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Message-ID: <20140224172207.GC9987@twins.programming.kicks-ass.net>
Date: Mon, 24 Feb 2014 18:22:07 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Daniel Lezcano <daniel.lezcano@...aro.org>
Cc: mingo@...nel.org, tglx@...utronix.de, rjw@...ysocki.net,
nicolas.pitre@...aro.org, preeti@...ux.vnet.ibm.com,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2 4/5] idle: Move idle conditions in cpuidle_idle main
function
On Mon, Feb 24, 2014 at 06:03:10PM +0100, Daniel Lezcano wrote:
> Well there is the polling idle state for the x86 and ppc cpuidle drivers.
> Except that, I think we have something more or less clean.
Yeah, they have to set it back to polling again :/
Ideally we'd sweep the entire tree and switch the default polling state
to polling and add a current_clr_polling_and_test() to all WFI/HLT like
ones that need the interrupt.
But lots of work that.
> >- if (need_resched()) {
>
> Ok. The need_resched is now replaced by 'current_clr_polling_and_test', with
> a call to '__current_set_polling()' to set the flag back, right ?
Yah.
> For my personal information, what is the subtlety with:
>
> if (tif_need_resched())
> set_preempt_need_resched();
>
> ?
Urgh, looks like something went wrong with: cf37b6b48428d
That commit doesn't actually remove kernel/cpu/idle.c nor is the new
code an exact replica of the old one.
Ingo, any chance we can get that fixed?
Daniel; does the below change/comment clarify?
---
Subject: sched/idle: Fixup merge fail of idle.c move
Commit cf37b6b48428d ("sched/idle: Move cpu/idle.c to sched/idle.c")
said to simply move a file; somehow it got mangled and created an old
version of the file and forgot to remove the old file.
Fix this fail; add the lost change and remove the now identical old
file.
Cc: Nicolas Pitre <nico@...aro.org>
Fixes: cf37b6b48428d ("sched/idle: Move cpu/idle.c to sched/idle.c")
Signed-off-by: Peter Zijlstra <peterz@...radead.org>
---
kernel/cpu/idle.c | 147 ----------------------------------------------------
kernel/sched/idle.c | 17 +++---
2 files changed, 10 insertions(+), 154 deletions(-)
diff --git a/kernel/cpu/idle.c b/kernel/cpu/idle.c
deleted file mode 100644
index b7976a127178..000000000000
--- a/kernel/cpu/idle.c
+++ /dev/null
@@ -1,147 +0,0 @@
-/*
- * Generic entry point for the idle threads
- */
-#include <linux/sched.h>
-#include <linux/cpu.h>
-#include <linux/cpuidle.h>
-#include <linux/tick.h>
-#include <linux/mm.h>
-#include <linux/stackprotector.h>
-
-#include <asm/tlb.h>
-
-#include <trace/events/power.h>
-
-static int __read_mostly cpu_idle_force_poll;
-
-void cpu_idle_poll_ctrl(bool enable)
-{
- if (enable) {
- cpu_idle_force_poll++;
- } else {
- cpu_idle_force_poll--;
- WARN_ON_ONCE(cpu_idle_force_poll < 0);
- }
-}
-
-#ifdef CONFIG_GENERIC_IDLE_POLL_SETUP
-static int __init cpu_idle_poll_setup(char *__unused)
-{
- cpu_idle_force_poll = 1;
- return 1;
-}
-__setup("nohlt", cpu_idle_poll_setup);
-
-static int __init cpu_idle_nopoll_setup(char *__unused)
-{
- cpu_idle_force_poll = 0;
- return 1;
-}
-__setup("hlt", cpu_idle_nopoll_setup);
-#endif
-
-static inline int cpu_idle_poll(void)
-{
- rcu_idle_enter();
- trace_cpu_idle_rcuidle(0, smp_processor_id());
- local_irq_enable();
- while (!tif_need_resched())
- cpu_relax();
- trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, smp_processor_id());
- rcu_idle_exit();
- return 1;
-}
-
-/* Weak implementations for optional arch specific functions */
-void __weak arch_cpu_idle_prepare(void) { }
-void __weak arch_cpu_idle_enter(void) { }
-void __weak arch_cpu_idle_exit(void) { }
-void __weak arch_cpu_idle_dead(void) { }
-void __weak arch_cpu_idle(void)
-{
- cpu_idle_force_poll = 1;
- local_irq_enable();
-}
-
-/*
- * Generic idle loop implementation
- */
-static void cpu_idle_loop(void)
-{
- while (1) {
- tick_nohz_idle_enter();
-
- while (!need_resched()) {
- check_pgt_cache();
- rmb();
-
- if (cpu_is_offline(smp_processor_id()))
- arch_cpu_idle_dead();
-
- local_irq_disable();
- arch_cpu_idle_enter();
-
- /*
- * In poll mode we reenable interrupts and spin.
- *
- * Also if we detected in the wakeup from idle
- * path that the tick broadcast device expired
- * for us, we don't want to go deep idle as we
- * know that the IPI is going to arrive right
- * away
- */
- if (cpu_idle_force_poll || tick_check_broadcast_expired()) {
- cpu_idle_poll();
- } else {
- if (!current_clr_polling_and_test()) {
- stop_critical_timings();
- rcu_idle_enter();
- if (cpuidle_idle_call())
- arch_cpu_idle();
- if (WARN_ON_ONCE(irqs_disabled()))
- local_irq_enable();
- rcu_idle_exit();
- start_critical_timings();
- } else {
- local_irq_enable();
- }
- __current_set_polling();
- }
- arch_cpu_idle_exit();
- }
-
- /*
- * Since we fell out of the loop above, we know
- * TIF_NEED_RESCHED must be set, propagate it into
- * PREEMPT_NEED_RESCHED.
- *
- * This is required because for polling idle loops we will
- * not have had an IPI to fold the state for us.
- */
- preempt_set_need_resched();
- tick_nohz_idle_exit();
- schedule_preempt_disabled();
- }
-}
-
-void cpu_startup_entry(enum cpuhp_state state)
-{
- /*
- * This #ifdef needs to die, but it's too late in the cycle to
- * make this generic (arm and sh have never invoked the canary
- * init for the non boot cpus!). Will be fixed in 3.11
- */
-#ifdef CONFIG_X86
- /*
- * If we're the non-boot CPU, nothing set the stack canary up
- * for us. The boot CPU already has it initialized but no harm
- * in doing it again. This is a good place for updating it, as
- * we wont ever return from this function (so the invalid
- * canaries already on the stack wont ever trigger).
- */
- boot_init_stack_canary();
-#endif
- __current_set_polling();
- arch_cpu_idle_prepare();
- cpu_idle_loop();
-}
diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index 14ca43430aee..b7976a127178 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -108,14 +108,17 @@ static void cpu_idle_loop(void)
__current_set_polling();
}
arch_cpu_idle_exit();
- /*
- * We need to test and propagate the TIF_NEED_RESCHED
- * bit here because we might not have send the
- * reschedule IPI to idle tasks.
- */
- if (tif_need_resched())
- set_preempt_need_resched();
}
+
+ /*
+ * Since we fell out of the loop above, we know
+ * TIF_NEED_RESCHED must be set, propagate it into
+ * PREEMPT_NEED_RESCHED.
+ *
+ * This is required because for polling idle loops we will
+ * not have had an IPI to fold the state for us.
+ */
+ preempt_set_need_resched();
tick_nohz_idle_exit();
schedule_preempt_disabled();
}
--
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