linux-kernel - Re: [RFC v2] rcu/tree: Try to invoke_rcu_core() if in

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Date:   Mon, 19 Aug 2019 19:14:38 -0500
From:   Scott Wood <swood@...hat.com>
To:     "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        linux-kernel@...r.kernel.org
Cc:     Josh Triplett <josh@...htriplett.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        "Paul E. McKenney" <paulmck@...ux.ibm.com>, rcu@...r.kernel.org,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [RFC v2] rcu/tree: Try to invoke_rcu_core() if in_irq() during
 unlock

On Sun, 2019-08-18 at 17:49 -0400, Joel Fernandes (Google) wrote:
> When we're in hard interrupt context in rcu_read_unlock_special(), we
> can still benefit from invoke_rcu_core() doing wake ups of rcuc
> threads when the !use_softirq parameter is passed.  This is safe
> to do so because:

What is the benefit, beyond skipping the irq work overhead?  Is there some
reason to specifically want the rcuc thread woken rather than just getting
into the scheduler (and thus rcu_note_context_switch) as soon as possible?

-Scott