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 09/16] rcu: Remove redundant check for online cpu
Date: Wed, 23 Jul 2014 06:50:24 -0700 [thread overview]
Message-ID: <20140723135024.GR11241@linux.vnet.ibm.com> (raw)
In-Reply-To: <CAJhHMCAoLQPnJYCeqftXwZb6D4ECuJb4g04b4OO5BLf6iC1ENw@mail.gmail.com>
On Wed, Jul 23, 2014 at 08:59:06AM -0400, Pranith Kumar wrote:
> On Wed, Jul 23, 2014 at 8:21 AM, Paul E. McKenney
> <paulmck@linux.vnet.ibm.com> wrote:
> > On Wed, Jul 23, 2014 at 01:09:46AM -0400, Pranith Kumar wrote:
> >> There are two checks for an online CPU if two if() conditions. This commit
> >> simplies this by replacing it with only one check for the online CPU.
> >>
> >> Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
> >
> > I admit that it is very early in the morning my time, but I don't see
> > this change as preserving the semantics in all cases. Please recheck
> > your changes to the second check.
> >
> > Thanx, Paul
>
> I guess you must be thrown off by the complementary checks, the first
> check is for cpu_online() and second is for cpu_is_offline(). :)
>
> Previously, if a cpu is offline, the first condition is false and the
> second condition is true, so we return from the second if() condition.
> The same semantics are being preserved.
Fair enough!
Nevertheless, I am not seeing this as a simplification.
Thanx, Paul
> --
> Pranith.
>
>
>
> >
> >> ---
> >> kernel/rcu/tree.c | 9 ++++++---
> >> 1 file changed, 6 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> >> index 5dcbf36..8d598a2 100644
> >> --- a/kernel/rcu/tree.c
> >> +++ b/kernel/rcu/tree.c
> >> @@ -2602,15 +2602,18 @@ static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp,
> >> {
> >> bool needwake;
> >>
> >> + if (!cpu_online(smp_processor_id()))
> >> + return;
> >> +
> >> /*
> >> * If called from an extended quiescent state, invoke the RCU
> >> * core in order to force a re-evaluation of RCU's idleness.
> >> */
> >> - if (!rcu_is_watching() && cpu_online(smp_processor_id()))
> >> + if (!rcu_is_watching())
> >> invoke_rcu_core();
> >>
> >> - /* If interrupts were disabled or CPU offline, don't invoke RCU core. */
> >> - if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id()))
> >> + /* If interrupts were disabled, don't invoke RCU core. */
> >> + if (irqs_disabled_flags(flags))
> >> return;
> >>
> >> /*
> >> --
> >> 2.0.0.rc2
> >>
> >
>
>
>
> --
> Pranith
>
next prev parent reply other threads:[~2014-07-23 13:50 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
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 [this message]
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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