From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755758Ab1KQULp (ORCPT ); Thu, 17 Nov 2011 15:11:45 -0500 Received: from relay4-d.mail.gandi.net ([217.70.183.196]:42859 "EHLO relay4-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754203Ab1KQULo (ORCPT ); Thu, 17 Nov 2011 15:11:44 -0500 X-Originating-IP: 217.70.178.137 X-Originating-IP: 50.43.15.19 Date: Thu, 17 Nov 2011 12:11:34 -0800 From: Josh Triplett To: Frederic Weisbecker Cc: "Paul E. McKenney" , LKML , Ingo Molnar , Thomas Gleixner , Peter Zijlstra Subject: Re: [PATCH] nohz: Remove tick_nohz_idle_enter_norcu() / tick_nohz_idle_exit_norcu() Message-ID: <20111117201134.GB1865@leaf> References: <1321552094-20237-1-git-send-email-fweisbec@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1321552094-20237-1-git-send-email-fweisbec@gmail.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 Thu, Nov 17, 2011 at 06:48:14PM +0100, Frederic Weisbecker wrote: > Those two APIs were provided to optimize the calls of > tick_nohz_idle_enter() and rcu_idle_enter() into a single > irq disabled section. This way no interrupt happening in-between would > needlessly process any RCU job. > > Now we are talking about an optimization for which benefits > have yet to be measured. Let's start simple and completely decouple > idle rcu and dyntick idle logics to simplify. > > Signed-off-by: Frederic Weisbecker > Cc: Ingo Molnar > Cc: Thomas Gleixner > Cc: Peter Zijlstra > Cc: Josh Triplett Reviewed-by: Josh Triplett > diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c > index 4f83362..0e42a9c 100644 > --- a/arch/arm/kernel/process.c > +++ b/arch/arm/kernel/process.c > @@ -183,7 +183,8 @@ void cpu_idle(void) > > /* endless idle loop with no priority at all */ > while (1) { > - tick_nohz_idle_enter_norcu(); > + tick_nohz_idle_enter(); > + rcu_idle_enter(); > leds_event(led_idle_start); > while (!need_resched()) { > #ifdef CONFIG_HOTPLUG_CPU > @@ -210,7 +211,8 @@ void cpu_idle(void) > } > } > leds_event(led_idle_end); > - tick_nohz_idle_exit_norcu(); > + rcu_idle_exit(); > + tick_nohz_idle_exit(); > preempt_enable_no_resched(); > schedule(); > preempt_disable(); > diff --git a/arch/avr32/kernel/process.c b/arch/avr32/kernel/process.c > index 34c8c70..ea33957 100644 > --- a/arch/avr32/kernel/process.c > +++ b/arch/avr32/kernel/process.c > @@ -34,10 +34,12 @@ void cpu_idle(void) > { > /* endless idle loop with no priority at all */ > while (1) { > - tick_nohz_idle_enter_norcu(); > + tick_nohz_idle_enter(); > + rcu_idle_enter(); > while (!need_resched()) > cpu_idle_sleep(); > - tick_nohz_idle_exit_norcu(); > + rcu_idle_exit(); > + tick_nohz_idle_exit(); > preempt_enable_no_resched(); > schedule(); > preempt_disable(); > diff --git a/arch/blackfin/kernel/process.c b/arch/blackfin/kernel/process.c > index 57e0749..8dd0416 100644 > --- a/arch/blackfin/kernel/process.c > +++ b/arch/blackfin/kernel/process.c > @@ -88,10 +88,12 @@ void cpu_idle(void) > #endif > if (!idle) > idle = default_idle; > - tick_nohz_idle_enter_norcu(); > + tick_nohz_idle_enter(); > + rcu_idle_enter(); > while (!need_resched()) > idle(); > - tick_nohz_idle_exit_norcu(); > + rcu_idle_exit(); > + tick_nohz_idle_exit(); > preempt_enable_no_resched(); > schedule(); > preempt_disable(); > diff --git a/arch/microblaze/kernel/process.c b/arch/microblaze/kernel/process.c > index c6ece38..37ed945 100644 > --- a/arch/microblaze/kernel/process.c > +++ b/arch/microblaze/kernel/process.c > @@ -103,10 +103,12 @@ void cpu_idle(void) > if (!idle) > idle = default_idle; > > - tick_nohz_idle_enter_norcu(); > + tick_nohz_idle_enter(); > + rcu_idle_enter(); > while (!need_resched()) > idle(); > - tick_nohz_idle_exit_norcu(); > + rcu_idle_exit(); > + tick_nohz_idle_exit(); > > preempt_enable_no_resched(); > schedule(); > diff --git