From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751409AbdAWU0I (ORCPT ); Mon, 23 Jan 2017 15:26:08 -0500 Received: from relay3-d.mail.gandi.net ([217.70.183.195]:49287 "EHLO relay3-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750705AbdAWU0H (ORCPT ); Mon, 23 Jan 2017 15:26:07 -0500 Date: Mon, 23 Jan 2017 12:25:59 -0800 From: Josh Triplett To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, dvhart@linux.intel.com, fweisbec@gmail.com, oleg@redhat.com, bobby.prani@gmail.com Subject: Re: [PATCH v2 tip/core/rcu 07/18] rcu: Add long-term CPU kicking Message-ID: <20170123202559.GA1007@cloud> References: <20170118025316.GB2042@linux.vnet.ibm.com> <1484708037-2523-7-git-send-email-paulmck@linux.vnet.ibm.com> <20170121204255.ojlqgfk6lh7lac76@x> <20170123193445.GI28085@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170123193445.GI28085@linux.vnet.ibm.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jan 23, 2017 at 11:34:45AM -0800, Paul E. McKenney wrote: > On Sat, Jan 21, 2017 at 12:42:55PM -0800, Josh Triplett wrote: > > On Tue, Jan 17, 2017 at 06:53:46PM -0800, Paul E. McKenney wrote: > > > Commit d2db185bfee8 ("rcu: Remove short-term CPU kicking") removed > > > frequent calls to resched_cpu(), which means that the only time > > > resched_cpu() is invoked is after an RCU CPU stall warning. Although > > > this is good from an avoid-IPIs perspective, we should try to break > > > things loose -before- splatting. This commit therefore starts invoking > > > resched_cpu() for each holdout at each force-quiescent-state interval > > > that is more than halfway through the stall-warning interval. > > > > Just realized an issue with this commit message: you're referring to > > what now appears as patch 8 in the past tense as something already done, > > and with a commit ID that probably doesn't work anymore. You need to > > rephrase this to describe how it leads to a *subsequent* change rather > > than fixing something already changed. > > > > With the commit message fixed: > > Reviewed-by: Josh Triplett > > Good point! It now reads as follows: > > ------------------------------------------------------------------------ > This commit prepares for the removal of short-term CPU kicking (in a > subsequent commit). It does so by starting to invoke resched_cpu() > for each holdout at each force-quiescent-state interval that is more > than halfway through the stall-warning interval. > ------------------------------------------------------------------------ > > Does that work? Looks good to me. > Thanx, Paul > > > > Signed-off-by: Paul E. McKenney > > > > > > > > > --- > > > kernel/rcu/tree.c | 6 ++++++ > > > 1 file changed, 6 insertions(+) > > > > > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > > > index 83bf054e194e..0e61b62e3f4a 100644 > > > --- a/kernel/rcu/tree.c > > > +++ b/kernel/rcu/tree.c > > > @@ -1225,6 +1225,12 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp, > > > rdp->rsp->gp_start + 2 * jiffies_till_sched_qs) || > > > ULONG_CMP_GE(jiffies, rdp->rsp->gp_start + jiffies_till_sched_qs)) > > > resched_cpu(rdp->cpu); /* Force CPU into scheduler. */ > > > + /* > > > + * If more than halfway to RCU CPU stall-warning time, do > > > + * a resched_cpu() to try to loosen things up a bit. > > > + */ > > > + if (jiffies - rdp->rsp->gp_start > rcu_jiffies_till_stall_check() / 2) > > > + resched_cpu(rdp->cpu); > > > > > > return 0; > > > } > > > -- > > > 2.5.2 > > > > > >