Re: [patch 2.6.13-rc3a] i386: inline restore_fpu

[Linus Torvalds <torvalds@osdl.org>]

On Thu, 21 Jul 2005, Chuck Ebbert wrote:
> 
>   This patch makes restore_fpu() an inline.  When L1/L2 cache are saturated
> it makes a measurable difference.

I've now pushed out an alternative fix for this, which imho is much 
cleaner.

We've long had infrastructure for "alternative asm instructions" that are 
conditional on CPU features, and I just made restore_fpu() use that 
instead:

	/*
	 * The "nop" is needed to make the instructions the same
	 * length.
	 */
	#define restore_fpu(tsk)                        \
	        alternative_input(                      \
	                "nop ; frstor %1",              \
	                "fxrstor %1",                   \
	                X86_FEATURE_FXSR,               \
	                "m" ((tsk)->thread.i387.fsave))

which not only makes it inline, but makes it a single instruction instead 
of the mess it was before.

Now, we should do the same for "fnsave ; fwait" vs "fxsave ; fnclex" too,
but I was lazy. If somebody wants to try that, it would need an 
"alternative_output()" define but should otherwise be trivial too.

		Linus
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