diff options
| -rw-r--r-- | drivers/acpi/processor_idle.c | 38 | ||||
| -rw-r--r-- | drivers/net/wireless/ipw2100.c | 10 | ||||
| -rw-r--r-- | include/linux/latency.h | 25 | ||||
| -rw-r--r-- | kernel/Makefile | 2 | ||||
| -rw-r--r-- | kernel/latency.c | 279 |
5 files changed, 349 insertions, 5 deletions
diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c index 71066066d626b..0a395fca843b4 100644 --- a/drivers/acpi/processor_idle.c +++ b/drivers/acpi/processor_idle.c @@ -38,6 +38,7 @@ #include <linux/dmi.h> #include <linux/moduleparam.h> #include <linux/sched.h> /* need_resched() */ +#include <linux/latency.h> #include <asm/io.h> #include <asm/uaccess.h> @@ -453,7 +454,8 @@ static void acpi_processor_idle(void) */ if (cx->promotion.state && ((cx->promotion.state - pr->power.states) <= max_cstate)) { - if (sleep_ticks > cx->promotion.threshold.ticks) { + if (sleep_ticks > cx->promotion.threshold.ticks && + cx->promotion.state->latency <= system_latency_constraint()) { cx->promotion.count++; cx->demotion.count = 0; if (cx->promotion.count >= @@ -494,8 +496,10 @@ static void acpi_processor_idle(void) end: /* * Demote if current state exceeds max_cstate + * or if the latency of the current state is unacceptable */ - if ((pr->power.state - pr->power.states) > max_cstate) { + if ((pr->power.state - pr->power.states) > max_cstate || + pr->power.state->latency > system_latency_constraint()) { if (cx->demotion.state) next_state = cx->demotion.state; } @@ -1009,9 +1013,11 @@ static int acpi_processor_power_seq_show(struct seq_file *seq, void *offset) seq_printf(seq, "active state: C%zd\n" "max_cstate: C%d\n" - "bus master activity: %08x\n", + "bus master activity: %08x\n" + "maximum allowed latency: %d usec\n", pr->power.state ? pr->power.state - pr->power.states : 0, - max_cstate, (unsigned)pr->power.bm_activity); + max_cstate, (unsigned)pr->power.bm_activity, + system_latency_constraint()); seq_puts(seq, "states:\n"); @@ -1077,6 +1083,28 @@ static const struct file_operations acpi_processor_power_fops = { .release = single_release, }; +static void smp_callback(void *v) +{ + /* we already woke the CPU up, nothing more to do */ +} + +/* + * This function gets called when a part of the kernel has a new latency + * requirement. This means we need to get all processors out of their C-state, + * and then recalculate a new suitable C-state. Just do a cross-cpu IPI; that + * wakes them all right up. + */ +static int acpi_processor_latency_notify(struct notifier_block *b, + unsigned long l, void *v) +{ + smp_call_function(smp_callback, NULL, 0, 1); + return NOTIFY_OK; +} + +static struct notifier_block acpi_processor_latency_notifier = { + .notifier_call = acpi_processor_latency_notify, +}; + int acpi_processor_power_init(struct acpi_processor *pr, struct acpi_device *device) { @@ -1093,6 +1121,7 @@ int acpi_processor_power_init(struct acpi_processor *pr, "ACPI: processor limited to max C-state %d\n", max_cstate); first_run++; + register_latency_notifier(&acpi_processor_latency_notifier); } if (!pr) @@ -1164,6 +1193,7 @@ int acpi_processor_power_exit(struct acpi_processor *pr, * copies of pm_idle before proceeding. */ cpu_idle_wait(); + unregister_latency_notifier(&acpi_processor_latency_notifier); } return 0; diff --git a/drivers/net/wireless/ipw2100.c b/drivers/net/wireless/ipw2100.c index 6c5add701a6fc..97937809de095 100644 --- a/drivers/net/wireless/ipw2100.c +++ b/drivers/net/wireless/ipw2100.c @@ -163,6 +163,7 @@ that only one external action is invoked at a time. #include <linux/firmware.h> #include <linux/acpi.h> #include <linux/ctype.h> +#include <linux/latency.h> #include "ipw2100.h" @@ -1697,6 +1698,11 @@ static int ipw2100_up(struct ipw2100_priv *priv, int deferred) return 0; } + /* the ipw2100 hardware really doesn't want power management delays + * longer than 175usec + */ + modify_acceptable_latency("ipw2100", 175); + /* If the interrupt is enabled, turn it off... */ spin_lock_irqsave(&priv->low_lock, flags); ipw2100_disable_interrupts(priv); @@ -1849,6 +1855,8 @@ static void ipw2100_down(struct ipw2100_priv *priv) ipw2100_disable_interrupts(priv); spin_unlock_irqrestore(&priv->low_lock, flags); + modify_acceptable_latency("ipw2100", INFINITE_LATENCY); + #ifdef ACPI_CSTATE_LIMIT_DEFINED if (priv->config & CFG_C3_DISABLED) { IPW_DEBUG_INFO(": Resetting C3 transitions.