linux-kernel - Re: [PATCH] smp: Add bootcpus parameter to boot subset of CPUs

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Message-ID: <20201025130642.yurgta7s63aecgrj@e107158-lin>
Date:   Sun, 25 Oct 2020 13:06:42 +0000
From:   Qais Yousef <qais.yousef@....com>
To:     Elliot Berman <eberman@...eaurora.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Trilok Soni <tsoni@...eaurora.org>,
        Prasad Sodagudi <psodagud@...eaurora.org>,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Lukasz Luba <lukasz.luba@....com>,
        Valentin Schneider <valentin.schneider@....com>
Subject: Re: [PATCH] smp: Add bootcpus parameter to boot subset of CPUs

Hi Elliot

On 10/22/20 15:04, Elliot Berman wrote:
> In a heterogeneous multiprocessor system, specifying the 'maxcpus'
> parameter on kernel command line does not provide sufficient control
> over which CPUs are brought online at kernel boot time, since CPUs may
> have nonuniform performance characteristics. Thus, add bootcpus kernel

Are you seeing boot time issues on big.LITTLE systems that's why you need this
extra config? If so it'll be good to elaborate on the problem. Scheduler should
place the heavy tasks on bigs. It'll be good to understand what's failing in
here as this might not be addressing the root cause.

Thanks

--
Qais Yousef

> parameter to control which CPUs should be brought online during kernel
> boot. When both maxcpus and bootcpus is set, the more restrictive of the
> two are booted.