diff options
Diffstat (limited to 'arch/x86/kernel/process.c')
| -rw-r--r-- | arch/x86/kernel/process.c | 117 |
1 files changed, 117 insertions, 0 deletions
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c index 3004d716539d..67e9b4a1e89d 100644 --- a/arch/x86/kernel/process.c +++ b/arch/x86/kernel/process.c @@ -4,6 +4,8 @@ #include <linux/smp.h> #include <linux/slab.h> #include <linux/sched.h> +#include <linux/module.h> +#include <linux/pm.h> struct kmem_cache *task_xstate_cachep; @@ -42,3 +44,118 @@ void arch_task_cache_init(void) __alignof__(union thread_xstate), SLAB_PANIC, NULL); } + +static void do_nothing(void *unused) +{ +} + +/* + * cpu_idle_wait - Used to ensure that all the CPUs discard old value of + * pm_idle and update to new pm_idle value. Required while changing pm_idle + * handler on SMP systems. + * + * Caller must have changed pm_idle to the new value before the call. Old + * pm_idle value will not be used by any CPU after the return of this function. + */ +void cpu_idle_wait(void) +{ + smp_mb(); + /* kick all the CPUs so that they exit out of pm_idle */ + smp_call_function(do_nothing, NULL, 0, 1); +} +EXPORT_SYMBOL_GPL(cpu_idle_wait); + +/* + * This uses new MONITOR/MWAIT instructions on P4 processors with PNI, + * which can obviate IPI to trigger checking of need_resched. + * We execute MONITOR against need_resched and enter optimized wait state + * through MWAIT. Whenever someone changes need_resched, we would be woken + * up from MWAIT (without an IPI). + * + * New with Core Duo processors, MWAIT can take some hints based on CPU + * capability. + */ +void mwait_idle_with_hints(unsigned long ax, unsigned long cx) +{ + if (!need_resched()) { + __monitor((void *)¤t_thread_info()->flags, 0, 0); + smp_mb(); + if (!need_resched()) + __mwait(ax, cx); + } +} + +/* Default MONITOR/MWAIT with no hints, used for default C1 state */ +static void mwait_idle(void) +{ + if (!need_resched()) { + __monitor((void *)¤t_thread_info()->flags, 0, 0); + smp_mb(); + if (!need_resched()) + __sti_mwait(0, 0); + else + local_irq_enable(); + } else + local_irq_enable(); +} + + +static int __cpuinit mwait_usable(const struct cpuinfo_x86 *c) +{ + if (force_mwait) + return 1; + /* Any C1 states supported? */ + return c->cpuid_level >= 5 && ((cpuid_edx(5) >> 4) & 0xf) > 0; +} + +/* + * On SMP it's slightly faster (but much more power-consuming!) + * to poll the ->work.need_resched flag instead of waiting for the + * cross-CPU IPI to arrive. Use this option with caution. + */ +static void poll_idle(void) +{ + local_irq_enable(); + cpu_relax(); +} + +void __cpuinit select_idle_routine(const struct cpuinfo_x86 *c) +{ + static int selected; + + if (selected) + return; +#ifdef CONFIG_X86_SMP + if (pm_idle == poll_idle && smp_num_siblings > 1) { + printk(KERN_WARNING "WARNING: polling idle and HT enabled," + " performance may degrade.\n"); + } +#endif + if (cpu_has(c, X86_FEATURE_MWAIT) && mwait_usable(c)) { + /* + * Skip, if setup has overridden idle. + * One CPU supports mwait => All CPUs supports mwait + */ + if (!pm_idle) { + printk(KERN_INFO "using mwait in idle threads.\n"); + pm_idle = mwait_idle; + } + } + selected = 1; +} + +static int __init idle_setup(char *str) +{ + if (!strcmp(str, "poll")) { + printk("using polling idle threads.\n"); + pm_idle = poll_idle; + } else if (!strcmp(str, "mwait")) + force_mwait = 1; + else + return -1; + + boot_option_idle_override = 1; + return 0; +} +early_param("idle", idle_setup); + |