From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Pranith Kumar <bobby.prani@gmail.com>
Cc: Josh Triplett <josh@joshtriplett.org>,
Steven Rostedt <rostedt@goodmis.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Lai Jiangshan <laijs@cn.fujitsu.com>,
"open list:READ-COPY UPDATE..." <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 07/16] rcu: Save and restore irq flags in rcu_gp_cleanup()
Date: Wed, 23 Jul 2014 05:16:15 -0700 [thread overview]
Message-ID: <20140723121615.GI11241@linux.vnet.ibm.com> (raw)
In-Reply-To: <1406092194-13004-8-git-send-email-bobby.prani@gmail.com>
On Wed, Jul 23, 2014 at 01:09:44AM -0400, Pranith Kumar wrote:
> We use raw_spin_lock_irqsave/restore() family of functions throughout the code
> but for two locations. This commit replaces raw_spin_lock_irq()/unlock_irq()
> with irqsave/restore() in one such location. This is not strictly necessary,
> so I did not change the other location. I will update the other location if
> this is accepted :)
>
> This commit changes raw_spin_lock_irq()/unlock_irq() to lock_irqsave()/restore().
>
> Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
I sympathize, as I used to take the approach that you are advocating.
The reason that I changed is that we -know- that interrupts are enabled
at this point in the code, so there is no point in incurring the extra
cognitive and machine overhead of the _irqsave() variant. Plus the
current code has documentation benefits -- it tells you that the author
felt that irqs could not possible be disabled here.
So sorry, but no.
Thanx, Paul
> ---
> kernel/rcu/tree.c | 14 +++++++-------
> 1 file changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index b14cecd..5dcbf36 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -1706,13 +1706,13 @@ static int rcu_gp_fqs(struct rcu_state *rsp, int fqs_state_in)
> */
> static void rcu_gp_cleanup(struct rcu_state *rsp)
> {
> - unsigned long gp_duration;
> + unsigned long gp_duration, flags;
> bool needgp = false;
> int nocb = 0;
> struct rcu_data *rdp;
> struct rcu_node *rnp = rcu_get_root(rsp);
>
> - raw_spin_lock_irq(&rnp->lock);
> + raw_spin_lock_irqsave(&rnp->lock, flags);
> smp_mb__after_unlock_lock();
> gp_duration = jiffies - rsp->gp_start;
> if (gp_duration > rsp->gp_max)
> @@ -1726,7 +1726,7 @@ static void rcu_gp_cleanup(struct rcu_state *rsp)
> * safe for us to drop the lock in order to mark the grace
> * period as completed in all of the rcu_node structures.
> */
> - raw_spin_unlock_irq(&rnp->lock);
> + raw_spin_unlock_irqrestore(&rnp->lock, flags);
>
> /*
> * Propagate new ->completed value to rcu_node structures so
> @@ -1738,7 +1738,7 @@ static void rcu_gp_cleanup(struct rcu_state *rsp)
> * grace period is recorded in any of the rcu_node structures.
> */
> rcu_for_each_node_breadth_first(rsp, rnp) {
> - raw_spin_lock_irq(&rnp->lock);
> + raw_spin_lock_irqsave(&rnp->lock, flags);
> smp_mb__after_unlock_lock();
> ACCESS_ONCE(rnp->completed) = rsp->gpnum;
> rdp = this_cpu_ptr(rsp->rda);
> @@ -1746,11 +1746,11 @@ static void rcu_gp_cleanup(struct rcu_state *rsp)
> needgp = __note_gp_changes(rsp, rnp, rdp) || needgp;
> /* smp_mb() provided by prior unlock-lock pair. */
> nocb += rcu_future_gp_cleanup(rsp, rnp);
> - raw_spin_unlock_irq(&rnp->lock);
> + raw_spin_unlock_irqrestore(&rnp->lock, flags);
> cond_resched();
> }
> rnp = rcu_get_root(rsp);
> - raw_spin_lock_irq(&rnp->lock);
> + raw_spin_lock_irqsave(&rnp->lock, flags);
> smp_mb__after_unlock_lock(); /* Order GP before ->completed update. */
> rcu_nocb_gp_set(rnp, nocb);
