From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756226Ab2ICJbP (ORCPT ); Mon, 3 Sep 2012 05:31:15 -0400 Received: from relay3-d.mail.gandi.net ([217.70.183.195]:35608 "EHLO relay3-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756085Ab2ICJbM (ORCPT ); Mon, 3 Sep 2012 05:31:12 -0400 X-Originating-IP: 217.70.178.139 X-Originating-IP: 50.43.46.74 Date: Mon, 3 Sep 2012 02:31:05 -0700 From: Josh Triplett To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, eric.dumazet@gmail.com, darren@dvhart.com, fweisbec@gmail.com, sbw@mit.edu, patches@linaro.org, "Paul E. McKenney" Subject: Re: [PATCH tip/core/rcu 13/23] rcu: Control grace-period duration from sysfs Message-ID: <20120903093104.GB5574@leaf> References: <20120830181811.GA29154@linux.vnet.ibm.com> <1346350718-30937-1-git-send-email-paulmck@linux.vnet.ibm.com> <1346350718-30937-13-git-send-email-paulmck@linux.vnet.ibm.com> <20120903093016.GA5574@leaf> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120903093016.GA5574@leaf> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Sep 03, 2012 at 02:30:16AM -0700, Josh Triplett wrote: > On Thu, Aug 30, 2012 at 11:18:28AM -0700, Paul E. McKenney wrote: > > From: "Paul E. McKenney" > > > > Some uses of RCU benefit from shorter grace periods, while others benefit > > more from the greater efficiency provided by longer grace periods. > > Therefore, this commit allows the durations to be controlled from sysfs. > > There are two sysfs parameters, one named "jiffies_till_first_fqs" that > > specifies the delay in jiffies from the end of grace-period initialization > > until the first attempt to force quiescent states, and the other named > > "jiffies_till_next_fqs" that specifies the delay (again in jiffies) > > between subsequent attempts to force quiescent states. They both default > > to three jiffies, which is compatible with the old hard-coded behavior. > > > > Signed-off-by: Paul E. McKenney > > Signed-off-by: Paul E. McKenney > > Signed-off-by: Josh Triplett Er, sorry, typo: Reviewed-by: Josh Triplett > > Documentation/kernel-parameters.txt | 11 +++++++++++ > > kernel/rcutree.c | 25 ++++++++++++++++++++++--- > > 2 files changed, 33 insertions(+), 3 deletions(-) > > > > diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt > > index ad7e2e5..55ada04 100644 > > --- a/Documentation/kernel-parameters.txt > > +++ b/Documentation/kernel-parameters.txt > > @@ -2385,6 +2385,17 @@ bytes respectively. Such letter suffixes can also be entirely omitted. > > rcutree.rcu_cpu_stall_timeout= [KNL,BOOT] > > Set timeout for RCU CPU stall warning messages. > > > > + rcutree.jiffies_till_first_fqs= [KNL,BOOT] > > + Set delay from grace-period initialization to > > + first attempt to force quiescent states. > > + Units are jiffies, minimum value is zero, > > + and maximum value is HZ. > > + > > + rcutree.jiffies_till_next_fqs= [KNL,BOOT] > > + Set delay between subsequent attempts to force > > + quiescent states. Units are jiffies, minimum > > + value is one, and maximum value is HZ. > > + > > rcutorture.fqs_duration= [KNL,BOOT] > > Set duration of force_quiescent_state bursts. > > > > diff --git a/kernel/rcutree.c b/kernel/rcutree.c > > index ed1be62..1d33240 100644 > > --- a/kernel/rcutree.c > > +++ b/kernel/rcutree.c > > @@ -226,6 +226,12 @@ int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT; > > module_param(rcu_cpu_stall_suppress, int, 0644); > > module_param(rcu_cpu_stall_timeout, int, 0644); > > > > +static ulong jiffies_till_first_fqs = RCU_JIFFIES_TILL_FORCE_QS; > > +static ulong jiffies_till_next_fqs = RCU_JIFFIES_TILL_FORCE_QS; > > + > > +module_param(jiffies_till_first_fqs, ulong, 0644); > > +module_param(jiffies_till_next_fqs, ulong, 0644); > > + > > static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *)); > > static void force_quiescent_state(struct rcu_state *rsp); > > static int rcu_pending(int cpu); > > @@ -1193,6 +1199,7 @@ static void rcu_gp_cleanup(struct rcu_state *rsp) > > static int rcu_gp_kthread(void *arg) > > { > > int fqs_state; > > + unsigned long j; > > int ret; > > struct rcu_state *rsp = arg; > > struct rcu_node *rnp = rcu_get_root(rsp); > > @@ -1213,14 +1220,18 @@ static int rcu_gp_kthread(void *arg) > > > > /* Handle quiescent-state forcing. */ > > fqs_state = RCU_SAVE_DYNTICK; > > + j = jiffies_till_first_fqs; > > + if (j > HZ) { > > + j = HZ; > > + jiffies_till_first_fqs = HZ; > > + } > > for (;;) { > > - rsp->jiffies_force_qs = jiffies + > > - RCU_JIFFIES_TILL_FORCE_QS; > > + rsp->jiffies_force_qs = jiffies + j; > > ret = wait_event_interruptible_timeout(rsp->gp_wq, > > (rsp->gp_flags & RCU_GP_FLAG_FQS) || > > (!ACCESS_ONCE(rnp->qsmask) && > > !rcu_preempt_blocked_readers_cgp(rnp)), > > - RCU_JIFFIES_TILL_FORCE_QS); > > + j); > > /* If grace period done, leave loop. */ > > if (!ACCESS_ONCE(rnp->qsmask) && > > !rcu_preempt_blocked_readers_cgp(rnp)) > > @@ -1234,6 +1245,14 @@ static int rcu_gp_kthread(void *arg) > > cond_resched(); > > flush_signals(current); > > } > > + j = jiffies_till_next_fqs; > > + if (j > HZ) { > > + j = HZ; > > + jiffies_till_next_fqs = HZ; > > + } else if (j < 1) { > > + j = 1; > > + jiffies_till_next_fqs = 1; > > + } > > } > > > > /* Handle grace-period end. */ > > -- > > 1.7.8 > >