Re: [PATCH 1/2] tracing/function-return-tracer: Make the functionreturn tracer lockless

[Steven Rostedt]

On Thu, 13 Nov 2008, Andi Kleen wrote:

> > So the answer to this is:
> > 
> >   i = index++;
> >   barrier();
> >   write to index i (not index);
> 
> That was my first thought when I wrote the original email,
> but the disadvantage is that barrier() is a big hammer
> that flushes everything and can make the code much worse.
> That is why I suggested local_add_return() instead.

barrier() is a compiler barrier, does nothing with the caches, and is 
quite cheap. We only need a compiler barrier because we are only 
protecting ourselves from things that happen on the current CPU. No other 
devices or other CPUs are involved.

-- Steve

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