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

[Peter Zijlstra]

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?



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