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Date: Thu, 17 Nov 2011 17:03:44 -0800
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: Josh Triplett <josh@...htriplett.org>
Cc: Frederic Weisbecker <fweisbec@...il.com>,
LKML <linux-kernel@...r.kernel.org>,
Ingo Molnar <mingo@...hat.com>,
Thomas Gleixner <tglx@...utronix.de>,
Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] nohz: Remove tick_nohz_idle_enter_norcu() /
tick_nohz_idle_exit_norcu()
On Thu, Nov 17, 2011 at 12:11:34PM -0800, Josh Triplett wrote:
> 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 <fweisbec@...il.com>
> > Cc: Ingo Molnar <mingo@...hat.com>
> > Cc: Thomas Gleixner <tglx@...utronix.de>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Cc: Josh Triplett <josh@...htriplett.org>
>
> Reviewed-by: Josh Triplett <josh@...htriplett.org>
Merged, thank you both!
Thanx, Paul
> > 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
> >
>
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