linux-kernel - Re: [PATCH v1 1/1] wq: Avoid using isolated cpus' timers on unbounded queue_delayed

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Date: Mon, 29 Jan 2024 08:18:15 -1000
From: Tejun Heo <tj@...nel.org>
To: Leonardo Bras <leobras@...hat.com>
Cc: Lai Jiangshan <jiangshanlai@...il.com>,
	Marcelo Tosatti <mtosatti@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 1/1] wq: Avoid using isolated cpus' timers on
 unbounded queue_delayed_work

Hello,

On Fri, Jan 26, 2024 at 07:05:35PM -0300, Leonardo Bras wrote:
> > 	if (housekeeping_enabled(HK_TYPE_TIMER)) {
> > 		cpu = smp_processor_id();
> > 		if (!housekeeping_test_cpu(cpu, HK_TYPE_TIMER))
> > 			cpu = housekeeping_any_cpu(HK_TYPE_TIMER);
> > 		add_timer_on(timer, cpu);
> > 	} else {
> > 		if (likely(cpu == WORK_CPU_UNBOUND))
> > 			add_timer(timer, cpu);
> > 		else
> > 			add_timer_on(timer, cpu);
> > 	}
> > 
> > Thanks.
> 
> I am not really against it, but for me it's kind of weird to have that many 
> calls to add_timer_on() if we can avoid it. 
> 
> I would rather go with:
> 
> ###
> if (unlikely(cpu != WORK_CPU_UNBOUND)) {
> 	add_timer_on(timer, cpu);
> 	return;
> }
> 
> if (!housekeeping_enabled(HK_TYPE_TIMER)) {
> 	add_timer(timer);
> 	return;
> }
> 
> cpu = smp_processor_id();
> if (!housekeeping_test_cpu(cpu, HK_TYPE_TIMER))
> 	cpu = housekeeping_any_cpu(HK_TYPE_TIMER);
> 
> add_timer_on(timer, cpu);
> ###
> 
> What do you think?

Isn't that still the same number of add_timer[_on]() calls?

Thanks.

-- 
tejun