd take the lock, then you might decide you
had to do something on a slow/blocking path, for example, a copy to/from user,
so you could do that without leaving waiters spinning, or having to
acquire a different lock and re-establish the state.  It bears thinking
about.

-- 
Daniel