linux-kernel - Re: [PATCH 8/9] perf,tools: caculate and save tsc/avg/bzy freq in he

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Date:	Fri, 17 Jul 2015 13:25:53 -0700
From:	Andi Kleen <ak@...ux.intel.com>
To:	kan.liang@...el.com
Cc:	a.p.zijlstra@...llo.nl, mingo@...hat.com, acme@...nel.org,
	eranian@...gle.com, mark.rutland@....com, adrian.hunter@...el.com,
	dsahern@...il.com, jolsa@...nel.org, namhyung@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 8/9] perf,tools: caculate and save tsc/avg/bzy freq in
 he_stat

> +	if (sample->read.time_running > 0) {
> +		freq.tsc_freq = (1000 * sample->tsc) / sample->read.time_running;
> +		freq.avg_freq = (1000 * sample->aperf) / sample->read.time_running;
> +		if (sample->aperf > 0)
> +			freq.bzy_freq = freq.tsc_freq * sample->mperf / sample->aperf;

Sorry didn't notice that earlier. The formula is not correct. 
aperf/mperf is not necessarily the frequency, it is essentially a load average
of the CPU. It should be reported as such. Also only the ratio is
architecturally defined.

The right way to compute frequency is cycles / ref-cycles
TSC can be used to accurately compute CPU utilization tsc / ref-cycles

It would be useful to report all three metrics.

-Andi
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