Speaking from the user's seat. An optional (not just empty) cgroup
field is fine as long it consistently appears when requested with -G
option. The problem with print_metric_csv() was that in the case of
unsupported counters 2 additional empty fields in the output are
completely unexpected and not documented anywhere.

Andi, in the output example in your commit
92a61f6412d3a09d6462252a522fa79c9290f405 stalled-cycles-backend event
has counter run time field, counter run time percentage field, empty
metric value, empty metric unit, and then 2 other empty fields. Are
they expected? If yes, what are they and why other events, e.g.
stalled-cycles-frontend, don't have them? Am I missing something here?

On Tue, Mar 6, 2018 at 11:03 AM, Cong Wang <xiyou.wangc...@gmail.com> wrote:
> On Tue, Mar 6, 2018 at 9:53 AM, Andi Kleen <a...@linux.intel.com> wrote:
>>> Here is the output from your own commit:
>>>       423470,,stalled-cycles-frontend,509102,100.00,65.69,frontend cycles 
>>> idle
>>>       <not supported>,,stalled-cycles-backend,0,100.00,,,,
>>> so line 1 has 7 fields, line 2 has 9 fields, and this is expected?
>> If you had metrics on line 1 it would be correct.
>> So you just shifted it to break that case.
>> If you always want to have the same number of fields
>> you need to add two empty fields to the normal output
>> when there are no metrics.
> The number of separators is the only way to learn the number
> of fields, therefore it must be a fixed number.
> Yeah, it could be the other way that supported ones have less
> separators than it should. If we look at print_metric_csv() alone,
> it should produce a same number of separators for all cases,
> otherwise hard to count.
> So I believe we need an additional patch, like the one attached,
> to make it complete? Note, I only spot the cgroup field here.

Ilya Pronin

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