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

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Date:   Wed, 18 Jan 2017 10:56:58 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Shivappa Vikas <vikas.shivappa@...el.com>,
        Vikas Shivappa <vikas.shivappa@...ux.intel.com>,
        davidcc@...gle.com, eranian@...gle.com,
        linux-kernel@...r.kernel.org, x86@...nel.org, hpa@...or.com,
        mingo@...nel.org, ravi.v.shankar@...el.com, tony.luck@...el.com,
        fenghua.yu@...el.com, andi.kleen@...el.com, h.peter.anvin@...el.com
Subject: Re: [PATCH 00/12] Cqm2: Intel Cache quality monitoring fixes

On Wed, Jan 18, 2017 at 09:53:02AM +0100, Thomas Gleixner wrote:
> The whole approach you and David have taken is to whack some desired cgroup
> functionality and whatever into CQM without rethinking the overall
> design. And that's fundamentaly broken because it does not take cache (and
> memory bandwidth) allocation into account.
> 
> I seriously doubt, that the existing CQM/MBM code can be refactored in any
> useful way. As Peter Zijlstra said before: Remove the existing cruft
> completely and start with completely new design from scratch.
> 
> And this new design should start from the allocation angle and then add the
> whole other muck on top so far its possible. Allocation related monitoring
> must be the primary focus, everything else is just tinkering.

Agreed, the little I have seen of these patches is quite horrible. And
there seems to be a definite lack of design; or at the very least an
utter lack of communication of it.

The approach, in so far that I could make sense of it, seems to utterly
rape perf-cgroup. I think Thomas makes a sensible point in trying to
match it to the CAT stuffs.