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

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Message-ID: <20080224162932.GB27194@linux-os.sc.intel.com>
Date:	Sun, 24 Feb 2008 08:29:32 -0800
From:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>
To:	Roger While <simrw@...-basis.de>
Cc:	linux-kernel@...r.kernel.org, suresh.b.siddha@...el.com
Subject: Re: [patch 1/2] x86,fpu: split FPU state from task struct

On Sun, Feb 24, 2008 at 08:27:30AM +0100, Roger While wrote:
> 
> On Sat, Feb 23, 2008 at 06:34:38PM -0800, Suresh Siddha wrote:
> > Split the FPU save area from the task struct. This allows easy migration
> > of FPU context, and it's generally cleaner. It also allows the following
> > two optimizations:
> >
> > 1) only allocate when the application actually uses FPU, so in the first
> > lazy FPU trap. This could save memory for non-fpu using apps. Next patch
> > does this lazy allocation.
> >
> > 2) allocate the right size for the actual cpu rather than 512 bytes 
> always.
> > Patches enabling xsave/xrstor support (coming shortly) will take advantage
> > of this.
> 
> >  	if (next_p->fpu_counter>5)
> > -		prefetch(&next->i387.fxsave);
> > +		prefetch(FXSAVE(next_p));
> 
> Shouldn't that be  prefetch(FXSAVE(next));  ?

No. 'next_p' which is the task_struct is what FXSAVE macro takes.

thanks,
suresh
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