Re: [Qemu-devel] [SeaBIOS PATCH 2/2] allow CPUs to have non-contiguous Local APIC IDs (v2)

[Eduardo Habkost]

On Thu, Jul 26, 2012 at 05:55:09PM +0300, Avi Kivity wrote:
> On 07/26/2012 05:16 PM, Eduardo Habkost wrote:
> >> > 
> >> > It's possible to replace the atomic read of CountCPUs with the bitmap 
> >> > weight
> >> > calculation on the loop, but: is it really worth it?
> >> > 
> >> Why not? This eliminates one more global state.
> > 
> > Maybe we can simply make it stop being global and be used only by the
> > smp.c initialization code?
> > 
> > Even if the variable didn't exist yet, I think I would add it myself:
> > it's simpler and more efficient to calculate the bitmap weight once,
> > while filling the bitmap, than recalculating it every time on the
> > while(cmos_smp_count) loop.
> 
> So you're spinning more efficiently?

No, coding more efficiently. I'm lazy. :-)

I don't want to risk breaking that part of the code to save 2 bytes of
memory. It's possible to impement it reliably, yes, but it's also very
easy to introduce a subtle bug, so why touch something that works
perfectly just to save 2 bytes?

-- 
Eduardo