Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754495AbaGHPYI (ORCPT ); Tue, 8 Jul 2014 11:24:08 -0400 Received: from mail-we0-f181.google.com ([74.125.82.181]:63383 "EHLO mail-we0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754452AbaGHPYE (ORCPT ); Tue, 8 Jul 2014 11:24:04 -0400 Date: Tue, 8 Jul 2014 17:24:00 +0200 From: Frederic Weisbecker To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, dvhart@linux.intel.com, oleg@redhat.com, sbw@mit.edu Subject: Re: [PATCH tip/core/rcu 11/17] rcu: Bind grace-period kthreads to non-NO_HZ_FULL CPUs Message-ID: <20140708152358.GF6571@localhost.localdomain> References: <20140707223756.GA7187@linux.vnet.ibm.com> <1404772701-8804-1-git-send-email-paulmck@linux.vnet.ibm.com> <1404772701-8804-11-git-send-email-paulmck@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1404772701-8804-11-git-send-email-paulmck@linux.vnet.ibm.com> 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, Jul 07, 2014 at 03:38:15PM -0700, Paul E. McKenney wrote: > From: "Paul E. McKenney" > > 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. > This commit also includes the tick_nohz_full_enabled() check suggested > by Frederic Weisbecker. > > Reported-by: Jet Chen > Signed-off-by: Paul E. McKenney > [ paulmck: Created housekeeping_affine() per fweisbec feedback. ] > --- > include/linux/tick.h | 19 +++++++++++++++++++ > kernel/rcu/tree_plugin.h | 14 +++++++++----- > kernel/time/tick-sched.c | 10 ++++++++++ > 3 files changed, 38 insertions(+), 5 deletions(-) > > diff --git a/include/linux/tick.h b/include/linux/tick.h > index b84773cb9f4c..c39af3261351 100644 > --- a/include/linux/tick.h > +++ b/include/linux/tick.h > @@ -12,6 +12,7 @@ > #include > #include > #include > +#include > > #ifdef CONFIG_GENERIC_CLOCKEVENTS > > @@ -162,6 +163,7 @@ 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; So I'm still puzzled by this mask. How about creating a temporary cpumask on top of tick_nohz_full_mask from housekeeping_affine(). If you wonder about performance, this can be called once for good from rcu_spawn_gp_kthread() (that would be much better than checking that all the time from the kthread itself anyway). In case you're out of time, I can handle that. Just checking your opinion. Thanks. > > static inline bool tick_nohz_full_enabled(void) > { > @@ -194,6 +196,23 @@ static inline void tick_nohz_full_kick_all(void) { } > static inline void __tick_nohz_task_switch(struct task_struct *tsk) { } > #endif > > +static inline bool is_housekeeping_cpu(int cpu) > +{ > +#ifdef CONFIG_NO_HZ_FULL > + if (tick_nohz_full_enabled()) > + return cpumask_test_cpu(cpu, tick_nohz_not_full_mask); > +#endif > + return true; > +} > + > +static inline void housekeeping_affine(struct task_struct *t) > +{ > +#ifdef CONFIG_NO_HZ_FULL > + if (tick_nohz_full_enabled()) > + set_cpus_allowed_ptr(t, tick_nohz_not_full_mask); > +#endif > +} > + > static inline void tick_nohz_full_check(void) > { > if (tick_nohz_full_enabled()) > diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h > index 719587af7b10..b39ba7239bd6 100644 > --- a/kernel/rcu/tree_plugin.h > +++ b/kernel/rcu/tree_plugin.h > @@ -2846,12 +2846,16 @@ static bool rcu_nohz_full_cpu(struct rcu_state *rsp) > */ > static void rcu_bind_gp_kthread(void) > { > -#ifdef CONFIG_NO_HZ_FULL > - int cpu = tick_do_timer_cpu; > + int __maybe_unused cpu; > > - if (cpu < 0 || cpu >= nr_cpu_ids) > + if (!tick_nohz_full_enabled()) > return; > - if (raw_smp_processor_id() != cpu) > +#ifdef CONFIG_NO_HZ_FULL_SYSIDLE > + cpu = tick_do_timer_cpu; > + if (cpu >= 0 && cpu < nr_cpu_ids && raw_smp_processor_id() != cpu) > set_cpus_allowed_ptr(current, cpumask_of(cpu)); > -#endif /* #ifdef CONFIG_NO_HZ_FULL */ > +#else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */ > + if (!is_housekeeping_cpu(raw_smp_processor_id())) > + housekeeping_affine(current); > +#endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */ > } > diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c > index 6558b7ac112d..e023134d63a1 100644 > --- a/kernel/time/tick-sched.c > +++ b/kernel/time/tick-sched.c > @@ -154,6 +154,7 @@ 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) > @@ -281,6 +282,7 @@ 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; > @@ -291,6 +293,8 @@ 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; > @@ -332,9 +336,15 @@ static int tick_nohz_init_all(void) > pr_err("NO_HZ: Can't allocate full dynticks cpumask\n"); > return err; > } > + if (!alloc_cpumask_var(&tick_nohz_not_full_mask, GFP_KERNEL)) { > + pr_err("NO_HZ: Can't allocate not-full dynticks cpumask\n"); > + return err; > + } > 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; > -- > 1.8.1.5 > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/