linux-kernel - Re: [PATCH v2 3/3] i387: support lazy restore of FPU state

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Date:	Tue, 21 Feb 2012 14:19:35 -0800
From:	Suresh Siddha <suresh.b.siddha@...el.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 3/3] i387: support lazy restore of FPU state

On Tue, 2012-02-21 at 13:57 -0800, Linus Torvalds wrote:
> On Tue, Feb 21, 2012 at 1:54 PM, Suresh Siddha
> <suresh.b.siddha@...el.com> wrote:
> >
> > Reviewing this code, I think we need to set the 'last_cpu' to an invalid
> > number in the fpu_alloc too. Appended is the patch.
> 
> I cleared fpu_counter in copy_thread() instead.

Hmm, didn't pay attention to that patch. Too many patches ;(

> Doing this in fpu_alloc() isn't necessarily a bad idea, though.

yes, I think we should do this in fpu_alloc() or bit more explicitly by
updating 'last_cpu' in copy_thread().

Someone experimenting with removing fpu pre-load may not realize this
subtle issue.

thanks,
suresh




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