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Date: Tue, 17 Jan 2017 13:31:32 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Vikas Shivappa <vikas.shivappa@linux.intel.com>,
        vikas.shivappa@intel.com, davidcc@google.com, eranian@google.com,
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Subject: Re: [PATCH 05/12] x86/cqm,perf/core: Cgroup support prepare
Message-ID: <20170117123132.GB6485@twins.programming.kicks-ass.net>
References: <1483740005-23499-1-git-send-email-vikas.shivappa@linux.intel.com>
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 <alpine.DEB.2.20.1701171135370.3495@nanos>
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On Tue, Jan 17, 2017 at 01:11:50PM +0100, Thomas Gleixner wrote:
> On Fri, 6 Jan 2017, Vikas Shivappa wrote:
> 
> > From: David Carrillo-Cisneros <davidcc@google.com>
> > 
> > cgroup hierarchy monitoring is not supported currently. This patch
> > builds all the necessary datastructures, cgroup APIs like alloc, free
> > etc and necessary quirks for supporting cgroup hierarchy monitoring in
> > later patches.
> > 
> > - Introduce a architecture specific data structure arch_info in
> > perf_cgroup to keep track of RMIDs and cgroup hierarchical monitoring.
> > - perf sched_in calls all the cgroup ancestors when a cgroup is
> > scheduled in. This will not work with cqm as we have a common per pkg
> > rmid associated with one task and hence cannot write different RMIds
> > into the MSR for each event. cqm driver enables a flag
> > PERF_EV_CGROUP_NO_RECURSION which indicates the perf to not call all
> > ancestor cgroups for each event and let the driver handle the hierarchy
> > monitoring for cgroup.
> > - Introduce event_terminate as event_destroy is called after cgrp is
> > disassociated from the event to support rmid handling of the cgroup.
> > This helps cqm clean up the cqm specific arch_info.
> > - Add the cgroup APIs for alloc,free,attach and can_attach
> > 
> > The above framework will be used to build different cgroup features in
> > later patches.
> 
> That's not a framework. It's a hodgepodge of core and x86 specific changes.

Trainwreck comes to mind. It completely fails to describe semantics of
the hacks and how they would preserve the cgroup invariants.