a/arch/mips/kernel/process.c b/arch/mips/kernel/process.c > index 7df2ffc..7937367 100644 > --- a/arch/mips/kernel/process.c > +++ b/arch/mips/kernel/process.c > @@ -56,7 +56,8 @@ void __noreturn cpu_idle(void) > > /* endless idle loop with no priority at all */ > while (1) { > - tick_nohz_idle_enter_norcu(); > + tick_nohz_idle_enter(); > + rcu_idle_enter(); > while (!need_resched() && cpu_online(cpu)) { > #ifdef CONFIG_MIPS_MT_SMTC > extern void smtc_idle_loop_hook(void); > @@ -77,7 +78,8 @@ void __noreturn cpu_idle(void) > system_state == SYSTEM_BOOTING)) > play_dead(); > #endif > - tick_nohz_idle_exit_norcu(); > + rcu_idle_exit(); > + tick_nohz_idle_exit(); > preempt_enable_no_resched(); > schedule(); > preempt_disable(); > diff --git a/arch/openrisc/kernel/idle.c b/arch/openrisc/kernel/idle.c > index 2e82cd0..e5fc7887 100644 > --- a/arch/openrisc/kernel/idle.c > +++ b/arch/openrisc/kernel/idle.c > @@ -51,7 +51,8 @@ void cpu_idle(void) > > /* endless idle loop with no priority at all */ > while (1) { > - tick_nohz_idle_enter_norcu(); > + tick_nohz_idle_enter(); > + rcu_idle_enter(); > > while (!need_resched()) { > check_pgt_cache(); > @@ -69,7 +70,8 @@ void cpu_idle(void) > set_thread_flag(TIF_POLLING_NRFLAG); > } > > - tick_nohz_idle_exit_norcu(); > + rcu_idle_exit(); > + tick_nohz_idle_exit(); > preempt_enable_no_resched(); > schedule(); > preempt_disable(); > diff --git a/arch/powerpc/kernel/idle.c b/arch/powerpc/kernel/idle.c > index 3cd73d1..9c3cd49 100644 > --- a/arch/powerpc/kernel/idle.c > +++ b/arch/powerpc/kernel/idle.c > @@ -62,10 +62,10 @@ void cpu_idle(void) > > set_thread_flag(TIF_POLLING_NRFLAG); > while (1) { > - if (idle_uses_rcu) > - tick_nohz_idle_enter(); > - else > - tick_nohz_idle_enter_norcu(); > + tick_nohz_idle_enter(); > + if (!idle_uses_rcu) > + rcu_idle_enter(); > + > while (!need_resched() && !cpu_should_die()) { > ppc64_runlatch_off(); > > @@ -102,10 +102,9 @@ void cpu_idle(void) > > HMT_medium(); > ppc64_runlatch_on(); > - if (idle_uses_rcu) > - tick_nohz_idle_exit(); > - else > - tick_nohz_idle_exit_norcu(); > + if (!idle_uses_rcu) > + rcu_idle_exit(); > + tick_nohz_idle_exit(); > preempt_enable_no_resched(); > if (cpu_should_die()) > cpu_die(); > diff --git a/arch/powerpc/platforms/iseries/setup.c b/arch/powerpc/platforms/iseries/setup.c > index 77ff6eb..097f7d5 100644 > --- a/arch/powerpc/platforms/iseries/setup.c > +++ b/arch/powerpc/platforms/iseries/setup.c > @@ -562,7 +562,8 @@ static void yield_shared_processor(void) > static void iseries_shared_idle(void) > { > while (1) { > - tick_nohz_idle_enter_norcu(); > + tick_nohz_idle_enter(); > + rcu_idle_enter(); > while (!need_resched() && !hvlpevent_is_pending()) { > local_irq_disable(); > ppc64_runlatch_off(); > @@ -576,7 +577,8 @@ static void iseries_shared_idle(void) > } > > ppc64_runlatch_on(); > - tick_nohz_idle_exit_norcu(); > + rcu_idle_exit(); > + tick_nohz_idle_exit(); > > if (hvlpevent_is_pending()) > process_iSeries_events(); > @@ -592,7 +594,8 @@ static void iseries_dedicated_idle(void) > set_thread_flag(TIF_POLLING_NRFLAG); > > while (1) { > - tick_nohz_idle_enter_norcu(); > + tick_nohz_idle_enter(); > + rcu_idle_enter(); > if (!need_resched()) { > while (!need_resched()) { > ppc64_runlatch_off(); > @@ -609,7 +612,8 @@ static void iseries_dedicated_idle(void) > } > > ppc64_runlatch_on(); > - tick_nohz_idle_exit_norcu(); > + rcu_idle_exit(); > + tick_nohz_idle_exit(); > preempt_enable_no_resched(); > schedule(); > preempt_disable(); > diff --git a/arch/s390/kernel/process.c b/arch/s390/kernel/process.c > index 44028ae..bf2bc31 100644 > --- a/arch/s390/kernel/process.c > +++ b/arch/s390/kernel/process.c > @@ -90,10 +90,12 @@ static void default_idle(void) > void cpu_idle(void) > { > for (;;) { > - tick_nohz_idle_enter_norcu(); > + tick_nohz_idle_enter(); > + rcu_idle_enter(); > while (!need_resched()) > default_idle(); > - tick_nohz_idle_exit_norcu(); > + rcu_idle_exit(); > + tick_nohz_idle_exit(); > preempt_enable_no_resched(); > schedule(); > preempt_disable(); > diff --git a/arch/sh/kernel/idle.c b/arch/sh/kernel/idle.c > index ad58e75..406508d 100644 > --- a/arch/sh/kernel/idle.c > +++ b/arch/sh/kernel/idle.c > @@ -89,7 +89,8 @@ void cpu_idle(void) > > /* endless idle loop with no priority at all */ > while (1) { > - tick_nohz_idle_enter_norcu(); > + tick_nohz_idle_enter(); > + rcu_idle_enter(); > > while (!need_resched()) { > check_pgt_cache(); > @@ -111,7 +112,8 @@ void cpu_idle(void) > start_critical_timings(); > } > > - tick_nohz_idle_exit_norcu(); > + rcu_idle_exit(); > + tick_nohz_idle_exit(); > preempt_enable_no_resched(); > schedule(); > preempt_disable(); > diff --git a/arch/sparc/kernel/process_64.c b/arch/sparc/kernel/process_64.c > index 78b1bc0..fde8d72 100644 > --- a/arch/sparc/kernel/process_64.c > +++ b/arch/sparc/kernel/process_64.c > @@ -95,12 +95,14 @@ void cpu_idle(void) > set_thread_flag(TIF_POLLING_NRFLAG); > > while(1) { > - tick_nohz_idle_enter_norcu(); > + tick_nohz_idle_enter(); > + rcu_idle_enter(); > > while (!need_resched() && !cpu_is_offline(cpu)) > sparc64_yield(cpu); > > - tick_nohz_idle_exit_norcu(); > + rcu_idle_exit(); > + tick_nohz_idle_exit(); > > preempt_enable_no_resched(); > > diff --git a/arch/tile/kernel/process.c b/arch/tile/kernel/process.c > index 53ac895..4c1ac6e 100644 > --- a/arch/tile/kernel/process.c > +++ b/arch/tile/kernel/process.c > @@ -85,7 +85,8 @@ void cpu_idle(void) > > /* endless idle loop with no priority at all */ > while (1) { > - tick_nohz_idle_enter_norcu(); > + tick_nohz_idle_enter(); > + rcu_idle_enter(); > while (!need_resched()) { > if (cpu_is_offline(cpu)) > BUG(); /* no HOTPLUG_CPU */ > @@ -105,7 +106,8 @@ void cpu_idle(void) > local_irq_enable(); > current_thread_info()->status |= TS_POLLING; > } > - tick_nohz_idle_exit_norcu(); > + rcu_idle_exit(); > + tick_nohz_idle_exit(); > preempt_enable_no_resched(); > schedule(); > preempt_disable(); > diff --git a/arch/um/kernel/process.c b/arch/um/kernel/process.c > index 9e7176b..b652ff1 100644 > --- a/arch/um/kernel/process.c > +++ b/arch/um/kernel/process.c > @@ -245,10 +245,12 @@ void default_idle(void) > if (need_resched()) > schedule(); > > - tick_nohz_idle_enter_norcu(); > + tick_nohz_idle_enter(); > + rcu_idle_enter(); > nsecs = disable_timer(); > idle_sleep(nsecs); > - tick_nohz_idle_exit_norcu(); > + rcu_idle_exit(); > + tick_nohz_idle_exit(); > } > } > > diff --git a/arch/unicore32/kernel/process.c b/arch/unicore32/kernel/process.c > index 095ff5a..52edc2b 100644 > --- a/arch/unicore32/kernel/process.c > +++ b/arch/unicore32/kernel/process.c > @@ -55,7 +55,8 @@ void cpu_idle(void) > { > /* endless idle loop with no priority at all */ > while (1) { > - tick_nohz_idle_enter_norcu(); > + tick_nohz_idle_enter(); > + rcu_idle_enter(); > while (!need_resched()) { > local_irq_disable(); > stop_critical_timings(); > @@ -63,7 +64,8 @@ void cpu_idle(void) > local_irq_enable(); > start_critical_timings(); > } > - tick_nohz_idle_exit_norcu(); > + rcu_idle_exit(); > + tick_nohz_idle_exit(); > preempt_enable_no_resched(); > schedule(); > preempt_disable(); > diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c > index f311d096..44e3384 100644 > --- a/arch/x86/kernel/process_32.c > +++ b/arch/x86/kernel/process_32.c > @@ -98,7 +98,8 @@ void cpu_idle(void) > > /* endless idle loop with no priority at all */ > while (1) { > - tick_nohz_idle_enter_norcu(); > + tick_nohz_idle_enter(); > + rcu_idle_enter(); > while (!need_resched()) { > > check_pgt_cache(); > @@ -114,7 +115,8 @@ void