linux-kernel - Re: [PATCH RFC 4/5] x86,fpu: lazily skip FPU restore when still loaded

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Message-ID: <1475528577.4622.11.camel@redhat.com>
Date:   Mon, 03 Oct 2016 17:02:57 -0400
From:   Rik van Riel <riel@...hat.com>
To:     Dave Hansen <dave.hansen@...ux.intel.com>,
        linux-kernel@...r.kernel.org
Cc:     x86@...nel.org, tglx@...utronix.de, pbonzini@...hat.com,
        mingo@...hat.com, luto@...nel.org, hpa@...or.com, bp@...e.de
Subject: Re: [PATCH RFC 4/5] x86,fpu: lazily skip FPU restore when still
 loaded

On Mon, 2016-10-03 at 13:49 -0700, Dave Hansen wrote:
> On 10/03/2016 01:22 PM, Rik van Riel wrote:
> > 
> > > 
> > > > 
> > > > What are the preempt rules with this thing?  This needs to be
> > > > called
> > > > in preempt-disabled contexts, right?
> > Indeed, all the FPU context switching code needs 
> > to be called in preempt-disabled contexts.
> > 
> > You do not want to get preempted halfway through
> > saving or restoring floating point registers.
> OK, cool, that's what I expected.  Could you just add a comment about
> it
> to make it clear that it's also the case for this new
> fpu_lazy_skip_restore() helper?

Turns out the code already has an old
fpu_want_lazy_restore(), which is what
I will use instead :)

I will add documentation about preemption
in places where it is necessary.

-- 
All rights reversed

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