linux-kernel - Re: [PATCH v5 7/9] arm64: Topology, rename cluster

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Date:   Mon, 18 Dec 2017 15:47:03 +0000
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     Morten Rasmussen <morten.rasmussen@...s.arm.com>
Cc:     Jeremy Linton <jeremy.linton@....com>, linux-acpi@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, sudeep.holla@....com,
        hanjun.guo@...aro.org, rjw@...ysocki.net, will.deacon@....com,
        catalin.marinas@....com, gregkh@...uxfoundation.org,
        viresh.kumar@...aro.org, mark.rutland@....com,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        jhugo@...eaurora.org, wangxiongfeng2@...wei.com,
        Jonathan.Zhang@...ium.com, ahs3@...hat.com,
        Jayachandran.Nair@...ium.com, austinwc@...eaurora.org,
        lenb@...nel.org, morten.rasmussen@....com, dietmar.eggemann@....com
Subject: Re: [PATCH v5 7/9] arm64: Topology, rename cluster_id

On Mon, Dec 18, 2017 at 12:42:29PM +0000, Morten Rasmussen wrote:
> On Fri, Dec 15, 2017 at 10:36:35AM -0600, Jeremy Linton wrote:
> > Hi,
> > 
> > On 12/13/2017 12:02 PM, Lorenzo Pieralisi wrote:
> > >[+Morten, Dietmar]
> > >
> > >$SUBJECT should be:
> > >
> > >arm64: topology: rename cluster_id
> > 
> > Sure..
> > 
> > >
> > >On Fri, Dec 01, 2017 at 04:23:28PM -0600, Jeremy Linton wrote:
> > >>Lets match the name of the arm64 topology field
> > >>to the kernel macro that uses it.
> > >>
> > >>Signed-off-by: Jeremy Linton <jeremy.linton@....com>
> > >>---
> > >>  arch/arm64/include/asm/topology.h |  4 ++--
> > >>  arch/arm64/kernel/topology.c      | 27 ++++++++++++++-------------
> > >>  2 files changed, 16 insertions(+), 15 deletions(-)
> > >>
> > >>diff --git a/arch/arm64/include/asm/topology.h b/arch/arm64/include/asm/topology.h
> > >>index c4f2d50491eb..118136268f66 100644
> > >>--- a/arch/arm64/include/asm/topology.h
> > >>+++ b/arch/arm64/include/asm/topology.h
> > >>@@ -7,14 +7,14 @@
> > >>  struct cpu_topology {
> > >>  	int thread_id;
> > >>  	int core_id;
> > >>-	int cluster_id;
> > >>+	int physical_id;
> > >
> > >package_id ?
> > 
> > Given the macro is topology_physical_package_id, either makes sense to me.
> > <shrug> I will change it in the next set.
> 
> I would vote for package_id too. arch/arm has 'socket_id' though.
> 
> > >
> > >It has been debated before, I know. Should we keep the cluster_id too
> > >(even if it would be 1:1 mapped to package_id - for now) ?
> > 
> > Well given that this patch replaces the patch that did that at your
> > request..
> > 
> > I was hoping someone else would comment here, but my take at this point is
> > that it doesn't really matter in a functional sense at the moment.
> > Like the chiplet discussion it can be the subject of a future patch along
> > with the patches which tweak the scheduler to understand the split.
> > 
> > BTW, given that i'm OoO next week, and the following that are the holidays,
> > I don't intend to repost this for a couple weeks. I don't think there are
> > any issues with this set.
> > 
> > >
> > >There is also arch/arm to take into account, again, this patch is
> > >just renaming (as it should have named since the beginning) a
> > >topology level but we should consider everything from a legacy
> > >perspective.
> 
> arch/arm has gone for thread/core/socket for the three topology levels
> it supports.
> 
> I'm not sure what short term value keeping cluster_id has? Isn't it just
> about where we make the package = cluster assignment? Currently it is in
> the definition of topology_physical_package_id. If we keep cluster_id
> and add package_id, it gets moved into the MPIDR/DT parsing code. 
> 
> Keeping cluster_id and introducing a topology_cluster_id function could
> help cleaning up some of the users of topology_physical_package_id that
> currently assumes package_id == cluster_id though.

I think we should settle for a name (eg package_id), remove cluster_id
and convert arch/arm socket_id to the same naming used on arm64 (for
consistency - it is just a variable rename).

This leaves us with the naming "cluster" only in DT topology bindings,
which should be fine, given that "cluster" in that context is just a
"processor-container" - yes we could have chosen a better naming in
the first place but that's what it is.

We should nuke the existing users of topology_physical_package_id()
to identify clusters, I would not add another function for that purpose,
let's nip it in the bud.

Lorenzo