Re: [patch 08/34] arm: Use generic idle loop

From: Thomas Gleixner
Date: Tue Apr 09 2013 - 05:20:52 EST

Russell,

On Mon, 8 Apr 2013, Russell King - ARM Linux wrote:
> On Mon, Mar 25, 2013 at 03:02:39PM +0100, Thomas Gleixner wrote:
> So, how can I review these changes when all there is is a git URL, and
> I *do* not want to pull them into my tree without first looking at the
> patches, possibly reviewing them and *replying* with the patch inline?

the patches were CC'ed to LKML and linux-arch and I expected that you
are at least having the latter. Find the relevant patch inlined below.

> I see you've now added this stuff to -tip. I guess ARM doesn't matter
> to you at all. I guess having ARM people review the core changes doesn't
> matter either.
>
> Well, I guess if it's broken, we'll just have to fix it up after the
> merge window.
>
> One rule for x86, a different one for ARM. Let x86 maintainers moan
> about ARM people, but don't let ARM people moan about x86 maintainers.
> Yes, sure, right, I get it.

Sigh no.

> So, explicitly, my concern is this replacement of enable_hlt()/disable_hlt()
> with this cpu_idle_poll_ctrl(), and whether this interface is still
> counted - so that it's possible to call disable_hlt() to _permanently_
> disable any hlt-based idle loop.

It is a counter. I looked carefully at all the various slightly
differently fcked up implementations and picked the counter based one
as it fits all requirements.

Thanks,

tglx
---
Subject: idle: Implement generic idle function
From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Date: Thu, 21 Mar 2013 22:49:35 +0100

All idle functions in arch/* are more or less the same, plus minus a
few bugs and extra instrumentation, tickless support and other
optional items.

Implement a generic idle function which resembles the functionality
found in arch/. Provide weak arch_cpu_idle_* functions which can be
overridden by the architecture code if needed.

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Cc: Paul McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Reviewed-by: Cc: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx>
Cc: Magnus Damm <magnus.damm@xxxxxxxxx>
Link: http://lkml.kernel.org/r/20130321215233.646635455@xxxxxxxxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
arch/Kconfig | 3 +
include/linux/cpu.h | 8 +++
kernel/cpu/idle.c | 105 ++++++++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 116 insertions(+)

Index: linux-2.6/arch/Kconfig
===================================================================
--- linux-2.6.orig/arch/Kconfig
+++ linux-2.6/arch/Kconfig
@@ -216,6 +216,9 @@ config USE_GENERIC_SMP_HELPERS
config GENERIC_SMP_IDLE_THREAD
bool

+config GENERIC_IDLE_LOOP
+ bool
+
# Select if arch init_task initializer is different to init/init_task.c
config ARCH_INIT_TASK
bool
Index: linux-2.6/include/linux/cpu.h
===================================================================
--- linux-2.6.orig/include/linux/cpu.h
+++ linux-2.6/include/linux/cpu.h
@@ -220,4 +220,12 @@ enum cpuhp_state {
void cpu_startup_entry(enum cpuhp_state state);
void cpu_idle(void);

+void cpu_idle_poll_ctrl(bool enable);
+
+void arch_cpu_idle(void);
+void arch_cpu_idle_prepare(void);
+void arch_cpu_idle_enter(void);
+void arch_cpu_idle_exit(void);
+void arch_cpu_idle_dead(void);
+
#endif /* _LINUX_CPU_H_ */
Index: linux-2.6/kernel/cpu/idle.c
===================================================================
--- linux-2.6.orig/kernel/cpu/idle.c
+++ linux-2.6/kernel/cpu/idle.c
@@ -3,8 +3,113 @@
*/
#include <linux/sched.h>
#include <linux/cpu.h>
+#include <linux/tick.h>
+#include <linux/mm.h>

+#include <asm/tlb.h>
+
+#include <trace/events/power.h>
+
+#ifndef CONFIG_GENERIC_IDLE_LOOP
void cpu_startup_entry(enum cpuhp_state state)
{
cpu_idle();
}
+#else
+
+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)
+{
+ trace_cpu_idle_rcuidle(0, smp_processor_id());
+ local_irq_enable();
+ while (!need_resched())
+ cpu_relax();
+ trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, smp_processor_id());
+ 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;
+}
+
+/*
+ * 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();
+
+ if (cpu_idle_force_poll) {
+ cpu_idle_poll();
+ } else {
+ current_clr_polling();
+ if (!need_resched()) {
+ stop_critical_timings();
+ rcu_idle_enter();
+ arch_cpu_idle();
+ WARN_ON_ONCE(irqs_disabled());
+ rcu_idle_exit();
+ start_critical_timings();
+ } else {
+ local_irq_enable();
+ }
+ current_set_polling();
+ }
+ arch_cpu_idle_exit();
+ }
+ tick_nohz_idle_exit();
+ schedule_preempt_disabled();
+ }
+}
+
+void cpu_startup_entry(enum cpuhp_state state)
+{
+ current_set_polling();
+ arch_cpu_idle_prepare();
+ cpu_idle_loop();
+}
+#endif
--
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