>
> @@ -1767,7 +1767,7 @@ static void rcu_gp_cleanup(struct rcu_state *rsp)
> ACCESS_ONCE(rsp->gpnum),
> TPS("newreq"));
> }
> - raw_spin_unlock_irq(&rnp->lock);
> + raw_spin_unlock_irqrestore(&rnp->lock, flags);
> }
>
> /*
> --
> 2.0.0.rc2
>
next prev parent reply other threads:[~2014-07-23 12:16 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-07-23 5:09 [PATCH 00/16] rcu: Some minor fixes and cleanups Pranith Kumar
2014-07-23 5:09 ` [PATCH 01/16] rcu: Use rcu_num_nodes instead of NUM_RCU_NODES Pranith Kumar
2014-07-23 5:09 ` [PATCH 02/16] rcu: Check return value for cpumask allocation Pranith Kumar
2014-07-23 12:06 ` Paul E. McKenney
2014-07-23 12:49 ` Pranith Kumar
2014-07-23 17:14 ` Pranith Kumar
2014-07-23 18:01 ` Paul E. McKenney
2014-07-23 5:09 ` [PATCH 03/16] rcu: Fix comment for gp_state field values Pranith Kumar
2014-07-23 5:09 ` [PATCH 04/16] rcu: Remove redundant check for an online CPU Pranith Kumar
2014-07-23 12:09 ` Paul E. McKenney
2014-07-23 13:23 ` Pranith Kumar
2014-07-23 13:41 ` Paul E. McKenney
2014-07-23 14:01 ` Pranith Kumar
2014-07-23 14:14 ` Paul E. McKenney
2014-07-23 15:07 ` Pranith Kumar
2014-07-23 15:21 ` Pranith Kumar
2014-07-23 5:09 ` [PATCH 05/16] rcu: Add noreturn attribute to boost kthread Pranith Kumar
2014-07-23 5:09 ` [PATCH 06/16] rcu: Clear gp_flags only when actually starting new gp Pranith Kumar
2014-07-23 12:13 ` Paul E. McKenney
2014-07-23 5:09 ` [PATCH 07/16] rcu: Save and restore irq flags in rcu_gp_cleanup() Pranith Kumar
2014-07-23 12:16 ` Paul E. McKenney [this message]
2014-07-23 5:09 ` [PATCH 08/16] rcu: Clean up rcu_spawn_one_boost_kthread() Pranith Kumar
2014-07-23 5:09 ` [PATCH 09/16] rcu: Remove redundant check for online cpu Pranith Kumar
2014-07-23 12:21 ` Paul E. McKenney
2014-07-23 12:59 ` Pranith Kumar
2014-07-23 13:50 ` Paul E. McKenney
2014-07-23 14:12 ` Pranith Kumar
2014-07-23 14:23 ` Paul E. McKenney
2014-07-23 15:11 ` Pranith Kumar
2014-07-23 15:30 ` Paul E. McKenney
2014-07-23 15:44 ` Pranith Kumar
2014-07-23 19:15 ` Paul E. McKenney
2014-07-23 20:01 ` Pranith Kumar
2014-07-23 20:16 ` Pranith Kumar
2014-07-23 20:23 ` Paul E. McKenney
2014-07-23 5:09 ` [PATCH 10/16] rcu: Check for RCU_FLAG_GP_INIT bit in gp_flags for spurious wakeup Pranith Kumar
2014-07-23 12:23 ` Paul E. McKenney
2014-07-23 5:09 ` [PATCH 11/16] rcu: Check for spurious wakeup using return value Pranith Kumar
2014-07-23 12:26 ` Paul E. McKenney
2014-07-24 2:36 ` Pranith Kumar
2014-07-24 3:43 ` Paul E. McKenney
2014-07-24 4:03 ` Pranith Kumar
2014-07-24 18:12 ` Paul E. McKenney
2014-07-24 19:59 ` Pranith Kumar
2014-07-24 20:27 ` Paul E. McKenney
2014-07-23 5:09 ` [PATCH 12/16] rcu: Rename rcu_spawn_gp_kthread() to rcu_spawn_kthreads() Pranith Kumar
2014-07-23 5:09 ` [PATCH 13/16] rcu: Spawn nocb kthreads from rcu_prepare_kthreads() Pranith Kumar
2014-07-23 5:09 ` [PATCH 14/16] rcu: Remove redundant checks for rcu_scheduler_fully_active Pranith Kumar
2014-07-23 12:27 ` Paul E. McKenney
2014-07-23 5:09 ` [PATCH 15/16] rcu: Check for a nocb cpu before trying to spawn nocb threads Pranith Kumar
2014-07-23 12:28 ` Paul E. McKenney
2014-07-23 13:14 ` Pranith Kumar
2014-07-23 13:42 ` Paul E. McKenney
2014-07-23 5:09 ` [PATCH 16/16] rcu: kvm.sh: Fix error when you pass --cpus argument Pranith Kumar
2014-07-23 12:31 ` Paul E. McKenney
2014-07-23 14:45 ` [PATCH 00/16] rcu: Some minor fixes and cleanups Paul E. McKenney
2014-08-27 1:10 ` Pranith Kumar
2014-08-27 3:20 ` Paul E. McKenney
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