Re: SMP syncronization on AMD processors (broken?)

[Hugh Dickins <hugh@veritas.com>]

On Thu, 6 Oct 2005, Linus Torvalds wrote:
> 
> If you want to notify another CPU that you want the spinlock, then you 
> need to set the "flag" variable _outside_ of the spinlock.
> 
> Spinlocks are not fair, not by a long shot. They never have been, and they 
> never will. Fairness would be extremely expensive indeed.

That reminds me: ought cond_resched_lock to be doing something more?

int cond_resched_lock(spinlock_t *lock)
{
	int ret = 0;

	if (need_lockbreak(lock)) {
		spin_unlock(lock);
		cpu_relax();
		ret = 1;
		spin_lock(lock);
	}