svn commit: r202889 - head/sys/kern

[Marcel Moolenaar]

On Jan 26, 2010, at 12:09 PM, M. Warner Losh wrote:
> cpu_switch(struct thread *old, struct thread *new, struct mutext *mtx)
> {
> 	/* Save the registers to the pcb */
> 	old->td_lock = mtx;
> #if defined(SMP) && defined(SCHED_ULE)
> 	/* s/long/int/ if sizeof(long) != sizeof(void *) */
> 	/* as we have no 'void *' version of the atomics */
> 	while (atomic_load_acq_long(&new->td_lock) == (long)&blocked_lock)
> 		continue;
> #endif
> 	/* Switch to new context */
> }

Ok. So this is what ia64 has already, except for the atomic_load()
in the while loop. Since td_lock is volatile, I don't think we need
atomic_load(). To be explicit, ia64 has:

		old->td_lock = mtx;
#if defined(SCHED_ULE) && defined(SMP)
		/* td_lock is volatile */
		while (new->td_lock == &blocked_lock)
			;
#endif

Am I right, or am I missing a critical aspect of using atomic load?

> I also think that we should have that code somewhere for reference.

Since ia64 has a C implementation of cpu_switch(), we could make
that the reference implementation?

-- 
Marcel Moolenaar
xcllnt at mac.com