Re: [PATCH 10/13] perf, tools, stat: Output JSON MetricExpr metric

[Jiri Olsa]

On Mon, Mar 20, 2017 at 01:17:08PM -0700, Andi Kleen wrote:
> From: Andi Kleen <ak@xxxxxxxxxxxxxxx>
> 
> Add generic infrastructure to perf stat to output ratios for "MetricExpr"
> entries in the event lists. Many events are more useful as ratios
> than in raw form, typically some count in relation to total ticks.
> 
> Transfer the MetricExpr information from the alias to the evsel.
> 
> We mark the events that need to be collected for MetricExpr, and also
> link the events using them with a pointer. The code is careful
> to always prefer the right event in the same group to minimize
> multiplexing errors. At the moment only a single relation is supported.
> 
> Then add a rblist to the stat shadow code that remembers stats based
> on the cpu and context.
> 
> Then finally update and retrieve and print these values similarly to the
> existing hardcoded perf metrics. We use the simple expression parser
> added earlier to evaluate the expression.
> 
> Normally we just output the result without further commentary,
> but for --metric-only this would lead to empty columns. So for this
> case use the original event as description.
> 
> There is no attempt to automatically add the MetricExpr event,
> if it is missing, however we suggest it to the user, because
> the user tool doesn't have enough information to reliably
> construct a group that is guaranteed to schedule. So we leave
> that to the user.
> 
> % perf stat -a -I 1000 -e '{unc_p_clockticks,unc_p_freq_max_os_cycles}'
>      1.000147889        800,085,181      unc_p_clockticks
>      1.000147889         93,126,241      unc_p_freq_max_os_cycles  #     11.6
>      2.000448381        800,218,217      unc_p_clockticks
>      2.000448381        142,516,095      unc_p_freq_max_os_cycles  #     17.8
>      3.000639852        800,243,057      unc_p_clockticks
>      3.000639852        162,292,689      unc_p_freq_max_os_cycles  #     20.3
> 
> % perf stat -a -I 1000 -e '{unc_p_clockticks,unc_p_freq_max_os_cycles}' --metric-only
>      1.000127077      0.9
>      2.000301436      0.7
>      3.000456379      0.0

The comment above suggest I'll see 'original event as description' in this example??

jirka