Date:	Fri, 28 Jun 2013 11:44:23 -0700
From:	Tim Hockin <thockin@...kin.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	Li Zefan <lizefan@...wei.com>,
	Containers <containers@...ts.linux-foundation.org>,
	Cgroups <cgroups@...r.kernel.org>,
	bsingharora <bsingharora@...il.com>,
	"dhaval.giani" <dhaval.giani@...il.com>,
	Kay Sievers <kay.sievers@...y.org>,
	jpoimboe <jpoimboe@...hat.com>,
	"Daniel P. Berrange" <berrange@...hat.com>,
	lpoetter <lpoetter@...hat.com>,
	workman-devel <workman-devel@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	dawnchen@...gle.com, Paul Turner <pjt@...gle.com>
Subject: Re: cgroup: status-quo and userland efforts

On Thu, Jun 27, 2013 at 2:04 PM, Tejun Heo <tj@...nel.org> wrote:
> Hello,
>
> On Thu, Jun 27, 2013 at 01:46:18PM -0700, Tim Hockin wrote:
>> So what you're saying is that you don't care that this new thing is
>> less capable than the old thing, despite it having real impact.
>
> Sort of.  I'm saying, at least up until now, moving away from
> orthogonal hierarchy support seems to be the right trade-off.  It all
> depends on how you measure how much things are simplified and how
> heavy the "real impacts" are.  It's not like these things can be
> determined white and black.  Given the current situation, I think it's
> the right call.

I totally understand where you're coming from - trying to get back to
a stable feature set.  But it sucks to be on the losing end of that
battle - you're cutting things that REALLY matter to us, and without a
really viable alternative.  So we'll keep fighting.

>> If controller C is enabled at level X but disabled at level X/Y, does
>> that mean that X/Y uses the limits set in X?  How about X/Y/Z?
>
> Y and Y/Z wouldn't make any difference.  Tasks belonging to them would
> behave as if they belong to X as far as C is concerened.

OK, that *sounds* sane.  It doesn't solve all our problems, but it
alleviates some of them.

>> So take away some of the flexibility that has minimal impact and
>> maximum return.  Splitting threads across cgroups - we use it, but we
>> could get off that.  Force all-or-nothing joining of an aggregate
>
> Please do so.

Splitting threads is sort of important for some cgroups, like CPU.  I
wonder if pjt is paying attention to this thread.

>> construct (a container vs N cgroups).
>>
>> But perform surgery with a scalpel, not a hatchet.
>
> As anything else, it's drawing a line in a continuous spectrum of
> grey.  Right now, given that maintaining multiple orthogonal
> hierarchies while introducing a proper concept of resource container
> involves addition of completely new constructs and complexity, I don't
> think that's a good option.  If there are problems which can't be
> resolved / worked around in a reasonable manner, please bring them up
> along with their contexts.  Let's examine them and see whether there
> are other ways to accomodate them.

You're arguing that the abstraction you want is that of a "container"
but that it's easier to remove options than to actually build a better
API.

I think this is wrong.  Take the opportunity to define the RIGHT
interface that you WANT - a container.  Implement it in terms of
cgroups (and maybe other stuff!).  Make that API so compelling that
people want to use it, and your war of attrition on direct cgroup
madness will be won, but with net progress rather than regress.
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