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Date: Tue, 13 Jan 2015 18:11:34 +0100 From: Oleg Nesterov <oleg@...hat.com> To: riel@...hat.com Cc: linux-kernel@...r.kernel.org, mingo@...hat.com, hpa@...or.com, matt.fleming@...el.com, bp@...e.de, pbonzini@...hat.com, tglx@...utronix.de, luto@...capital.net Subject: Re: [RFC PATCH 04/11] x86,fpu: defer FPU restore until return to userspace On 01/11, riel@...hat.com wrote: > > Defer restoring the FPU state, if so desired, until the task returns to > userspace. And I have another concern. Afaocs with this patch the idle threads will run with TIF_LOAD_FPU set but without fpu.has_fpu. This is fine by itself, but this (performance-wise) breaks kernel_fpu_begin() if use_eager_fpu() == T. Please see the changelog in 5187b28ff08249ab8a162e8 and note that this patch cc's @stable. Yes, yes, even if I am right we should blame kernel_fpu_begin() and other eager_fpu oddities. I tried to start the cleanups/fixes in this area some time ago, but they were ignored. Oleg. -- 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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