linux-kernel - Re: [PATCH V2] cpuset: Add knob to make allowed masks hotplug invariant on legacy hierarchy

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Date:	Wed, 15 Apr 2015 11:48:02 -0400
From:	Tejun Heo <tj@...nel.org>
To:	"Serge E. Hallyn" <serge@...lyn.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	svaidy@...ux.vnet.ibm.com, nacc@...ux.vnet.ibm.com,
	rjw@...ysocki.net, linux-kernel@...r.kernel.org,
	lizefan@...wei.com, anton@...ba.org, bharata@...ux.vnet.ibm.com,
	cgroups@...r.kernel.org, paulmck@...ux.vnet.ibm.com,
	mingo@...nel.org
Subject: Re: [PATCH V2] cpuset: Add knob to make allowed masks hotplug
 invariant on legacy hierarchy

On Wed, Apr 15, 2015 at 10:30:35AM -0500, Serge E. Hallyn wrote:
> On Wed, Apr 15, 2015 at 05:19:26PM +0200, Peter Zijlstra wrote:
> > On Wed, Apr 15, 2015 at 10:03:02AM -0500, Serge E. Hallyn wrote:
> > 
> > > Peter, is the question "why can't we just use the unified hierarchy for
> > > cpusets"?
> > 
> > No, the question is why can't you use the unified hierarchy cpuset
> > semantics -- without the actual unified hierarchy stuff.
> 
> Ok - that I don't know the answer to.  Does sound like it would
> simplify things, reduce # of sets of semantics.

What'd be the reason for not using the unified hierarchy tho?  The
adaptable required isn't that big and the patchset already proposes
significant amount of behavior change.  Sure it'd be a bit more hassle
but does that really justify introducing yet another operation mode?
This is why unified hierarchy is being added in the first place.  One
can argue "but *I* just need this specific part changed" but allowing
combinations of all those little variations is gonna lead us to a
hellish place.

Thanks.

-- 
tejun
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