Re: [PATCH] remove LOCK_SECTION from x86_64 spin_lock asm

[Ingo Molnar]

* Andi Kleen <ak@xxxxxxx> wrote:

> > the alternative would be to unwind the stack - quite some task on some 
> > platforms ...
> 
> Sometimes call graph profiling would be very useful, but I wouldn't
> want the profiler to do it by default, especially not for this silly
> simple case. dwarf2 unwinding is complex enough that just requiring
> frame pointers for the CG case would look attractive.

but ... frame pointers are overhead to all of the kernel. (the overhead
is less pronounced on architectures with more registers, but even with
15 registers, 14 or 15 can still be a difference.) While unwinding is
overhead to profiling only - if enabled. Also, there could be other
functionality (exception handling?) that could benefit from dwarf2
unwinding.

	Ingo
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