linux-kernel - Re: [RFC 1/2] rcu: Do prepare and cleanup idle depending on in

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Message-ID: <20180620121156.4da98db2@gandalf.local.home>
Date:   Wed, 20 Jun 2018 12:11:56 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:     Byungchul Park <byungchul.park@....com>, jiangshanlai@...il.com,
        josh@...htriplett.org, mathieu.desnoyers@...icios.com,
        linux-kernel@...r.kernel.org, kernel-team@....com,
        joel@...lfernandes.org
Subject: Re: [RFC 1/2] rcu: Do prepare and cleanup idle depending on
 in_nmi()

On Wed, 20 Jun 2018 08:56:58 -0700
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote:

> OK, so in theory this change is safe from a tracing perspective.  But
> it does add conditionals to a fastpath.

Does it?

I see it replacing two conditions from both rcu_irq_enter/exit() with a
single one in rcu_nmi_enter/exit(). Sure it adds one to rcu_nmi_enter()
but that's a far less fast path than rcu_irq_enter(), which this patch
removes a conditional from.

-- Steve