Re: [PATCH 1/2] x86/mce: Pack boolean MCE boot flags into a structure

[Naveen N. Rao]

On 08/27/2012 07:48 PM, Borislav Petkov wrote:
> On Mon, Aug 27, 2012 at 03:58:59PM +0200, Andi Kleen wrote:
> > On Mon, Aug 27, 2012 at 04:55:03PM +0530, Naveen N. Rao wrote:
> > > Many MCE boot flags are boolean in nature, but are declared as integers
> > > currently. We can pack these into a bitfield to save some space.
> >
> > Note that this doesn't necessarily save anything because it needs more
> > code to access, and accesses are more common than the flag
> >
> > 	cmpl  $0,foo(%rip)            7 bytes
> >          testl $1,foo(%rip)           10 bytes
>
> I got 7 bytes:
>
> 12e9:       f6 05 00 00 00 00 02    testb  $0x2,0x0(%rip)        # 12f0 <mce_start_timer.isra.18+0x30>
>
> vs the old:
>
> 1654:       83 3d 00 00 00 00 00    cmpl   $0x0,0x0(%rip)        # 165b <mce_start_timer.clone.15+0x37>
>
> also 7 bytes.

I'm seeing the same here. GCC v4.7 with -O2 generates testb and cmpb, 
which are both 7 bytes long.

Thanks,
Naveen

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