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 20:57:36 +0000
From:	"Liang, Kan" <kan.liang@...el.com>
To:	Andi Kleen <ak@...ux.intel.com>
CC:	"a.p.zijlstra@...llo.nl" <a.p.zijlstra@...llo.nl>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"acme@...nel.org" <acme@...nel.org>,
	"eranian@...gle.com" <eranian@...gle.com>,
	"mark.rutland@....com" <mark.rutland@....com>,
	"Hunter, Adrian" <adrian.hunter@...el.com>,
	"dsahern@...il.com" <dsahern@...il.com>,
	"jolsa@...nel.org" <jolsa@...nel.org>,
	"namhyung@...nel.org" <namhyung@...nel.org>,
	"linux-kernel@...r.kernel.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 concept of tsc, avg and bzy are from turbostat.
Here is the definition from turbostat readme.
- AVG_MHz = APERF_delta/measurement_interval.  This is the actual
  number of elapsed cycles divided by the entire sample interval
- TSC_MHz = TSC_delta/measurement_interval.
  On a system with an invariant TSC, this value will be constant
  and will closely match the base frequency value
- Bzy_MHz = TSC_delta/APERF_delta/MPERF_delta/measurement_interval
  
Only the Bzy_MHz is wrong and has a typo error.
Other formula should be correct. 

If it's confusion, I will change the name and make it consistent as turbostat.

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

I think I can add the support for frequency and CPU% calculation, 
and show them in --stdio.

Thanks,
Kan

> 
> It would be useful to report all three metrics.
> 
> -Andi
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