linux-kernel - Re: [PATCH v2] isolcpus: affine kernel threads to specified cpumask

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Date:   Thu, 26 Mar 2020 17:51:29 +0100
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Chris Friesen <chris.friesen@...driver.com>
Cc:     David Laight <David.Laight@...LAB.COM>,
        'Marcelo Tosatti' <mtosatti@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Christoph Lameter <cl@...ux.com>,
        Jim Somerville <Jim.Somerville@...driver.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v2] isolcpus: affine kernel threads to specified cpumask

On Thu, Mar 26, 2020 at 10:32:51AM -0600, Chris Friesen wrote:
> On 3/26/2020 10:22 AM, Frederic Weisbecker wrote:
> > On Wed, Mar 25, 2020 at 06:05:27PM +0000, David Laight wrote:
> 
> > > How about making it possible to change the default affinity
> > > for new kthreads at run time?
> > > Is it possible to change the affinity of existing threads?
> > > Or maybe only those that didn't specify an explicit one??
> > 
> > That's already possible yes, most unbound kthreads are accessible
> > through /proc including kthreadd from which new kthread will inherit
> > their CPU affinity.
> 
> Are you sure that the new kthread will inherit the CPU affinity?
> 
> __kthread_create_on_node() explicitly sets the new thread as SCHED_NORMAL
> with a mask of "cpu_all_mask".

Ah, ok that's the part I missed. What a weird behaviour...

Anyway, I'm working on making all those isolcpus options
controllable through cpusets. So that should be possible at some
future.