linux-kernel - Re: [RFC 1/3] rcu: Expedite the rcu quiescent state reporting if help needed

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Message-ID: <20190701135346.GA167294@google.com>
Date:   Mon, 1 Jul 2019 09:53:46 -0400
From:   Joel Fernandes <joel@...lfernandes.org>
To:     linux-kernel@...r.kernel.org
Cc:     Josh Triplett <josh@...htriplett.org>, kernel-team@...roid.com,
        Lai Jiangshan <jiangshanlai@...il.com>,
        linux-kselftest@...r.kernel.org,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        "Paul E. McKenney" <paulmck@...ux.ibm.com>, rcu@...r.kernel.org,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Shuah Khan <shuah@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [RFC 1/3] rcu: Expedite the rcu quiescent state reporting if
 help needed

On Mon, Jul 01, 2019 at 12:04:13AM -0400, Joel Fernandes (Google) wrote:
> The t->rcu_read_unlock_special union's need_qs bit can be set by the
> scheduler tick (in rcu_flavor_sched_clock_irq) to indicate that help is
> needed from the rcu_read_unlock path. When this help arrives however, we
> can do better to speed up the quiescent state reporting which if
> rcu_read_unlock_special::need_qs is set might be quite urgent. Make use
> of this information in deciding when to do heavy-weight softirq raising
> where possible.

Just fyi, TREE01-06, SRCU-N and SRCU-t passed overnight testing with this series.