Re: [PATCH V5 5/6] x86/intel_rdt: Use perf infrastructure for measurements

[Peter Zijlstra]

On Wed, Sep 19, 2018 at 10:29:10AM -0700, Reinette Chatre wrote:
> +static int measure_l3_residency(void *_plr)
> +{

> +     counts.miss_after -= counts.miss_before;
> +     if (boot_cpu_data.x86_model == INTEL_FAM6_BROADWELL_X) {
> +             /*
> +              * On BDW references and misses are counted, need to adjust.
> +              * Sometimes the "hits" counter is a bit more than the
> +              * references, for example, x references but x + 1 hits.
> +              * To not report invalid hit values in this case we treat
> +              * that as misses equal to references.
> +              */
> +             /* First compute the number of cache references measured */
> +             counts.hits_after -= counts.hits_before;

> +             /* Next convert references to cache hits */
> +             counts.hits_after -= counts.miss_after > counts.hits_after ?
> +                                     counts.hits_after : counts.miss_after;

Maybe:
                counts.hits_after -= min(counts.hits_after, counts.miss_after);