From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751554AbaFMBfX (ORCPT ); Thu, 12 Jun 2014 21:35:23 -0400 Received: from e33.co.us.ibm.com ([32.97.110.151]:55965 "EHLO e33.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751058AbaFMBfW (ORCPT ); Thu, 12 Jun 2014 21:35:22 -0400 Date: Thu, 12 Jun 2014 18:35:15 -0700 From: "Paul E. McKenney" To: Frederic Weisbecker Cc: LKML , Josh Triplett , Steven Rostedt , Mathieu Desnoyers Subject: Re: [PATCH] rcu: Only pin GP kthread when full dynticks is actually used Message-ID: <20140613013515.GA9589@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1402618619-32630-1-git-send-email-fweisbec@gmail.com> <20140613012432.GH4581@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140613012432.GH4581@linux.vnet.ibm.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14061301-0928-0000-0000-0000029E0893 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 12, 2014 at 06:24:32PM -0700, Paul E. McKenney wrote: > On Fri, Jun 13, 2014 at 02:16:59AM +0200, Frederic Weisbecker wrote: > > CONFIG_NO_HZ_FULL may be enabled widely on distros nowadays but actual > > users should be a tiny minority, if actually any. > > > > Also there is a risk that affining the GP kthread to a single CPU could > > end up noticeably reducing RCU performances and increasing energy > > consumption. > > > > So lets affine the GP kthread only when nohz full is actually used > > (ie: when the nohz_full= parameter is filled or CONFIG_NO_HZ_FULL_ALL=y) Which reminds me... Kernel-heavy workloads running NO_HZ_FULL_ALL=y can see long RCU grace periods, as in about two seconds each. It is not hard for me to detect this situation. Is there some way I can call for a given CPU's scheduling-clock interrupt to be turned on? I believe that the nsproxy guys were seeing something like this as well. Thanx, Paul > > Signed-off-by: Frederic Weisbecker > > Cc: Josh Triplett > > Cc: Steven Rostedt > > Cc: Mathieu Desnoyers > > --- > > kernel/rcu/tree_plugin.h | 10 +++++++--- > > 1 file changed, 7 insertions(+), 3 deletions(-) > > > > diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h > > index cbc2c45..726f52c 100644 > > --- a/kernel/rcu/tree_plugin.h > > +++ b/kernel/rcu/tree_plugin.h > > @@ -2843,12 +2843,16 @@ static bool rcu_nohz_full_cpu(struct rcu_state *rsp) > > */ > > static void rcu_bind_gp_kthread(void) > > { > > -#ifdef CONFIG_NO_HZ_FULL > > - int cpu = ACCESS_ONCE(tick_do_timer_cpu); > > + int cpu; > > + > > + if (!tick_nohz_full_enabled()) > > + return; > > + > > + cpu = ACCESS_ONCE(tick_do_timer_cpu); > > > > if (cpu < 0 || cpu >= nr_cpu_ids) > > return; > > + > > if (raw_smp_processor_id() != cpu) > > set_cpus_allowed_ptr(current, cpumask_of(cpu)); > > -#endif /* #ifdef CONFIG_NO_HZ_FULL */ > > } > > Hello, Frederic, > > I have the following queued. Shall I port yours on top of mine, or is > there an issue with mine? > > Thanx, Paul > > ------------------------------------------------------------------------ > > rcu: Bind grace-period kthreads to non-NO_HZ_FULL CPUs > > Binding the grace-period kthreads to the timekeeping CPU resulted in > significant performance decreases for some workloads. For more detail, > see: > > https://lkml.org/lkml/2014/6/3/395 for benchmark numbers > > https://lkml.org/lkml/2014/6/4/218 for CPU statistics > > It