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  * On SMP it's slightly faster (but much more power-consuming!)
 104  * to poll the ->work.need_resched flag instead of waiting for the
 105  * cross-CPU IPI to arrive. Use this option with caution.
 106  */
 107 static void poll_idle(void)
 108 {
 109         local_irq_enable();
 110         cpu_relax();
 111 }
 112
 113 /*
 114  * mwait selection logic:
 115  *
 116  * It depends on the CPU. For AMD CPUs that support MWAIT this is
 117  * wrong. Family 0x10 and 0x11 CPUs will enter C1 on HLT. Powersavings
 118  * then depend on a clock divisor and current Pstate of the core. If
 119  * all cores of a processor are in halt state (C1) the processor can
 120  * enter the C1E (C1 enhanced) state. If mwait is used this will never
 121  * happen.
 122  *
 123  * idle=mwait overrides this decision and forces the usage of mwait.
 124  */
 125 static int __cpuinit mwait_usable(const struct cpuinfo_x86 *c)
 126 {
 127         if (force_mwait)
 128                 return 1;
 129
 130         if (c->x86_vendor == X86_VENDOR_AMD) {
 131                 switch(c->x86) {
 132                 case 0x10:
 133                 case 0x11:
 134                         return 0;
 135                 }
 136         }
 137         return 1;
 138 }
 139
 140 void __cpuinit select_idle_routine(const struct cpuinfo_x86 *c)
 141 {
 142         static int selected;
 143
 144         if (selected)
 145                 return;
 146 #ifdef CONFIG_X86_SMP
 147         if (pm_idle == poll_idle && smp_num_siblings > 1) {
 148                 printk(KERN_WARNING "WARNING: polling idle and HT enabled,"
 149                         " performance may degrade.\n");
 150         }
 151 #endif
 152         if (cpu_has(c, X86_FEATURE_MWAIT) && mwait_usable(c)) {
 153                 /*
 154                  * Skip, if setup has overridden idle.
 155                  * One CPU supports mwait => All CPUs supports mwait
 156                  */
 157                 if (!pm_idle) {
 158                         printk(KERN_INFO "using mwait in idle threads.\n");
 159                         pm_idle = mwait_idle;
 160                 }
 161         }
 162         selected = 1;
 163 }
 164
 165 static int __init idle_setup(char *str)
 166 {
 167         if (!strcmp(str, "poll")) {
 168                 printk("using polling idle threads.\n");
 169                 pm_idle = poll_idle;
 170         } else if (!strcmp(str, "mwait"))
 171                 force_mwait = 1;
 172         else
 173                 return -1;
 174
 175         boot_option_idle_override = 1;
 176         return 0;
 177 }
 178 early_param("idle", idle_setup);
 179