linux-kernel - Re: [RFC PATCH] x86, fpu: Use eagerfpu by default on all CPUs

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Message-ID: <20150223184052.GA21067@redhat.com>
Date:	Mon, 23 Feb 2015 19:40:52 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Rik van Riel <riel@...hat.com>
Cc:	Borislav Petkov <bp@...en8.de>,
	Andy Lutomirski <luto@...capital.net>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] x86, fpu: Use eagerfpu by default on all CPUs

On 02/23, Rik van Riel wrote:
>
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> On 02/23/2015 10:11 AM, Borislav Petkov wrote:
> > On Mon, Feb 23, 2015 at 03:59:29PM +0100, Oleg Nesterov wrote:
> >> Well, but if we want this change then perhaps we should simply
> >> change the default value? This way "AUTO" still can work.
> >
> > Yeah, sure, let's do some measurements first, to see whether this
> > is even worth it.
> >
> > Btw, Mel pointed me at some cleanups he did a while ago in that
> > area too: https://lkml.org/lkml/2014/8/6/201
> >
> > If you guys could take a look, that would be awesome :)
>
> I don't think any of those changes would survive the
> "defer FPU loading to do_notify_resume" patch series.

Agreed, at least

	+static inline void switch_eagerfpu_prepare(struct task_struct *old, struct task_struct *new, int cpu,
	+						fpu_switch_t *fpu)
	+{
	+	fpu->preload = tsk_used_math(new);

doesn't look right if we change the rules.

OTOH, perhaps it makes sense to redo these cleanups later.

Oleg.

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