linux-kernel - Re: [patch V2 1/9] softirq: Add RT specific softirq accounting

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Message-ID: <20201207130639.GB122233@lothringen>
Date:   Mon, 7 Dec 2020 14:06:39 +0100
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Paul McKenney <paulmck@...nel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: Re: [patch V2 1/9] softirq: Add RT specific softirq accounting

On Fri, Dec 04, 2020 at 06:01:52PM +0100, Thomas Gleixner wrote:
> From: Thomas Gleixner <tglx@...utronix.de>
> 
> RT requires the softirq processing and local bottomhalf disabled regions to
> be preemptible. Using the normal preempt count based serialization is
> therefore not possible because this implicitely disables preemption.
> 
> RT kernels use a per CPU local lock to serialize bottomhalfs. As
> local_bh_disable() can nest the lock can only be acquired on the outermost
> invocation of local_bh_disable() and released when the nest count becomes
> zero. Tasks which hold the local lock can be preempted so its required to
> keep track of the nest count per task.
> 
> Add a RT only counter to task struct and adjust the relevant macros in
> preempt.h.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

Reviewed-by: Frederic Weisbecker <frederic@...nel.org>