x86 PCU

[Thor Lancelot Simon <tls%panix.com@localhost>]

About 3 years ago Matthias Drochner committed changes to use the MI pcu
framework for lazy FPU switch on x86.

This was quickly backed out by Christos because, evidently, it caused
system hangs.

I am implementing AESNI support as well as some other code that wants
"FPU" registers in the kernel, and I am cringing every time I type in
code that manually saves and restores the FPU state at a cost of hundreds
of cycles per.  So I would love to see PCU working on x86.

I can't find much discussion of what was wrong -- aside from the commit
message when the code was backed out, saying it had caused hangs.  Does
anyone remember or know more about this?  Would anyone be willing to have
another shot at making it go?

-- 
 Thor Lancelot Simon	                                      tls%panix.com@localhost

	Cry, the beloved country, for the unborn child that is the
	inheritor of our fear.			-Alan Paton