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Date: Wed, 11 Sep 2013 15:34:57 +0200
From: Mike Galbraith <bitbucket@...ine.de>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Andy Lutomirski <luto@...capital.net>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Ingo Molnar <mingo@...nel.org>,
Andi Kleen <ak@...ux.intel.com>, Peter Anvin <hpa@...or.com>,
Thomas Gleixner <tglx@...utronix.de>,
Arjan van de Ven <arjan@...ux.intel.com>,
Frederic Weisbecker <fweisbec@...il.com>,
linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
Len Brown <lenb@...nel.org>,
Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
Subject: Re: [PATCH 2/7] sched: Add NEED_RESCHED to the preempt_count
On Wed, 2013-09-11 at 13:06 +0200, Peter Zijlstra wrote:
> On Wed, Sep 11, 2013 at 10:25:30AM +0200, Peter Zijlstra wrote:
> > On Tue, Sep 10, 2013 at 06:59:57PM -0700, Andy Lutomirski wrote:
>
> > > It looks like the intel_idle code can get confused if TIF_NEED_RESCHED
> > > is set but the preempt resched bit is not -- the need_resched call
> > > between monitor and mwait won't notice TIF_NEED_RESCHED.
> > >
> > > Is this condition possible?
> >
> > Ah indeed, I'll have to go find all idle loops out there it seems. Now
> > if only they were easy to spot :/
> >
> > I was hoping the generic idle thing was good enough, apparently not
> > quite. Thanks for spotting that.
>
> OK, and the reason I didn't notice is that the entire TS_POLLING thing
> is completely wrecked so we'll get the interrupt anyway.
>
> The below might fix it.. it boots, but then it already did so that
> doesn't say much.
>
> Mike does it fix the funny you saw?
Yup, modulo test_need_resched() not existing in master.
E5620 pipe-test
v3.7.10 578.5 KHz
v3.7.10-nothrottle 366.7 KHz
v3.8.13 468.3 KHz
v3.9.11 462.0 KHz
v3.10.4 419.4 KHz
v3.11-rc3-4-g36f571e 400.1 KHz
master-9013-gbf83e61 553.5 KHz
I still have your not quite complete hrtimer patch in there, lest menu
governor munch any improvement, as well as my throttle-nohz patch, so
seems we may be a _bit_ down vs 3.7, but reschedule_interrupt did crawl
back under its rock, and while I haven't yet booted Q6600 box, core2
Toshiba Satellite lappy is using mwait_idle_with_hints() in master.
Thanks,
-Mike
> ---
> Subject: sched, idle: Fix the idle polling state logic
> From: Peter Zijlstra <peterz@...radead.org>
> Date: Wed Sep 11 12:43:13 CEST 2013
>
> Mike reported that commit 7d1a9417 ("x86: Use generic idle loop")
> regressed several workloads and caused excessive reschedule
> interrupts.
>
> The patch in question failed to notice that the x86 code had an
> inverted sense of the polling state versus the new generic code (x86:
> default polling, generic: default !polling).
>
> Fix the two prominent x86 mwait based idle drivers and introduce a few
> new generic polling helpers (fixing the wrong smp_mb__after_clear_bit
> usage).
>
> Also switch the idle routines to using test_need_resched() which is an
> immediate TIF_NEED_RESCHED test as opposed to need_resched which will
> end up being slightly different.
>
> Reported-by: Mike Galbraith <bitbucket@...ine.de>
> Signed-off-by: Peter Zijlstra <peterz@...radead.org>
> ---
> arch/x86/kernel/process.c | 6 +--
> drivers/acpi/processor_idle.c | 46 +++++-------------------
> drivers/idle/intel_idle.c | 2 -
> include/linux/sched.h | 78 ++++++++++++++++++++++++++++++++++++++----
> kernel/cpu/idle.c | 9 ++--
> 5 files changed, 89 insertions(+), 52 deletions(-)
>
> --- a/arch/x86/kernel/process.c
> +++ b/arch/x86/kernel/process.c
> @@ -391,9 +391,9 @@ static void amd_e400_idle(void)
> * The switch back from broadcast mode needs to be
> * called with interrupts disabled.
