Re: [PATCH] move xchg/cmpxchg to atomic.h

[Daniel Phillips <phillips@innominate.de>]

Roman Zippel wrote:
> 
> On Tue, 2 Jan 2001, David S. Miller wrote:
> 
> >    We really can't.  We _only_ have load-and-zero.  And it has to be
> >    16-byte aligned.  xchg() is just not something the CPU implements.
> >
> > Oh bugger... you do have real problems.
> 
> For 2.5 we could move all the atomic functions from atomic.h, bitops.h,
> system.h and give them a common interface. We could also give them a new
> argument atomic_spinlock_t, which is a normal spinlock, but only used on
> architectures which need it, everyone else can "optimize" it away. I think
> one such lock per major subsystem should be enough, as the lock is only
> held for a very short time, so contentation should be no problem.
> Anyway, this had the huge advantage that we could use the complete 32/64
> bit of the atomic value, e.g. for pointer operations.

*Yes*, and I could write:
	waiters = xchg(&bdflush_waiters.counter, 0);

instead of:
        waiters = atomic_read(&bdflush_waiters);
        atomic_sub(waiters, &bdflush_waiters);

in my daemon wakeup patch.

--
Daniel
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