RE: [PATCH 00/12] Cqm2: Intel Cache quality monitoring fixes

[Luck, Tony]

>> Nice to have:
>> 1)      Readout using "perf(1)" [subset of modes that make sense ... tying monitoring
>> to resctrl file system will make most command line usage of perf(1) close to impossible.
>
>
> We discussed this offline and I still disagree that it is close to
> impossible to use perf and perf_event_open. In fact, I think it's very
> simple :

Maybe s/most/many/ ?

The issue here is that we are going to define which tasks and cpus are being
monitored *outside* of the perf command.  So usage like:

# perf stat -I 1000 -e intel_cqm/llc_occupancy {command}

are completely out of scope ... we aren't planning to change the perf(1)
command to know about creating a CQM monitor group, assigning the
PID of {command} to it, and then report on llc_occupancy.

So perf(1) usage is only going to support modes where it attaches to some
monitor group that was previously established.  The "-C 2" option to monitor
CPU 2 is certainly plausible ... assuming you set up a monitor group to track
what is happening on CPU 2 ... I just don't know how perf(1) would know the
name of that group.

Vikas is pushing for "-R rdtgroup" ... though our offline discussions included
overloading "-g" and have perf(1) pick appropriately from cgroups or rdtgroups
depending on event type.

-Tony