linux-kernel - Re: [PATCH v2 04/11] arch_topology: Reset all cpus in reset_cpu

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Date:   Tue, 14 Apr 2020 11:03:24 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Jiaxun Yang <jiaxun.yang@...goat.com>
Cc:     linux-mips@...r.kernel.org, dietmar.eggemann@....com,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Huacai Chen <chenhc@...ote.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Robert Richter <rric@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
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        Zhou Yanjie <zhouyanjie@...o.com>,
        周琰杰 (Zhou Yanjie) 
        <zhouyanjie@...yeetech.com>, YunQiang Su <syq@...ian.org>,
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        Serge Semin <fancer.lancer@...il.com>,
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        afzal mohammed <afzal.mohd.ma@...il.com>,
        Peter Xu <peterx@...hat.com>,
        Kamal Dasu <kdasu.kdev@...il.com>,
        Oleksij Rempel <linux@...pel-privat.de>,
        Sudeep Holla <sudeep.holla@....com>,
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        linux-pm@...r.kernel.org
Subject: Re: [PATCH v2 04/11] arch_topology: Reset all cpus in
 reset_cpu_topology

On Tue, Apr 14, 2020 at 04:35:14PM +0800, Jiaxun Yang wrote:
> On Tue, 14 Apr 2020 09:27:34 +0100
> Sudeep Holla <sudeep.holla@....com> wrote:
>
> > On Sun, Apr 12, 2020 at 11:20:34AM +0800, Jiaxun Yang wrote:
> > > For MIPS platform, when topology isn't probed by DeviceTree,
> > > possible_cpu might be empty when calling init_cpu_topology,
> > > that may result cpu_topology not fully reseted for all CPUs.
> > > So here we can reset all cpus instead of possible cpus.
> > >
> >
> > As I have told before adjust and make it default before this function
> > gets called.
>
> Hi,
>
> That's really impossible under current MIPS code structure.
>

I really doubt that, but I have no knowledge on MIPS port, so I would
let maintainers take that call.

> Another option would be prefill possible_cpu with all_cpu_mask before
> calling topology_init, but that would make the code unnecessarily
> complex.
>

I still prefer that. By the time we call this function on a config
with say NR_CPUS=1024, we would have parsed DT and set nr_cpus to say 8
or 16 just for sake of example, so if platforms can't figure the
possible CPUs, let them set it to NR_CPUs so that not all platforms
have to run through that loop.

> Here simply reset the whole array won't cause any regression.
>

Not necessary, please discuss and check if some simplification to MIPS
can be done rather than patching here and there to make it work.

--
Regards,
Sudeep