> */
> - local_irq_disable();
> - clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT, &cpu);
> - local_irq_enable();
> + local_irq_disable();
> + clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT, &cpu);
> + local_irq_enable();
> } else
> default_idle();
> }
> --- a/drivers/acpi/processor_idle.c
> +++ b/drivers/acpi/processor_idle.c
> @@ -119,17 +119,10 @@ static struct dmi_system_id processor_po
> */
> static void acpi_safe_halt(void)
> {
> - current_thread_info()->status &= ~TS_POLLING;
> - /*
> - * TS_POLLING-cleared state must be visible before we
> - * test NEED_RESCHED:
> - */
> - smp_mb();
> - if (!need_resched()) {
> + if (!test_need_resched()) {
> safe_halt();
> local_irq_disable();
> }
> - current_thread_info()->status |= TS_POLLING;
> }
>
> #ifdef ARCH_APICTIMER_STOPS_ON_C3
> @@ -737,6 +730,11 @@ static int acpi_idle_enter_c1(struct cpu
> if (unlikely(!pr))
> return -EINVAL;
>
> + if (cx->entry_method == ACPI_CSTATE_FFH) {
> + if (current_set_polling_and_test())
> + return -EINVAL;
> + }
> +
> lapic_timer_state_broadcast(pr, cx, 1);
> acpi_idle_do_entry(cx);
>
> @@ -790,18 +788,9 @@ static int acpi_idle_enter_simple(struct
> if (unlikely(!pr))
> return -EINVAL;
>
> - if (cx->entry_method != ACPI_CSTATE_FFH) {
> - current_thread_info()->status &= ~TS_POLLING;
> - /*
> - * TS_POLLING-cleared state must be visible before we test
> - * NEED_RESCHED:
> - */
> - smp_mb();
> -
> - if (unlikely(need_resched())) {
> - current_thread_info()->status |= TS_POLLING;
> + if (cx->entry_method == ACPI_CSTATE_FFH) {
> + if (current_set_polling_and_test())
> return -EINVAL;
> - }
> }
>
> /*
> @@ -819,9 +808,6 @@ static int acpi_idle_enter_simple(struct
>
> sched_clock_idle_wakeup_event(0);
>
> - if (cx->entry_method != ACPI_CSTATE_FFH)
> - current_thread_info()->status |= TS_POLLING;
> -
> lapic_timer_state_broadcast(pr, cx, 0);
> return index;
> }
> @@ -858,18 +844,9 @@ static int acpi_idle_enter_bm(struct cpu
> }
> }
>
> - if (cx->entry_method != ACPI_CSTATE_FFH) {
> - current_thread_info()->status &= ~TS_POLLING;
> - /*
> - * TS_POLLING-cleared state must be visible before we test
> - * NEED_RESCHED:
> - */
> - smp_mb();
> -
> - if (unlikely(need_resched())) {
> - current_thread_info()->status |= TS_POLLING;
> + if (cx->entry_method == ACPI_CSTATE_FFH) {
> + if (current_set_polling_and_test())
> return -EINVAL;
> - }
> }
>
> acpi_unlazy_tlb(smp_processor_id());
> @@ -915,9 +892,6 @@ static int acpi_idle_enter_bm(struct cpu
>
> sched_clock_idle_wakeup_event(0);
>
> - if (cx->entry_method != ACPI_CSTATE_FFH)
> - current_thread_info()->status |= TS_POLLING;
> -
> lapic_timer_state_broadcast(pr, cx, 0);
> return index;
> }
> --- a/drivers/idle/intel_idle.c
> +++ b/drivers/idle/intel_idle.c
> @@ -359,7 +359,7 @@ static int intel_idle(struct cpuidle_dev
> if (!(lapic_timer_reliable_states & (1 << (cstate))))
> clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER, &cpu);
>
> - if (!need_resched()) {
> + if (!current_set_polling_and_test()) {
>
> __monitor((void *)¤t_thread_info()->flags, 0, 0);
> smp_mb();
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -2471,34 +2471,98 @@ static inline int tsk_is_polling(struct
> {
> return task_thread_info(p)->status & TS_POLLING;
> }
> -static inline void current_set_polling(void)
> +static inline void __current_set_polling(void)
> {
> current_thread_info()->status |= TS_POLLING;
> }
>
> -static inline void current_clr_polling(void)
> +static inline bool __must_check current_set_polling_and_test(void)
