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

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Date:   Thu, 19 Jan 2017 11:59:21 -0800 (PST)
From:   Shivappa Vikas <vikas.shivappa@...el.com>
To:     Peter Zijlstra <peterz@...radead.org>
cc:     Thomas Gleixner <tglx@...utronix.de>,
        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


Hello Peterz,

On Wed, 18 Jan 2017, Peter Zijlstra wrote:

> 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 1/12 Documentation patch describes the interface. Basically we are just 
trying to support the task and cgroup monitoring.

By the design document, do you want a document describing how we enable the 
cgroup for cqm since its a special case?
(which would include all the arch_info in the perf_cgroup we add to keep track 
of hierarchy in the driver , etc ..)

Thanks,
Vikas

>
> 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.
>