Re: [PATCH 2/4] perf/x86/mbm: Store bytes counted for mbm during recycle

[Peter Zijlstra]

On Fri, Apr 22, 2016 at 05:27:19PM -0700, Vikas Shivappa wrote:
> +static inline void mbm_set_rccount(
> +                       struct perf_event *event, struct rmid_read *rr)

That's horrible style, the 'normal' style is something like:

static inline
void mbm_set_rccount(struct perf_event *event, struct rmid_read *rr)
{
}

> @@ -1244,8 +1270,16 @@ static u64 intel_cqm_event_count(struct perf_event 
> *event)
>       cqm_mask_call(&rr);
>  
>       raw_spin_lock_irqsave(&cache_lock, flags);
> -     if (event->hw.cqm_rmid == rr.rmid)
> -             local64_set(&event->count, atomic64_read(&rr.value));
> +     if (event->hw.cqm_rmid == rr.rmid) {
> +             if (is_mbm_event(event->attr.config)) {
> +                     tmpval = atomic64_read(&rr.value) +
> +                             local64_read(&event->hw.rc_count);
> +
> +                     local64_set(&event->count, tmpval);
> +             } else {
> +                     local64_set(&event->count, atomic64_read(&rr.value));
> +             }
> +     }
>       raw_spin_unlock_irqrestore(&cache_lock, flags);
>  out:
>       return __perf_event_count(event);

This is a 'creative' solution; why don't you do the normal thing, which
is:

start:
        prev_count = read_hw_counter();

read:
        do {
                prev = prev_count;
                cur_val = read_hw_counter();
                delta = cur_val - prev;
        } while (local_cmpxchg(&prev_count, prev, cur_val) != prev);
        count += delta;