Re: [PATCH 0/2] jump label: 2.6.38 updates

[Steven Rostedt]

On Mon, 2011-02-14 at 19:24 +0100, Peter Zijlstra wrote:
> On Mon, 2011-02-14 at 17:50 +0000, Will Newton wrote:
> > 
> > It would observe a stale value, but that value would only be updated
> > when the cache line was reloaded from main memory which would have to
> > be triggered by either eviction or cache flushing. So it could get
> > pretty stale. Whilst that's probably within the spec. of atomic_read I
> > suspect it would lead to problems in practice. I could be wrong
> > though. 
> 
> Right, so the typical scenario that could cause pain is something like:
> 
> while (atomic_read(&foo) != n)
>   cpu_relax();
> 
> and the problem is that cpu_relax() doesn't know which particular
> cacheline to flush in order to make things go faster, hm?

But what about any global variable? Can't we also just have:

	while (global != n)
		cpu_relax();

?

-- Steve


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