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Message-ID: <8763kqxs2p.fsf@basil.nowhere.org> Date: Thu, 08 Jan 2009 06:52:30 +0100 From: Andi Kleen <andi@...stfloor.org> To: Alan Cox <alan@...rguk.ukuu.org.uk> Cc: Om <om.turyx@...il.com>, linux-kernel@...r.kernel.org Subject: Re: 64 bit PCI access using MMX register -- how? Alan Cox <alan@...rguk.ukuu.org.uk> writes: > One other problem: the kernel doesn't save the FPU state on context > switches or IRQ entry (takes far too long) so that will make a nasty mess. I think he was ok because he saved the MMX state by itself, except: - There was no guarantee that the FPU is in MMX state, not x87 state - He'll often get a lazy fpu save exception. This used to BUG() in some cases when invoked from kernel space (but that might have been changed now). Better is to disable this explicitely around the access (like in kernel_fpu_begin()/end()) - Doing this all properly is fairly expensive and I suspect just using a lock will be cheaper. -Andi -- ak@...ux.intel.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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