cpu_idle(void) > pm_idle(); > start_critical_timings(); > } > - tick_nohz_idle_exit_norcu(); > + rcu_idle_exit(); > + tick_nohz_idle_exit(); > preempt_enable_no_resched(); > schedule(); > preempt_disable(); > diff --git a/include/linux/tick.h b/include/linux/tick.h > index 327434a..ab8be90 100644 > --- a/include/linux/tick.h > +++ b/include/linux/tick.h > @@ -122,45 +122,8 @@ static inline int tick_oneshot_mode_active(void) { return 0; } > #endif /* !CONFIG_GENERIC_CLOCKEVENTS */ > > # ifdef CONFIG_NO_HZ > -extern void __tick_nohz_idle_enter(void); > -static inline void tick_nohz_idle_enter(void) > -{ > - local_irq_disable(); > - __tick_nohz_idle_enter(); > - local_irq_enable(); > -} > +extern void tick_nohz_idle_enter(void); > extern void tick_nohz_idle_exit(void); > - > -/* > - * Call this pair of function if the arch doesn't make any use > - * of RCU in-between. You won't need to call rcu_idle_enter() and > - * rcu_idle_exit(). > - * Otherwise you need to call tick_nohz_idle_enter() and tick_nohz_idle_exit() > - * and explicitly tell RCU about the window around the place the CPU enters low > - * power mode where no RCU use is made. This is done by calling rcu_idle_enter() > - * after the last use of RCU before the CPU is put to sleep and by calling > - * rcu_idle_exit() before the first use of RCU after the CPU woke up. > - */ > -static inline void tick_nohz_idle_enter_norcu(void) > -{ > - /* > - * Also call rcu_idle_enter() in the irq disabled section even > - * if it disables irq itself. > - * Just an optimization that prevents from an interrupt happening > - * between it and __tick_nohz_idle_enter() to lose time to help > - * completing a grace period while we could be in extended grace > - * period already. > - */ > - local_irq_disable(); > - __tick_nohz_idle_enter(); > - rcu_idle_enter(); > - local_irq_enable(); > -} > -static inline void tick_nohz_idle_exit_norcu(void) > -{ > - rcu_idle_exit(); > - tick_nohz_idle_exit(); > -} > extern void tick_nohz_irq_exit(void); > extern ktime_t tick_nohz_get_sleep_length(void); > extern u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time); > @@ -168,14 +131,6 @@ extern u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time); > # else > static inline void tick_nohz_idle_enter(void) { } > static inline void tick_nohz_idle_exit(void) { } > -static inline void tick_nohz_idle_enter_norcu(void) > -{ > - rcu_idle_enter(); > -} > -static inline void tick_nohz_idle_exit_norcu(void) > -{ > - rcu_idle_exit(); > -} > > static inline ktime_t tick_nohz_get_sleep_length(void) > { > diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c > index 360d028..0d887e8 100644 > --- a/kernel/time/tick-sched.c > +++ b/kernel/time/tick-sched.c > @@ -425,21 +425,20 @@ out: > * When the next event is more than a tick into the future, stop the idle tick > * Called when we start the idle loop. > * > - * If no use of RCU is made in the idle loop between > - * tick_nohz_idle_enter() and tick_nohz_idle_exit() calls, then > - * tick_nohz_idle_enter_norcu() should be called instead and the arch > - * doesn't need to call rcu_idle_enter() and rcu_idle_exit() explicitly. > - * > - * Otherwise the arch is responsible of calling: > + * The arch is responsible of calling: > * > * - rcu_idle_enter() after its last use of RCU before the CPU is put > * to sleep. > * - rcu_idle_exit() before the first use of RCU after the CPU is woken up. > */ > -void __tick_nohz_idle_enter(void) > +void tick_nohz_idle_enter(void) > { > struct tick_sched *ts; > > + WARN_ON_ONCE(irqs_disabled()); > + > + local_irq_disable(); > + > ts = &__get_cpu_var(tick_cpu_sched); > /* > * set ts->inidle unconditionally. even if the system did not > @@ -448,6 +447,8 @@ void __tick_nohz_idle_enter(void) > */ > ts->inidle = 1; > tick_nohz_stop_sched_tick(ts); > + > + local_irq_enable(); > } > > /** > -- > 1.7.5.4 >