Re: [PATCH 4/4] perf, tools: Add perf stat --transaction v3

[Andi Kleen <andi@firstfloor.org>]

> > +/* Default events used for perf stat -T */
> > +static const char * const transaction_attrs[] = {
> > +	"task-clock",
> > +	"{"
> > +	"instructions,"
> > +	"cycles,"
> > +	"cpu/cycles-t/,"
> > +	"cpu/tx-start/,"
> > +	"cpu/el-start/,"
> > +	"cpu/cycles-ct/"
> > +	"}"
> > +};
> > +
> > +/* More limited version when the CPU does not have all events. */
> > +static const char * const transaction_limited_attrs[] = {
> > +	"task-clock",
> > +	"{"
> > +	"instructions,"
> > +	"cycles,"
> > +	"cpu/cycles-t/,"
> > +	"cpu/tx-start/"
> > +	"}"
> > +};
> > +
> > +/* must match the transaction_attrs above */
> 
> Match in what way? It kinda matches the first one (transaction_attrs):

The second is just the beginning of the first.

The { } don't count for matches.

For the limited run the comparisons of the elements that are not there
fail.

> 
> enum {
> 	T_TASK_CLOCK,        ==	"task-clock",
> 	T_INSTRUCTIONS,      == "instructions,"
> 	T_CYCLES,	     == "cycles,"
> 	T_CYCLES_IN_TX,      ~= "cpu/cycles-t/,"
> 	T_TRANSACTION_START, != "cpu/tx-start/,"
> 	T_ELISION_START,     ~= "cpu/el-start/,"
> 	T_CYCLES_IN_TX_CP,   != "cpu/cycles-ct/"
> };

I did a quick test of the fallback path by manually disabling the events,
and it seemed to work, but it's really for POWER based on Michael E's feedback.

> 
> Also the enum numbers won't match the array positions due to the '{'
> grouping (?) entries, so, without looking further, how can this match?
> Reading on...

The match is on the result array.  The results don't contain the { } 
as individual elements.

Anyways I use this option pretty heavily and the results are good
to my knowledge.

-Andi