linux-kernel - Re: [patch 3/4] isolcpus: affine kernel threads to housekeeping cpus

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Date:   Wed, 1 Apr 2020 15:32:43 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Marcelo Tosatti <mtosatti@...hat.com>, linux-kernel@...r.kernel.org
Cc:     Frederic Weisbecker <fweisbec@...il.com>,
        Chris Friesen <chris.friesen@...driver.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jim Somerville <Jim.Somerville@...driver.com>,
        Christoph Lameter <cl@...ux.com>
Subject: Re: [patch 3/4] isolcpus: affine kernel threads to housekeeping cpus

On 4/1/20 5:10 AM, Marcelo Tosatti wrote:
> This is a kernel enhancement that configures the cpu affinity of kernel
> threads via kernel boot option nohz_full=.
> 
> 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 (see kernel-parameters.txt).
> 
> Note-1: this is based off on Wind River's patch at
> https://github.com/starlingx-staging/stx-integ/blob/master/kernel/kernel-std/centos/patches/affine-compute-kernel-threads.patch
> 
> Difference being that this patch is limited to modifying
> kernel thread cpumask: Behaviour of other threads can
> be controlled via cgroups or sched_setaffinity.
> 
> Note-2: Wind River's patch was based off Christoph Lameter's patch at
> https://lwn.net/Articles/565932/ with the only difference being
> the kernel parameter changed from kthread to kthread_cpus.
> 
> Signed-off-by: Marcelo Tosatti <mtosatti@...hat.com>
> 

Hi Marcelo,

> ---
>  Documentation/admin-guide/kernel-parameters.txt |    8 ++++++++

Patch is missing those Docum bits.

>  include/linux/sched/isolation.h                 |    1 +
>  kernel/kthread.c                                |    6 ++++--
>  kernel/sched/isolation.c                        |    6 ++++++
>  4 files changed, 19 insertions(+), 2 deletions(-)
> 
> Index: linux-2.6/include/linux/sched/isolation.h
> ===================================================================
> --- linux-2.6.orig/include/linux/sched/isolation.h
> +++ linux-2.6/include/linux/sched/isolation.h
> @@ -14,6 +14,7 @@ enum hk_flags {
>  	HK_FLAG_DOMAIN		= (1 << 5),
>  	HK_FLAG_WQ		= (1 << 6),
>  	HK_FLAG_MANAGED_IRQ	= (1 << 7),
> +	HK_FLAG_KTHREAD		= (1 << 8),
>  };
>  
>  #ifdef CONFIG_CPU_ISOLATION
> Index: linux-2.6/kernel/kthread.c
> ===================================================================
> --- linux-2.6.orig/kernel/kthread.c
> +++ linux-2.6/kernel/kthread.c
> @@ -23,6 +23,7 @@
>  #include <linux/ptrace.h>
>  #include <linux/uaccess.h>
>  #include <linux/numa.h>
> +#include <linux/sched/isolation.h>
>  #include <trace/events/sched.h>
>  
>  static DEFINE_SPINLOCK(kthread_create_lock);
> @@ -347,7 +348,8 @@ struct task_struct *__kthread_create_on_
>  		 * The kernel thread should not inherit these properties.
>  		 */
>  		sched_setscheduler_nocheck(task, SCHED_NORMAL, &param);
> -		set_cpus_allowed_ptr(task, cpu_possible_mask);
> +		set_cpus_allowed_ptr(task,
> +				     housekeeping_cpumask(HK_FLAG_KTHREAD));
>  	}
>  	kfree(create);
>  	return task;
> @@ -572,7 +574,7 @@ int kthreadd(void *unused)
>  	/* Setup a clean context for our children to inherit. */
>  	set_task_comm(tsk, "kthreadd");
>  	ignore_signals(tsk);
> -	set_cpus_allowed_ptr(tsk, cpu_possible_mask);
> +	set_cpus_allowed_ptr(tsk, housekeeping_cpumask(HK_FLAG_KTHREAD));
>  	set_mems_allowed(node_states[N_MEMORY]);
>  
>  	current->flags |= PF_NOFREEZE;
> Index: linux-2.6/kernel/sched/isolation.c
> ===================================================================
> --- linux-2.6.orig/kernel/sched/isolation.c
> +++ linux-2.6/kernel/sched/isolation.c
> @@ -141,7 +141,7 @@ static int __init housekeeping_nohz_full
>  	unsigned int flags;
>  
>  	flags = HK_FLAG_TICK | HK_FLAG_WQ | HK_FLAG_TIMER | HK_FLAG_RCU |
> -		HK_FLAG_MISC | HK_FLAG_SCHED;
> +		HK_FLAG_MISC | HK_FLAG_SCHED | HK_FLAG_KTHREAD;
>  
>  	return housekeeping_setup(str, flags);
>  }
> 
> 

thanks.
-- 
~Randy