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

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Message-ID: <20201023074542.GN2611@hirez.programming.kicks-ass.net>
Date:   Fri, 23 Oct 2020 09:45:42 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Elliot Berman <eberman@...eaurora.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        "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
Subject: Re: [PATCH] smp: Add bootcpus parameter to boot subset of CPUs

On Thu, Oct 22, 2020 at 03:04:03PM -0700, 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
> 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.

Why would one wish to do so? Having the ability for abilities sake is no
good.