linux-kernel - Re: [PATCH 1/8] x86, fpu: unlazy_fpu: don't reset thread.fpu

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Message-ID: <54E22FCD.3030202@redhat.com>
Date:	Mon, 16 Feb 2015 12:58:37 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Borislav Petkov <bp@...en8.de>, oleg@...hat.com
CC:	dave.hansen@...ux.intel.com, sbsiddha@...il.com,
	luto@...capital.net, tglx@...utronix.de, mingo@...nel.org,
	hpa@...or.com, fenghua.yu@...el.com, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/8] x86, fpu: unlazy_fpu: don't reset thread.fpu_counter

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On 02/16/2015 12:04 PM, Borislav Petkov wrote:

> ... and so by looking at the unlazy_fpu() call sites, I think this
> makes sense.
> 
> So how's that for a commit message instead:
> 
> --- x86, fpu, unlazy_fpu: Don't reset thread.fpu_counter
> 
> The "else" branch clears ->fpu_counter as a remnant of the lazy
> FPU usage counting:
> 
> e07e23e1fd30 ("[PATCH] non lazy "sleazy" fpu implementation")
> 
> However, switch_fpu_prepare() does this now so that else branch is 
> superfluous.
> 
> If we do use_eager_fpu(), then this has no effect. Otherwise, if
> we actually wanted to prevent fpu preload after the context switch
> we would need to reset it unconditionally, even if
> __thread_has_fpu(). ---
> 
> ?

Good detective work.

Your changelog makes sense to me.

- -- 
All rights reversed
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