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

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Date:   Mon, 23 Mar 2020 11:02:37 -0600
From:   Chris Friesen <chris.friesen@...driver.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        linux-kernel@...r.kernel.org
Cc:     Christoph Lameter <cl@...ux.com>, Vu Tran <vu.tran@...driver.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] affine kernel threads to specified cpumask

On 3/23/2020 10:22 AM, Thomas Gleixner wrote:
> Marcelo,
> Marcelo Tosatti <mtosatti@...hat.com> writes:
> 
> the subject lacks a prefix and the CC list a few people.
> 
>> This is a kernel enhancement to configure the cpu affinity of kernel
>> threads via kernel boot option kthread_cpus=<cpulist>.
>>
>> With kthread_cpus 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= parameter,
>> making it possible to enable load balancing on such CPUs
>> during runtime.
> 
> I'm surely missing some background information, but that sentence does
> not make any sense to me.
> 
> Thanks,
> 
>          tglx
> 

The idea is to affine general kernel threads to specific "housekeeping" 
CPUs, while still allowing load balancing of tasks.

The isolcpus= boot parameter would prevent kernel threads from running 
on the isolated CPUs, but it disables load balancing on the isolated CPUs.

Chris