Re: [PATCH 0/4] x86: Add Cache QoS Monitoring (CQM) support

From: Tejun Heo
Date: Sat Jan 04 2014 - 11:11:14 EST


On Fri, Jan 03, 2014 at 12:34:41PM -0800, Peter P Waskiewicz Jr wrote:
> The CPU features themselves are relatively straight-forward, but
> the presentation of the data is less straight-forward. Since this
> tracks cache usage and occupancy per process (by swapping Resource
> Monitor IDs, or RMIDs, when processes are rescheduled), perf would
> not be a good fit for this data, which does not report on a
> per-process level. Therefore, a new cgroup subsystem, cacheqos, has
> been added. This operates very similarly to the cpu and cpuacct
> cgroup subsystems, where tasks can be grouped into sub-leaves of the
> root-level cgroup.

I don't really understand why this is implemented as part of cgroup.
There doesn't seem to be anything which requires cgroup. Wouldn't
just doing it per-process make more sense? Even grouping would be
better done along the traditional process hierarchy, no? And
per-cgroup accounting can be trivially achieved from userland by just
accumulating the stats according to the process's cgroup membership.
What am I missing here?


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