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Date: Sat, 10 Feb 2001 19:18:00 +0100
From: Manfred Spraul <manfred@colorfullife.com>
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To: Doug Ledford <dledford@redhat.com>,
        Linus Torvalds <torvalds@transmeta.com>, linux-kernel@vger.kernel.org
Subject: Re: [beta patch] SSE copy_page() / clear_page()
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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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