linux-kernel - Re: [PATCH 2/3] x86, fpu: always allow FPU in interrupt if use_eager

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Message-ID: <54BE6A41.5030004@redhat.com>
Date:	Tue, 20 Jan 2015 09:46:25 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Oleg Nesterov <oleg@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Suresh Siddha <sbsiddha@...il.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: [PATCH 2/3] x86, fpu: always allow FPU in interrupt if use_eager_fpu()

On 01/19/2015 01:51 PM, Oleg Nesterov wrote:
> The __thread_has_fpu() check in interrupted_kernel_fpu_idle() was needed
> to prevent the nested kernel_fpu_begin(). Now that we have in_kernel_fpu
> and !__thread_has_fpu() case in __kernel_fpu_begin() does not depend on
> use_eager_fpu() (except clts) we can remove it.
>
> __thread_has_fpu() can be false even if use_eager_fpu(), but this case
> does not differ from !use_eager_fpu() case except we should not worry
> about X86_CR0_TS, __kernel_fpu_begin/end will not touch this bit.
>
> Note: I think we can kill all irq_fpu_usable() checks except in_kernel_fpu,
> just we need to record the state of X86_CR0_TS in __kernel_fpu_begin() and
> conditionalize stts() in __kernel_fpu_end(), but this needs another patch.
>
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>

Reviewed-by: Rik van Riel <riel@...hat.com>

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