Hi Peter,
3.12 escaped without this regression being fixed, nor does the fix have
a stable tag. Suspecting it may have just fallen through a crack...
core2 boxen still have post mwait_idle() removal regressions (rainy day
job, started digging, rain went missing), but more modern westmere box
likes this fix quite a lot.
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date: Wed, 11 Sep 2013 12:43:13 +0200
Subject: sched, idle: Fix the idle polling state logic
Commit ea8117478918a4734586d35ff530721b682425be upstream
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).
(Mike: dropped need_resched() -> tif_need_resched() for @stable)
Reported-by: Mike Galbraith <bitbucket@xxxxxxxxx>
Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: lenb@xxxxxxxxxx
Cc: tglx@xxxxxxxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx # 3.10+
Link: http://lkml.kernel.org/n/tip-nc03imb0etuefmzybzj7sprf@xxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
arch/x86/kernel/process.c | 6 +--
drivers/acpi/processor_idle.c | 44 ++++-------------------
drivers/idle/intel_idle.c | 2 -
include/linux/sched.h | 78 ++++++++++++++++++++++++++++++++++++++----
kernel/cpu/idle.c | 7 +--
5 files changed, 87 insertions(+), 50 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()) {
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
@@ -2479,34 +2479,98 @@ 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(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(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(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(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(need_resched());
+}
+static inline bool __must_check current_clr_polling_and_test(void)
+{
+ return unlikely(need_resched());
+}
#endif
/*
--- a/kernel/cpu/idle.c
+++ b/kernel/cpu/idle.c
@@ -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
*/
boot_init_stack_canary();
#endif
- current_set_polling();
+ __current_set_polling();
arch_cpu_idle_prepare();
cpu_idle_loop();
}
--
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