linux-kernel - Re: [PATCH] workqueue: add cmdline parameter `unbound_workqueue_cpus` to further constrain wq_unbound

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Date:   Wed, 21 Jun 2023 20:47:54 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     tj@...nel.org, jiangshanlai@...il.com,
        linux-kernel@...r.kernel.org, zyhtheonly@...h.net,
        zwp10758@...il.com, zyhtheonly@...il.com
Subject: Re: [PATCH] workqueue: add cmdline parameter `unbound_workqueue_cpus`
 to further constrain wq_unbound_cpumask at boot time



On 6/21/23 20:34, tiozhang wrote:
> Motivation of doing this is to better improve boot times for devices when
> we want to prevent our workqueue works from running on some specific CPUs,
> e,g, some CPUs are busy with interrupts.
> 
> Signed-off-by: tiozhang <tiozhang@...iglobal.com>
> ---
>  kernel/workqueue.c | 25 +++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)
> 

Documentation for this new command line parameter should be added to
Documentation/admin-guide/kernel-parameters.rst (in alphabetical order).

Thanks.

> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index 7cd5f5e7e0a1..47e7b29df5fe 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -329,6 +329,9 @@ static bool workqueue_freezing;		/* PL: have wqs started freezing? */
>  /* PL: allowable cpus for unbound wqs and work items */
>  static cpumask_var_t wq_unbound_cpumask;
>  
> +/* for further constrain wq_unbound_cpumask by cmdline parameter*/
> +static cpumask_var_t wq_cmdline_cpumask;
> +
>  /* CPU where unbound work was last round robin scheduled from this CPU */
>  static DEFINE_PER_CPU(int, wq_rr_cpu_last);
>  
> @@ -6006,6 +6009,10 @@ void __init workqueue_init_early(void)
>  	cpumask_copy(wq_unbound_cpumask, housekeeping_cpumask(HK_TYPE_WQ));
>  	cpumask_and(wq_unbound_cpumask, wq_unbound_cpumask, housekeeping_cpumask(HK_TYPE_DOMAIN));
>  
> +	if (!cpumask_empty(wq_cmdline_cpumask))
> +		cpumask_and(wq_unbound_cpumask, wq_unbound_cpumask, wq_cmdline_cpumask);
> +	free_bootmem_cpumask_var(wq_cmdline_cpumask);
> +
>  	pwq_cache = KMEM_CACHE(pool_workqueue, SLAB_PANIC);
>  
>  	/* initialize CPU pools */
> @@ -6129,3 +6136,21 @@ void __init workqueue_init(void)
>   */
>  void __warn_flushing_systemwide_wq(void) { }
>  EXPORT_SYMBOL(__warn_flushing_systemwide_wq);
> +
> +
> +static int __init unbound_workqueue_cpus_setup(char *str)
> +{
> +	cpumask_var_t cpumask;
> +
> +	alloc_bootmem_cpumask_var(&wq_cmdline_cpumask);
> +	alloc_bootmem_cpumask_var(&cpumask);
> +	if (cpulist_parse(str, cpumask) < 0)
> +		pr_warn("unbound_workqueue_cpus: incorrect CPU range\n");
> +	else
> +		cpumask_copy(wq_cmdline_cpumask, cpumask);
> +
> +	free_bootmem_cpumask_var(cpumask);
> +
> +	return 0;
> +}
> +__setup("unbound_workqueue_cpus=", unbound_workqueue_cpus_setup);

-- 
~Randy