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

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Message-ID: <20200326112832.GC17019@fuller.cnet>
Date:   Thu, 26 Mar 2020 08:28:32 -0300
From:   Marcelo Tosatti <mtosatti@...hat.com>
To:     David Laight <David.Laight@...lab.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Chris Friesen <chris.friesen@...driver.com>,
        "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 Wed, Mar 25, 2020 at 06:05:27PM +0000, David Laight wrote:
> From: Marcelo Tosatti
> > Sent: 24 March 2020 15:20
> > 
> > This is a kernel enhancement to configure the cpu affinity of kernel
> > threads via kernel boot option isolcpus=no_kthreads,<isolcpus_params>,<cpulist>
> > 
> > When this option is specified, the cpumask is immediately applied upon
> > thread launch. This does not affect kernel threads that specify cpu
> > and node.
> > 
> > This allows CPU isolation (that is not allowing certain threads
> > to execute on certain CPUs) without using the isolcpus=domain parameter,
> > making it possible to enable load balancing on such CPUs
> > during runtime
> ...
> 
> 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??
> 
> 	David
> 
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)

Hi David,

Problem with that approach is the window between kernel thread creation 
and cpumask change.