linux-kernel - Re: [patch 1/2] x86, fpu: split FPU state from task struct

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Message-ID: <20080311101126.GY25110@elte.hu>
Date:	Tue, 11 Mar 2008 11:11:26 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Alexey Dobriyan <adobriyan@...il.com>
Cc:	Suresh Siddha <suresh.b.siddha@...el.com>, hpa@...or.com,
	tglx@...utronix.de, andi@...stfloor.org, hch@...radead.org,
	linux-kernel@...r.kernel.org,
	Arjan van de Ven <arjan@...ux.intel.com>
Subject: Re: [patch 1/2] x86, fpu: split FPU state from task struct - v5


* Alexey Dobriyan <adobriyan@...il.com> wrote:

> On 3/11/08, Ingo Molnar <mingo@...e.hu> wrote:
> >
> > * Alexey Dobriyan <adobriyan@...il.com> wrote:
> >
> > > > -	extern void __bad_fxsave_alignment(void);
> > > > -
> > > > -	if (offsetof(struct task_struct, thread.i387.fxsave) & 15)
> > > > -	__bad_fxsave_alignment();
> > >
> > > I think removal of such checks needs giving necessary alignment to
> > > cache. Previously it worked because of __aligned((16)) and
> > > L1_CACHE_SHIFT combo.
> >
> > it's still checked, just elsewhere:
> >
> > > + WARN_ON((unsigned long)dst->thread.xstate & 15);
> >
> > i'd not expect us to ever align worse than 16 bytes in the future
> 
> But sysfs tells me alignment of "xstate" is 8 now. Object size is 512 
> which is masking it.

ok - you are right, that needs to be solved then. (object size could 
change anytime someone adds a few fields for debugging or whatever)

	Ingo
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