Re: [PATCH v9 2/5] x86/cpuid: Add generic table for cpuid dependencies

Thomas Gleixner
2017-10-12T15:13:49Z

On Thu, 12 Oct 2017, Ingo Molnar wrote:
>
> * Andi Kleen <andi@firstfloor.org> wrote:
>
> > --- /dev/null
> > +++ b/arch/x86/kernel/cpu/cpuid-deps.c
> > @@ -0,0 +1,109 @@
> > +/* Declare dependencies between CPUIDs */
> > +#include <linux/kernel.h>
> > +#include <linux/init.h>
> > +#include <linux/module.h>
> > +#include <asm/cpufeature.h>
> > +
> > +struct cpuid_dep {
> > + unsigned short feature;
> > + unsigned short depends;
> > +};
>
> Why are these 16-bit fields? 16-bit data types should be avoided as much as
> possible, as they generate suboptimal code.

I was looking at that as well and decided that we preferrably have a
compressed data structure. The code which walks the table is hardly
performance critical and the difference in text size is marginal.

Thanks,

tglx