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Subject: Re: [PATCH] affine kernel threads to specified cpumask
To:     Thomas Gleixner <tglx@linutronix.de>,
        Marcelo Tosatti <mtosatti@redhat.com>,
        linux-kernel@vger.kernel.org
Cc:     Christoph Lameter <cl@linux.com>, Vu Tran <vu.tran@windriver.com>,
        Jim Somerville <Jim.Somerville@windriver.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Peter Zijlstra <peterz@infradead.org>
References: <20200323135414.GA28634@fuller.cnet>
 <87k13boxcn.fsf@nanos.tec.linutronix.de>
From:   Chris Friesen <chris.friesen@windriver.com>
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Date:   Mon, 23 Mar 2020 11:02:37 -0600
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On 3/23/2020 10:22 AM, Thomas Gleixner wrote:
> Marcelo,
> Marcelo Tosatti <mtosatti@redhat.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