\n"); @@ -6534,6 +6542,7 @@ static int __init ipw2100_init(void) ret = pci_register_driver(&ipw2100_pci_driver); + set_acceptable_latency("ipw2100", INFINITE_LATENCY); #ifdef CONFIG_IPW2100_DEBUG ipw2100_debug_level = debug; driver_create_file(&ipw2100_pci_driver.driver, @@ -6554,6 +6563,7 @@ static void __exit ipw2100_exit(void) &driver_attr_debug_level); #endif pci_unregister_driver(&ipw2100_pci_driver); + remove_acceptable_latency("ipw2100"); } module_init(ipw2100_init); diff --git a/include/linux/latency.h b/include/linux/latency.h new file mode 100644 index 0000000000000..c08b52bb55b08 --- /dev/null +++ b/include/linux/latency.h @@ -0,0 +1,25 @@ +/* + * latency.h: Explicit system-wide latency-expectation infrastructure + * + * (C) Copyright 2006 Intel Corporation + * Author: Arjan van de Ven <arjan@linux.intel.com> + * + */ + +#ifndef _INCLUDE_GUARD_LATENCY_H_ +#define _INCLUDE_GUARD_LATENCY_H_ + +#include <linux/notifier.h> + +void set_acceptable_latency(char *identifier, int usecs); +void modify_acceptable_latency(char *identifier, int usecs); +void remove_acceptable_latency(char *identifier); +void synchronize_acceptable_latency(void); +int system_latency_constraint(void); + +int register_latency_notifier(struct notifier_block * nb); +int unregister_latency_notifier(struct notifier_block * nb); + +#define INFINITE_LATENCY 1000000 + +#endif diff --git a/kernel/Makefile b/kernel/Makefile index d62ec66c1af28..e210e8cf7237e 100644 --- a/kernel/Makefile +++ b/kernel/Makefile @@ -8,7 +8,7 @@ obj-y = sched.o fork.o exec_domain.o panic.o printk.o profile.o \ signal.o sys.o kmod.o workqueue.o pid.o \ rcupdate.o extable.o params.o posix-timers.o \ kthread.o wait.o kfifo.o sys_ni.o posix-cpu-timers.o mutex.o \ - hrtimer.o rwsem.o + hrtimer.o rwsem.o latency.o obj-$(CONFIG_STACKTRACE) += stacktrace.o obj-y += time/ diff --git a/kernel/latency.c b/kernel/latency.c new file mode 100644 index 0000000000000..258f2555abbc4 --- /dev/null +++ b/kernel/latency.c @@ -0,0 +1,279 @@ +/* + * latency.c: Explicit system-wide latency-expectation infrastructure + * + * The purpose of this infrastructure is to allow device drivers to set + * latency constraint they have and to collect and summarize these + * expectations globally. The cummulated result can then be used by + * power management and similar users to make decisions that have + * tradoffs with a latency component. + * + * An example user of this are the x86 C-states; each higher C state saves + * more power, but has a higher exit latency. For the idle loop power + * code to make a good decision which C-state to use, information about + * acceptable latencies is required. + * + * An example announcer of latency is an audio driver that knowns it + * will get an interrupt when the hardware has 200 usec of samples + * left in the DMA buffer; in that case the driver can set a latency + * constraint of, say, 150 usec. + * + * Multiple drivers can each announce their maximum accepted latency, + * to keep these appart, a string based identifier is used. + * + * + * (C) Copyright 2006 Intel Corporation + * Author: Arjan van de Ven <arjan@linux.intel.com> + * + * This program is free software; you can redistribute it and/or + * modify