nohz: prevent tick stop outside of the idle loop
[linux-2.6.git] / arch / powerpc / kernel / idle.c
1 /*
2  * Idle daemon for PowerPC.  Idle daemon will handle any action
3  * that needs to be taken when the system becomes idle.
4  *
5  * Originally written by Cort Dougan (cort@cs.nmt.edu).
6  * Subsequent 32-bit hacking by Tom Rini, Armin Kuster,
7  * Paul Mackerras and others.
8  *
9  * iSeries supported added by Mike Corrigan <mikejc@us.ibm.com>
10  *
11  * Additional shared processor, SMT, and firmware support
12  *    Copyright (c) 2003 Dave Engebretsen <engebret@us.ibm.com>
13  *
14  * 32-bit and 64-bit versions merged by Paul Mackerras <paulus@samba.org>
15  *
16  * This program is free software; you can redistribute it and/or
17  * modify it under the terms of the GNU General Public License
18  * as published by the Free Software Foundation; either version
19  * 2 of the License, or (at your option) any later version.
20  */
21
22 #include <linux/sched.h>
23 #include <linux/kernel.h>
24 #include <linux/smp.h>
25 #include <linux/cpu.h>
26 #include <linux/sysctl.h>
27 #include <linux/tick.h>
28
29 #include <asm/system.h>
30 #include <asm/processor.h>
31 #include <asm/cputable.h>
32 #include <asm/time.h>
33 #include <asm/machdep.h>
34 #include <asm/smp.h>
35
36 #ifdef CONFIG_HOTPLUG_CPU
37 /* this is used for software suspend, and that shuts down
38  * CPUs even while the system is still booting... */
39 #define cpu_should_die()        (cpu_is_offline(smp_processor_id()) && \
40                                    (system_state == SYSTEM_RUNNING     \
41                                  || system_state == SYSTEM_BOOTING))
42 #else
43 #define cpu_should_die()        0
44 #endif
45
46 static int __init powersave_off(char *arg)
47 {
48         ppc_md.power_save = NULL;
49         return 0;
50 }
51 __setup("powersave=off", powersave_off);
52
53 /*
54  * The body of the idle task.
55  */
56 void cpu_idle(void)
57 {
58         if (ppc_md.idle_loop)
59                 ppc_md.idle_loop();     /* doesn't return */
60
61         set_thread_flag(TIF_POLLING_NRFLAG);
62         while (1) {
63                 tick_nohz_stop_sched_tick(1);
64                 while (!need_resched() && !cpu_should_die()) {
65                         ppc64_runlatch_off();
66
67                         if (ppc_md.power_save) {
68                                 clear_thread_flag(TIF_POLLING_NRFLAG);
69                                 /*
70                                  * smp_mb is so clearing of TIF_POLLING_NRFLAG
71                                  * is ordered w.r.t. need_resched() test.
72                                  */
73                                 smp_mb();
74                                 local_irq_disable();
75
76                                 /* check again after disabling irqs */
77                                 if (!need_resched() && !cpu_should_die())
78                                         ppc_md.power_save();
79
80                                 local_irq_enable();
81                                 set_thread_flag(TIF_POLLING_NRFLAG);
82
83                         } else {
84                                 /*
85                                  * Go into low thread priority and possibly
86                                  * low power mode.
87                                  */
88                                 HMT_low();
89                                 HMT_very_low();
90                         }
91                 }
92
93                 HMT_medium();
94                 ppc64_runlatch_on();
95                 tick_nohz_restart_sched_tick();
96                 if (cpu_should_die())
97                         cpu_die();
98                 preempt_enable_no_resched();
99                 schedule();
100                 preempt_disable();
101         }
102 }
103
104 int powersave_nap;
105
106 #ifdef CONFIG_SYSCTL
107 /*
108  * Register the sysctl to set/clear powersave_nap.
109  */
110 static ctl_table powersave_nap_ctl_table[]={
111         {
112                 .ctl_name       = KERN_PPC_POWERSAVE_NAP,
113                 .procname       = "powersave-nap",
114                 .data           = &powersave_nap,
115                 .maxlen         = sizeof(int),
116                 .mode           = 0644,
117                 .proc_handler   = &proc_dointvec,
118         },
119         {}
120 };
121 static ctl_table powersave_nap_sysctl_root[] = {
122         {
123                 .ctl_name       = CTL_KERN,
124                 .procname       = "kernel",
125                 .mode           = 0555,
126                 .child          = powersave_nap_ctl_table,
127         },
128         {}
129 };
130
131 static int __init
132 register_powersave_nap_sysctl(void)
133 {
134         register_sysctl_table(powersave_nap_sysctl_root);
135
136         return 0;
137 }
138 __initcall(register_powersave_nap_sysctl);
139 #endif