linux-kernel - Re: [PATCH 3/4] workqueue: add schedule_on_each

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Date:   Mon, 5 Jun 2023 09:12:19 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Marcelo Tosatti <mtosatti@...hat.com>
Cc:     Christoph Lameter <cl@...ux.com>,
        Aaron Tomlin <atomlin@...mlin.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Vlastimil Babka <vbabka@...e.cz>, Tejun Heo <tj@...nel.org>,
        Lai Jiangshan <jiangshanlai@...il.com>
Subject: Re: [PATCH 3/4] workqueue: add schedule_on_each_cpumask helper

On Fri 02-06-23 14:04:28, Marcelo Tosatti wrote:
> On Fri, Jun 02, 2023 at 12:48:23PM +0200, Michal Hocko wrote:
[...]
> > > +	if (!alloc_cpumask_var(&effmask, GFP_KERNEL)) {
> > > +		free_percpu(works);
> > > +		return -ENOMEM;
> > > +	}
> > > +
> > > +	cpumask_and(effmask, cpumask, cpu_online_mask);
> > > +
> > > +	cpus_read_lock();
> > > +
> > > +	for_each_cpu(cpu, effmask) {
> > 
> > Is the cpu_online_mask dance really necessary? 
> 
> > Why cannot you simply do for_each_online_cpu here? 
> 
> Are you suggesting to do: 
> 
> 	for_each_online_cpu(cpu) {
> 		if cpu is not in cpumask
> 			continue;
> 		...
> 	}
> 
> This does not seem efficient.

Are you sure this is less sufficient than a memory allocation?
-- 
Michal Hocko
SUSE Labs