turns out that it is necessary to bind the grace-period kthreads > to the timekeeping CPU only when all but CPU 0 is a nohz_full CPU > on the one hand or if CONFIG_NO_HZ_FULL_SYSIDLE=y on the other. > In other cases, it suffices to bind the grace-period kthreads to the > set of non-nohz_full CPUs. > > This commit therefore creates a tick_nohz_not_full_mask that is the > complement of tick_nohz_full_mask, and then binds the grace-period > kthread to the set of CPUs indicated by this new mask, which covers > the CONFIG_NO_HZ_FULL_SYSIDLE=n case. The CONFIG_NO_HZ_FULL_SYSIDLE=y > case still binds the grace-period kthreads to the timekeeping CPU. > > Reported-by: Jet Chen > Signed-off-by: Paul E. McKenney > > diff --git a/include/linux/tick.h b/include/linux/tick.h > index b84773cb9f4c..1fe0c05eee39 100644 > --- a/include/linux/tick.h > +++ b/include/linux/tick.h > @@ -162,6 +162,7 @@ static inline u64 get_cpu_iowait_time_us(int cpu, u64 *unused) { return -1; } > #ifdef CONFIG_NO_HZ_FULL > extern bool tick_nohz_full_running; > extern cpumask_var_t tick_nohz_full_mask; > +extern cpumask_var_t tick_nohz_not_full_mask; > > static inline bool tick_nohz_full_enabled(void) > { > diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h > index 7ce734040a5e..ec7627becaf0 100644 > --- a/kernel/rcu/tree_plugin.h > +++ b/kernel/rcu/tree_plugin.h > @@ -2863,7 +2863,12 @@ static void rcu_bind_gp_kthread(void) > > if (cpu < 0 || cpu >= nr_cpu_ids) > return; > +#ifdef CONFIG_NO_HZ_FULL_SYSIDLE > if (raw_smp_processor_id() != cpu) > set_cpus_allowed_ptr(current, cpumask_of(cpu)); > +#else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */ > + if (!cpumask_test_cpu(raw_smp_processor_id(), tick_nohz_not_full_mask)) > + set_cpus_allowed_ptr(current, tick_nohz_not_full_mask); > +#endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */ > #endif /* #ifdef CONFIG_NO_HZ_FULL */ > } > diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c > index 9f8af69c67ec..02209e957e76 100644 > --- a/kernel/time/tick-sched.c > +++ b/kernel/time/tick-sched.c > @@ -151,6 +151,7 @@ static void tick_sched_handle(struct tick_sched *ts, struct pt_regs *regs) > > #ifdef CONFIG_NO_HZ_FULL > cpumask_var_t tick_nohz_full_mask; > +cpumask_var_t tick_nohz_not_full_mask; > bool tick_nohz_full_running; > > static bool can_stop_full_tick(void) > @@ -278,6 +279,7 @@ static int __init tick_nohz_full_setup(char *str) > int cpu; > > alloc_bootmem_cpumask_var(&tick_nohz_full_mask); > + alloc_bootmem_cpumask_var(&tick_nohz_not_full_mask); > if (cpulist_parse(str, tick_nohz_full_mask) < 0) { > pr_warning("NOHZ: Incorrect nohz_full cpumask\n"); > return 1; > @@ -288,6 +290,8 @@ static int __init tick_nohz_full_setup(char *str) > pr_warning("NO_HZ: Clearing %d from nohz_full range for timekeeping\n", cpu); > cpumask_clear_cpu(cpu, tick_nohz_full_mask); > } > + cpumask_andnot(tick_nohz_not_full_mask, > + cpu_possible_mask, tick_nohz_full_mask); > tick_nohz_full_running = true; > > return 1; > @@ -332,6 +336,8 @@ static int tick_nohz_init_all(void) > err = 0; > cpumask_setall(tick_nohz_full_mask); > cpumask_clear_cpu(smp_processor_id(), tick_nohz_full_mask); > + cpumask_clear(tick_nohz_not_full_mask); > + cpumask_set_cpu(smp_processor_id(), tick_nohz_not_full_mask); > tick_nohz_full_running = true; > #endif > return err;