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

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Message-ID: <20180103142934.GA5390@e107155-lin>
Date:   Wed, 3 Jan 2018 14:29:34 +0000
From:   Sudeep Holla <sudeep.holla@....com>
To:     Xiongfeng Wang <wangxiongfeng2@...wei.com>,
        Morten Rasmussen <morten.rasmussen@...s.arm.com>,
        Jeremy Linton <jeremy.linton@....com>
Cc:     Sudeep Holla <sudeep.holla@....com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        linux-acpi@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        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, 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 02/01/18 02:29, Xiongfeng Wang wrote:
> Hi,
> 
> On 2017/12/18 20:42, 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
>>>
> [cut]
>>>
> I think we still need the information describing which cores are in one
> cluster. Many arm64 chips have the architecture core/cluster/socket. Cores
> in one cluster may share a same L2 cache. That information can be used to
> build the sched_domain. If we put cores in one cluster in one sched_domain,
> the performance will be better.(please see kernel/sched/topology.c:1197,
> cpu_coregroup_mask() uses 'core_sibling' to build a multi-core
> sched_domain).

We get all the cache information from DT/ACPI PPTT(mainly topology) and now
even the geometry. So ideally, the sharing information must come from that.
Any other solution might end up in conflict if DT/PPTT and that mismatch.

> So I think we still need variable to record which cores are in one
> sched_domain for future use.

I tend to say no, at-least not as is.
-- 
Regards,
Sudeep