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

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Message-ID: <20140104161050.GA24306@htj.dyndns.org>
Date:	Sat, 4 Jan 2014 11:10:50 -0500
From:	Tejun Heo <tj@...nel.org>
To:	Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@...el.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Li Zefan <lizefan@...wei.com>,
	containers@...ts.linux-foundation.org, cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/4] x86: Add Cache QoS Monitoring (CQM) support

Hello,

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?

Thanks.

-- 
tejun
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