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Date: Mon, 21 Oct 2013 11:14:50 +0800
From: Yuanhan Liu <yuanhan.liu@...ux.intel.com>
To: mingo@...nel.org, hpa@...or.com, linux-kernel@...r.kernel.org,
peterz@...radead.org, bitbucket@...ine.de, tglx@...utronix.de
Cc: linux-tip-commits@...r.kernel.org, lkp@...org,
Fengguang Wu <fengguang.wu@...el.com>,
Huang Ying <ying.huang@...el.com>
Subject: Re: [tip:sched/core] sched, idle: Fix the idle polling state logic
On Wed, Sep 25, 2013 at 09:38:19AM -0700, tip-bot for Peter Zijlstra wrote:
> Commit-ID: ea8117478918a4734586d35ff530721b682425be
> Gitweb: http://git.kernel.org/tip/ea8117478918a4734586d35ff530721b682425be
> Author: Peter Zijlstra <peterz@...radead.org>
> AuthorDate: Wed, 11 Sep 2013 12:43:13 +0200
> Committer: Ingo Molnar <mingo@...nel.org>
> CommitDate: Wed, 25 Sep 2013 13:53:10 +0200
>
> sched, idle: Fix the idle polling state logic
>
> Mike reported that commit 7d1a9417 ("x86: Use generic idle loop")
> regressed several workloads and caused excessive reschedule
> interrupts.
Hi,
JFYI, this patch does reduce interruptes in our test:
platform: Sandbridge
testcase: aim7/creat-clo
* -- with this patch
O -- without this patch
interrupts.RES
1.2e+08 ++---------------------------------------------------------------+
| |
1e+08 O+ O O O O O O O O O O |
| |
| |
8e+07 ++ |
| |
6e+07 ++ |
| |
4e+07 ++ |
| |
| |
2e+07 ++ |
*....*....*....*....*....*.... ..*....*....*....*....*....*....*
0 ++----------------------------*----------------------------------+
vmstat.system.in
160000 ++----------------------------------------------------------------+
O O O |
140000 ++ O O O O O O O |
120000 ++ O |
| |
100000 ++ |
| |
80000 ++ |
| |
60000 ++ |
40000 ++ |
| |
20000 *+...*....*....*....*....*.... ..*....*....*....*....*....*
| *.....*.. |
0 ++----------------------------------------------------------------+
--yliu
>
> 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 tif_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>
> Cc: lenb@...nel.org
> Cc: tglx@...utronix.de
> Link: http://lkml.kernel.org/n/tip-nc03imb0etuefmzybzj7sprf@git.kernel.org
> Signed-off-by: Ingo Molnar <mingo@...nel.org>
> ---
> arch/x86/kernel/process.c | 6 ++--
> drivers/acpi/processor_idle.c | 46 ++++++-------------------
> drivers/idle/intel_idle.c | 2 +-
> include/linux/sched.h | 78 +++++++++++++++++++++++++++++++++++++++----
> include/linux/thread_info.h | 2 ++
> kernel/cpu/idle.c | 9 +++--
> 6 files changed, 91 insertions(+), 52 deletions(-)
>
> diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
> index c83516b..3fb8d95 100644
> --- 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();
> }
> diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
> index f98dd00..c7414a5 100644
> --- a/drivers/acpi/processor_idle.c
> +++ b/drivers/acpi/processor_idle.c
> @@ -119,17 +119,10 @@ static struct dmi_system_id processor_power_dmi_table[] = {
> */
> 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 (!tif_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 cpuidle_device *dev,
> 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 cpuidle_device *dev,
> 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 cpuidle_device *dev,
>
> 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 cpuidle_device *dev,
> }
> }
>
> - 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 cpuidle_device *dev,
>
> 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;
> }
> diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c
> index fa6964d..f116d66 100644
> --- a/drivers/idle/intel_idle.c
> +++ b/drivers/idle/intel_idle.c
> @@ -359,7 +359,7 @@ static int intel_idle(struct cpuidle_device *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();
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index b5344de..e783ec5 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -2479,34 +2479,98 @@ static inline int tsk_is_polling(struct task_struct *p)
> {
> 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(tif_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(tif_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(tif_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(tif_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(tif_need_resched());
> +}
> +static inline bool __must_check current_clr_polling_and_test(void)
> +{
> + return unlikely(tif_need_resched());
> +}
> #endif
>
> /*
> diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h
> index a629e4b..fddbe20 100644
> --- a/include/linux/thread_info.h
> +++ b/include/linux/thread_info.h
> @@ -118,6 +118,8 @@ static inline __deprecated void set_need_resched(void)
> */
> }
>
> +#define tif_need_resched() test_thread_flag(TIF_NEED_RESCHED)
> +
> #if defined TIF_RESTORE_SIGMASK && !defined HAVE_SET_RESTORE_SIGMASK
> /*
> * An arch can define its own version of set_restore_sigmask() to get the
> diff --git a/kernel/cpu/idle.c b/kernel/cpu/idle.c
> index e695c0a..c261409 100644
> --- 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 (!tif_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();
> }
> @@ -129,7 +128,7 @@ void cpu_startup_entry(enum cpuhp_state state)
> */
> boot_init_stack_canary();
> #endif
> - current_set_polling();
> + __current_set_polling();
> arch_cpu_idle_prepare();
> cpu_idle_loop();
> }
> --
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