ACPI: acpi_idle: touch TS_POLLING only in the non-MWAIT case

commit d306ebc28649b89877a22158fe0076f06cc46f60
(ACPI: Be in TS_POLLING state during mwait based C-state entry)
fixed an important power & performance issue where ACPI c2 and c3 C-states
were clearing TS_POLLING even when using MWAIT (ACPI_STATE_FFH).
That bug had been causing us to receive redundant scheduling interrups
when we had already been woken up by MONITOR/MWAIT.

Following up on that...

In the MWAIT case, we don't have to subsequently
check need_resched(), as that c heck was there
for the TS_POLLING-clearing case.

Note that not only does the cpuidle calling function
already check need_resched() before calling us, the
low-level entry into monitor/mwait calls it twice --
guaranteeing that a write to the trigger address
can not go un-noticed.

Also, in this case, we don't have to set TS_POLLING
when we wake, because we never cleared it.

Signed-off-by: Len Brown <[e-mail]>
Acked-by: Venkatesh Pallipadi <[e-mail]>

drivers/acpi/processor_idle.c

···
 		return(acpi_idle_enter_c1(dev, state));
 
 	local_irq_disable();
+
 	if (cx->entry_method != ACPI_CSTATE_FFH) {
 		current_thread_info()->status &= ~TS_POLLING;
 		/*
···
 		 * NEED_RESCHED:
 		 */
 		smp_mb();
-	}
 
-	if (unlikely(need_resched())) {
-		current_thread_info()->status |= TS_POLLING;
-		local_irq_enable();
-		return 0;
+		if (unlikely(need_resched())) {
+			current_thread_info()->status |= TS_POLLING;
+			local_irq_enable();
+			return 0;
+		}
 	}
 
 	/*
···
 	sched_clock_idle_wakeup_event(sleep_ticks*PM_TIMER_TICK_NS);
 
 	local_irq_enable();
-	current_thread_info()->status |= TS_POLLING;
+	if (cx->entry_method != ACPI_CSTATE_FFH)
+		current_thread_info()->status |= TS_POLLING;
 
 	cx->usage++;
 
···
 	}
 
 	local_irq_disable();
+
 	if (cx->entry_method != ACPI_CSTATE_FFH) {
 		current_thread_info()->status &= ~TS_POLLING;
 		/*
···
 		 * NEED_RESCHED:
 		 */
 		smp_mb();
-	}
 
-	if (unlikely(need_resched())) {
-		current_thread_info()->status |= TS_POLLING;
-		local_irq_enable();
-		return 0;
+		if (unlikely(need_resched())) {
+			current_thread_info()->status |= TS_POLLING;
+			local_irq_enable();
+			return 0;
+		}
 	}
 
 	acpi_unlazy_tlb(smp_processor_id());
···
 	sched_clock_idle_wakeup_event(sleep_ticks*PM_TIMER_TICK_NS);
 
 	local_irq_enable();
-	current_thread_info()->status |= TS_POLLING;
+	if (cx->entry_method != ACPI_CSTATE_FFH)
+		current_thread_info()->status |= TS_POLLING;
 
 	cx->usage++;