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

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Date:	Mon, 16 Feb 2015 19:14:17 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Rik van Riel <riel@...hat.com>
Cc:	Borislav Petkov <bp@...en8.de>, 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

On 02/16, Rik van Riel wrote:
>
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> 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.

And to me, thanks.

Should I resend?

Oleg.

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