arch/x86/kernel/process.c

   1 #include <linux/errno.h>
   2 #include <linux/kernel.h>
   3 #include <linux/mm.h>
   4 #include <linux/smp.h>
   5 #include <linux/slab.h>
   6 #include <linux/sched.h>
   7 #include <linux/module.h>
   8 #include <linux/pm.h>
   9
  10 struct kmem_cache *task_xstate_cachep;
  11
  12 int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
  13 {
  14         *dst = *src;
  15         if (src->thread.xstate) {
  16                 dst->thread.xstate = kmem_cache_alloc(task_xstate_cachep,
  17                                                       GFP_KERNEL);
  18                 if (!dst->thread.xstate)
  19                         return -ENOMEM;
  20                 WARN_ON((unsigned long)dst->thread.xstate & 15);
  21                 memcpy(dst->thread.xstate, src->thread.xstate, xstate_size);
  22         }
  23         return 0;
  24 }
  25
  26 void free_thread_xstate(struct task_struct *tsk)
  27 {
  28         if (tsk->thread.xstate) {
  29                 kmem_cache_free(task_xstate_cachep, tsk->thread.xstate);
  30                 tsk->thread.xstate = NULL;
  31         }
  32 }
  33
  34 void free_thread_info(struct thread_info *ti)
  35 {
  36         free_thread_xstate(ti->task);
  37         free_pages((unsigned long)ti, get_order(THREAD_SIZE));
  38 }
  39
  40 void arch_task_cache_init(void)
  41 {
  42         task_xstate_cachep =
  43                 kmem_cache_create("task_xstate", xstate_size,
  44                                   __alignof__(union thread_xstate),
  45                                   SLAB_PANIC, NULL);
  46 }
  47
  48 static void do_nothing(void *unused)
  49 {
  50 }
  51
  52 /*
  53  * cpu_idle_wait - Used to ensure that all the CPUs discard old value of
  54  * pm_idle and update to new pm_idle value. Required while changing pm_idle
  55  * handler on SMP systems.
  56  *
  57  * Caller must have changed pm_idle to the new value before the call. Old
  58  * pm_idle value will not be used by any CPU after the return of this function.
  59  */
  60 void cpu_idle_wait(void)
  61 {
  62         smp_mb();
  63         /* kick all the CPUs so that they exit out of pm_idle */
  64         smp_call_function(do_nothing, NULL, 0, 1);
  65 }
  66 EXPORT_SYMBOL_GPL(cpu_idle_wait);
  67
  68 /*
  69  * This uses new MONITOR/MWAIT instructions on P4 processors with PNI,
  70  * which can obviate IPI to trigger checking of need_resched.
  71  * We execute MONITOR against need_resched and enter optimized wait state
  72  * through MWAIT. Whenever someone changes need_resched, we would be woken
  73  * up from MWAIT (without an IPI).
  74  *
  75  * New with Core Duo processors, MWAIT can take some hints based on CPU
  76  * capability.
  77  */
  78 void mwait_idle_with_hints(unsigned long ax, unsigned long cx)
  79 {
  80         if (!need_resched()) {
  81                 __monitor((void *)&current_thread_info()->flags, 0, 0);
  82                 smp_mb();
  83                 if (!need_resched())
  84                         __mwait(ax, cx);
  85         }
  86 }
  87
  88 /* Default MONITOR/MWAIT with no hints, used for default C1 state */
  89 static void mwait_idle(void)
  90 {
  91         if (!need_resched()) {
  92                 __monitor((void *)&current_thread_info()->flags, 0, 0);
  93                 smp_mb();
  94                 if (!need_resched())
  95                         __sti_mwait(0, 0);
  96                 else
  97                         local_irq_enable();
  98         } else
  99                 local_irq_enable();
 100 }
 101
 102
 103 static int __cpuinit mwait_usable(const struct cpuinfo_x86 *c)
 104 {
 105         if (force_mwait)
 106                 return 1;
 107         /* Any C1 states supported? */
 108         return c->cpuid_level >= 5 && ((cpuid_edx(5) >> 4) & 0xf) > 0;
 109 }
 110
 111 /*
 112  * On SMP it's slightly faster (but much more power-consuming!)
 113  * to poll the ->work.need_resched flag instead of waiting for the
 114  * cross-CPU IPI to arrive. Use this option with caution.
 115  */
 116 static void poll_idle(void)
 117 {
 118         local_irq_enable();
 119         cpu_relax();
 120 }
 121
 122 void __cpuinit select_idle_routine(const struct cpuinfo_x86 *c)
 123 {
 124         static int selected;
 125
 126         if (selected)
 127                 return;
 128 #ifdef CONFIG_X86_SMP
 129         if (pm_idle == poll_idle && smp_num_siblings > 1) {
 130                 printk(KERN_WARNING "WARNING: polling idle and HT enabled,"
 131                         " performance may degrade.\n");
 132         }
 133 #endif
 134         if (cpu_has(c, X86_FEATURE_MWAIT) && mwait_usable(c)) {
 135                 /*
 136                  * Skip, if setup has overridden idle.
 137                  * One CPU supports mwait => All CPUs supports mwait
 138                  */
 139                 if (!pm_idle) {
 140                         printk(KERN_INFO "using mwait in idle threads.\n");
 141                         pm_idle = mwait_idle;
 142                 }
 143         }
 144         selected = 1;
 145 }
 146
 147 static int __init idle_setup(char *str)
 148 {
 149         if (!strcmp(str, "poll")) {
 150                 printk("using polling idle threads.\n");
 151                 pm_idle = poll_idle;
 152         } else if (!strcmp(str, "mwait"))
 153                 force_mwait = 1;
 154         else
 155                 return -1;
 156
 157         boot_option_idle_override = 1;
 158         return 0;
 159 }
 160 early_param("idle", idle_setup);
 161