Re: [beta patch] SSE copy_page() / clear_page()

[Manfred Spraul <manfred@colorfullife.com>]

Manfred Spraul wrote:
> 
> copy_*_user is probably not worth the effort for a Pentium III, but even
> for that function I don't see a problem with SSE, as long as
>
> * the clobbered registers are stored on the stack (and not in
>   thread.i387.fxsave)
> * the SSE/SSE2 instructions can't cause SIMD exceptions.
> * noone saves the fpu state into thread.i387.fxsave from interrupts /
> softirq's. Currently it's impossible, but I haven't checked Montavista's
> preemptive kernel scheduler.
>
I overlooked one restriction:
* you must not schedule() with the "wrong" sse registers: switch_to()
saves into i387.fxsave.

This means that copy_*_user isn't that simple.

--
	Manfred
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