Re: [PATCH 2/2] amd: uncore: Get correct number of cores sharing last level cache

[Peter Zijlstra]

On Mon, Jun 05, 2017 at 11:13:19AM -0500, Janakarajan Natarajan wrote:
> +             /*
> +              * Iterate over Cache Topology Definition leaves until no
> +              * more cache descriptions are available
> +              */
> +             while (1) {
> +                     cpuid_count(0x8000001d, cache_level,
> +                                 &eax, &ebx, &ecx, &edx);
> +                     /*
> +                      * EAX[0:4] gives type of cache. 0 = No more caches
> +                      */
> +                     if ((eax & 0x1f) == 0)
> +                             break;
> +                     cache_level++;
> +                     prev_eax = eax;
> +             }
> +             nshared = ((prev_eax >> 14) & 0xfff) + 1;

Egads, could we pretty please write that in a less horrible fashion?

Maybe something like:

        for (cache_level = 0; cache_level < 3; cache_level++) {
                cpuid_count(0x8000001d, cache_level, &eax, &ebx, &ecx, &edx);

                if ((eax & 0x1f) == 0) /* EAX[0:4] gives cache type */
                        break;

                prev_eax = eax;
        }

That way we'll not run off into the woods if CPUID goes funny (never
trust a BIOS/virt monkey).