linux-kernel - Re: [RFC PATCH v2 4/5] softirq: Unify should_wakeup

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Message-ID: <20240904121513.GH4723@noisy.programming.kicks-ass.net>
Date: Wed, 4 Sep 2024 14:15:13 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: K Prateek Nayak <kprateek.nayak@....com>
Cc: Ingo Molnar <mingo@...hat.com>, Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Leonardo Bras <leobras@...hat.com>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Rik van Riel <riel@...riel.com>,
	Thorsten Blum <thorsten.blum@...lux.com>,
	Zqiang <qiang.zhang1211@...il.com>, Tejun Heo <tj@...nel.org>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Caleb Sander Mateos <csander@...estorage.com>,
	linux-kernel@...r.kernel.org,
	"Gautham R . Shenoy" <gautham.shenoy@....com>,
	Chen Yu <yu.c.chen@...el.com>, Julia Lawall <Julia.Lawall@...ia.fr>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: Re: [RFC PATCH v2 4/5] softirq: Unify should_wakeup_ksoftirqd()

On Wed, Sep 04, 2024 at 11:12:22AM +0000, K Prateek Nayak wrote:

> @@ -118,14 +101,40 @@ EXPORT_PER_CPU_SYMBOL_GPL(hardirq_context);
>   * the task which is in a softirq disabled section is preempted or blocks.
>   */
>  struct softirq_ctrl {
> +#ifdef CONFIG_PREEMPT_RT
>  	local_lock_t	lock;
> +#endif
>  	int		cnt;
>  };
>  
> -static DEFINE_PER_CPU(struct softirq_ctrl, softirq_ctrl) = {
> +static DEFINE_PER_CPU_ALIGNED(struct softirq_ctrl, softirq_ctrl) = {
> +#ifdef CONFIG_PREEMPT_RT
>  	.lock	= INIT_LOCAL_LOCK(softirq_ctrl.lock),
> +#endif
>  };

With the exception of CONFIG_DEBUG_LOCK_ALLOC (part of LOCKDEP)
local_lock_t is an empty structure when PREEMPT_RT=n.

That is to say, you can probably get by without those extra #ifdefs.