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Re: [PATCH tip/core/rcu 3/6] rcu: Abstract dynticks extended quiescent state enter/exit operations

From Peter Zijlstra <peterz@infradead.org>
Newsgroups linux.kernel
Subject Re: [PATCH tip/core/rcu 3/6] rcu: Abstract dynticks extended quiescent state enter/exit operations
Date 2017-01-16 17:50 +0100
Message-ID <t0iDL-30L-1@gated-at.bofh.it> (permalink)
References <sZslP-3NR-3@gated-at.bofh.it> <sZslP-3NR-15@gated-at.bofh.it>
Organization linux.* mail to news gateway

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On Sat, Jan 14, 2017 at 12:54:42AM -0800, Paul E. McKenney wrote:
>  /*
> + * Record entry into an extended quiescent state.  This is only to be
> + * called when not already in an extended quiescent state.
> + */
> +static void rcu_dynticks_eqs_enter(void)
> +{
> +	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
> +
> +	/*
> +	 * CPUs seeing atomic_inc() must see prior RCU read-side critical
> +	 * sections, and we also must force ordering with the next idle
> +	 * sojourn.
> +	 */
> +	smp_mb__before_atomic(); /* See above. */
> +	atomic_inc(&rdtp->dynticks);
> +	smp_mb__after_atomic(); /* See above. */
> +	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
> +		     atomic_read(&rdtp->dynticks) & 0x1);
> +}

In an earlier patch you replaced things with atomic_add_return(), why
not use atomic_inc_return() here?

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Thread

[PATCH tip/core/rcu 0/6] Dynticks updates for 4.11 "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-14 10:00 +0100
  [PATCH tip/core/rcu 3/6] rcu: Abstract dynticks extended quiescent state enter/exit operations "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-14 10:00 +0100
    Re: [PATCH tip/core/rcu 3/6] rcu: Abstract dynticks extended  quiescent state enter/exit operations Josh Triplett <josh@joshtriplett.org> - 2017-01-16 08:50 +0100
      Re: [PATCH tip/core/rcu 3/6] rcu: Abstract dynticks extended  quiescent state enter/exit operations "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-16 12:40 +0100
        Re: [PATCH tip/core/rcu 3/6] rcu: Abstract dynticks extended  quiescent state enter/exit operations Josh Triplett <josh@joshtriplett.org> - 2017-01-16 20:30 +0100
          Re: [PATCH tip/core/rcu 3/6] rcu: Abstract dynticks extended  quiescent state enter/exit operations "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-17 01:20 +0100
    Re: [PATCH tip/core/rcu 3/6] rcu: Abstract dynticks extended  quiescent state enter/exit operations Peter Zijlstra <peterz@infradead.org> - 2017-01-16 17:50 +0100
      Re: [PATCH tip/core/rcu 3/6] rcu: Abstract dynticks extended  quiescent state enter/exit operations "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-16 22:10 +0100
        Re: [PATCH tip/core/rcu 3/6] rcu: Abstract dynticks extended  quiescent state enter/exit operations "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-17 01:10 +0100
  [PATCH tip/core/rcu 4/6] rcu: Abstract extended quiescent state determination "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-14 10:00 +0100
  [PATCH tip/core/rcu 1/6] rcu: Abstract the dynticks momentary-idle operation "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-14 10:00 +0100
    Re: [PATCH tip/core/rcu 1/6] rcu: Abstract the dynticks  momentary-idle operation Josh Triplett <josh@joshtriplett.org> - 2017-01-16 08:50 +0100
      Re: [PATCH tip/core/rcu 1/6] rcu: Abstract the dynticks  momentary-idle operation "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-16 12:30 +0100
        Re: [PATCH tip/core/rcu 1/6] rcu: Abstract the dynticks  momentary-idle operation Josh Triplett <josh@joshtriplett.org> - 2017-01-16 20:00 +0100
          Re: [PATCH tip/core/rcu 1/6] rcu: Abstract the dynticks  momentary-idle operation "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-17 00:50 +0100
  Re: [PATCH tip/core/rcu 0/6] Dynticks updates for 4.11 Josh Triplett <josh@joshtriplett.org> - 2017-01-16 09:00 +0100
  Re: [PATCH tip/core/rcu 0/6] Dynticks updates for 4.11 "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-18 03:50 +0100
    [PATCH v2 tip/core/rcu 3/6] rcu: Abstract dynticks extended quiescent state enter/exit operations "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-18 03:50 +0100
      Re: [PATCH v2 tip/core/rcu 3/6] rcu: Abstract dynticks extended  quiescent state enter/exit operations Josh Triplett <josh@joshtriplett.org> - 2017-01-21 21:50 +0100
        Re: [PATCH v2 tip/core/rcu 3/6] rcu: Abstract dynticks extended  quiescent state enter/exit operations "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-23 20:50 +0100
    Re: [PATCH v3 tip/core/rcu 0/6] Dynticks updates for 4.11 "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-24 22:50 +0100
      [PATCH v3 tip/core/rcu 4/6] rcu: Abstract extended quiescent state determination "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-24 22:50 +0100
      [PATCH v3 tip/core/rcu 1/6] rcu: Abstract the dynticks momentary-idle operation "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-24 22:50 +0100

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