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

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Date:	Mon, 25 Apr 2016 11:13:11 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vikas Shivappa <vikas.shivappa@...ux.intel.com>
Cc:	tony.luck@...el.com, ravi.v.shankar@...el.com,
	fenghua.yu@...el.com, vikas.shivappa@...el.com, x86@...nel.org,
	linux-kernel@...r.kernel.org, hpa@...or.com, tglx@...utronix.de,
	mingo@...nel.org, h.peter.anvin@...el.com
Subject: Re: [PATCH 2/4] perf/x86/mbm: Store bytes counted for mbm during
 recycle

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;