> +{
> + __current_set_polling();
> +
> + /*
> + * Polling state must be visible before we test NEED_RESCHED,
> + * paired by resched_task()
> + */
> + smp_mb();
> +
> + return unlikely(test_need_resched());
> +}
> +
> +static inline void __current_clr_polling(void)
> {
> current_thread_info()->status &= ~TS_POLLING;
> - smp_mb__after_clear_bit();
> +}
> +
> +static inline bool __must_check current_clr_polling_and_test(void)
> +{
> + __current_clr_polling();
> +
> + /*
> + * Polling state must be visible before we test NEED_RESCHED,
> + * paired by resched_task()
> + */
> + smp_mb();
> +
> + return unlikely(test_need_resched());
> }
> #elif defined(TIF_POLLING_NRFLAG)
> static inline int tsk_is_polling(struct task_struct *p)
> {
> return test_tsk_thread_flag(p, TIF_POLLING_NRFLAG);
> }
> -static inline void current_set_polling(void)
> +
> +static inline void __current_set_polling(void)
> {
> set_thread_flag(TIF_POLLING_NRFLAG);
> }
>
> -static inline void current_clr_polling(void)
> +static inline bool __must_check current_set_polling_and_test(void)
> +{
> + __current_set_polling();
> +
> + /*
> + * Polling state must be visible before we test NEED_RESCHED,
> + * paired by resched_task()
> + *
> + * XXX: assumes set/clear bit are identical barrier wise.
> + */
> + smp_mb__after_clear_bit();
> +
> + return unlikely(test_need_resched());
> +}
> +
> +static inline void __current_clr_polling(void)
> {
> clear_thread_flag(TIF_POLLING_NRFLAG);
> }
> +
> +static inline bool __must_check current_clr_polling_and_test(void)
> +{
> + __current_clr_polling();
> +
> + /*
> + * Polling state must be visible before we test NEED_RESCHED,
> + * paired by resched_task()
> + */
> + smp_mb__after_clear_bit();
> +
> + return unlikely(test_need_resched());
> +}
> +
> #else
> static inline int tsk_is_polling(struct task_struct *p) { return 0; }
> -static inline void current_set_polling(void) { }
> -static inline void current_clr_polling(void) { }
> +static inline void __current_set_polling(void) { }
> +static inline void __current_clr_polling(void) { }
> +
> +static inline bool __must_check current_set_polling_and_test(void)
> +{
> + return unlikely(test_need_resched);
> +}
> +static inline bool __must_check current_clr_polling_and_test(void)
> +{
> + return unlikely(test_need_resched);
> +}
> #endif
>
> /*
> --- a/kernel/cpu/idle.c
> +++ b/kernel/cpu/idle.c
> @@ -44,7 +44,7 @@ static inline int cpu_idle_poll(void)
> rcu_idle_enter();
> trace_cpu_idle_rcuidle(0, smp_processor_id());
> local_irq_enable();
> - while (!need_resched())
> + while (!test_need_resched())
> cpu_relax();
> trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, smp_processor_id());
> rcu_idle_exit();
> @@ -92,8 +92,7 @@ static void cpu_idle_loop(void)
> if (cpu_idle_force_poll || tick_check_broadcast_expired()) {
> cpu_idle_poll();
> } else {
> - current_clr_polling();
> - if (!need_resched()) {
> + if (!current_clr_polling_and_test()) {
> stop_critical_timings();
> rcu_idle_enter();
> arch_cpu_idle();
> @@ -103,7 +102,7 @@ static void cpu_idle_loop(void)
> } else {
> local_irq_enable();
> }
> - current_set_polling();
> + __current_set_polling();
> }
> arch_cpu_idle_exit();
> /*
> @@ -136,7 +135,7 @@ void cpu_startup_entry(enum cpuhp_state
> */
> boot_init_stack_canary();
> #endif
> - current_set_polling();
> + __current_set_polling();
> arch_cpu_idle_prepare();
> cpu_idle_loop();
> }
> --
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