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

From: Peter Zijlstra
Date: Wed Feb 08 2017 - 06:20:25 EST

On Fri, Jan 20, 2017 at 12:11:53PM -0800, David Carrillo-Cisneros wrote:
> Implementation ideas:
> First idea is to expose one monitoring file per resource in a CTRLGRP,
> so the list of CTRLGRP's files would be: schemata, tasks, cpus,
> monitor_l3_0, monitor_l3_1, ...
> the monitor_<resource_id> file descriptor is passed to perf_event_open
> in the way cgroup file descriptors are passed now. All events to the
> same (CTRLGRP,resource_id) share RMID.
> The RMID allocation part can either be handled by RDT Allocation or by
> the RDT Monitoring PMU. Either ways, the existence of PMU's
> perf_events allocates/releases the RMID.

So I've had complaints about exactly that behaviour. Someone wanted
RMIDs assigned (and start measuring) the moment the grouping got
created/tasks started running etc..

So I think the design should also explicitly state how this is supposed
to be handled and not left as an implementation detail.