it under the terms of the GNU General Public License + * as published by the Free Software Foundation; version 2 + * of the License. + */ + +#include <linux/latency.h> +#include <linux/list.h> +#include <linux/spinlock.h> +#include <linux/slab.h> +#include <linux/module.h> +#include <linux/notifier.h> +#include <asm/atomic.h> + +struct latency_info { + struct list_head list; + int usecs; + char *identifier; +}; + +/* + * locking rule: all modifications to current_max_latency and + * latency_list need to be done while holding the latency_lock. + * latency_lock needs to be taken _irqsave. + */ +static atomic_t current_max_latency; +static DEFINE_SPINLOCK(latency_lock); + +static LIST_HEAD(latency_list); +static BLOCKING_NOTIFIER_HEAD(latency_notifier); + +/* + * This function returns the maximum latency allowed, which + * happens to be the minimum of all maximum latencies on the + * list. + */ +static int __find_max_latency(void) +{ + int min = INFINITE_LATENCY; + struct latency_info *info; + + list_for_each_entry(info, &latency_list, list) { + if (info->usecs < min) + min = info->usecs; + } + return min; +} + +/** + * set_acceptable_latency - sets the maximum latency acceptable + * @identifier: string that identifies this driver + * @usecs: maximum acceptable latency for this driver + * + * This function informs the kernel that this device(driver) + * can accept at most usecs latency. This setting is used for + * power management and similar tradeoffs. + * + * This function sleeps and can only be called from process + * context. + * Calling this function with an existing identifier is valid + * and will cause the existing latency setting to be changed. + */ +void set_acceptable_latency(char *identifier, int usecs) +{ + struct latency_info *info, *iter; + unsigned long flags; + int found_old = 0; + + info = kzalloc(sizeof(struct latency_info), GFP_KERNEL); + if (!info) + return; + info->usecs = usecs; + info->identifier = kstrdup(identifier, GFP_KERNEL); + if (!info->identifier) + goto free_info; + + spin_lock_irqsave(&latency_lock, flags); + list_for_each_entry(iter, &latency_list, list) { + if (strcmp(iter->identifier, identifier)==0) { + found_old = 1; + iter->usecs = usecs; + break; + } + } + if (!found_old) + list_add(&info->list, &latency_list); + + if (usecs < atomic_read(¤t_max_latency)) + atomic_set(¤t_max_latency, usecs); + + spin_unlock_irqrestore(&latency_lock, flags); + + blocking_notifier_call_chain(&latency_notifier, + atomic_read(¤t_max_latency), NULL); + + /* + * if we inserted the new one, we're done; otherwise there was + * an existing one so we need to free the redundant data + */ + if (!found_old) + return; + + kfree(info->identifier); +free_info: + kfree(info); +} +EXPORT_SYMBOL_GPL(set_acceptable_latency); + +/** + * modify_acceptable_latency - changes the maximum latency acceptable + * @identifier: string that identifies this driver + * @usecs: maximum acceptable latency for this driver + * + * This function informs the kernel that this device(driver) + * can accept at most usecs latency. This setting is used for + * power management and similar tradeoffs. + * + * This function does not sleep and can be called in any context. + * Trying to use a non-existing identifier silently gets ignored. + * + * Due to the atomic nature of this function, the modified latency + * value will only be used for future decisions; past decisions + * can still lead to longer latencies in the near future. + */ +void modify_acceptable_latency(char *identifier, int usecs) +{ + struct latency_info *iter; + unsigned long flags; + + spin_lock_irqsave(&latency_lock, flags); + list_for_each_entry(iter, &latency_list, list) { + if (strcmp(iter->identifier, identifier) == 0) { + iter->usecs = usecs; + break; + } + } + if (usecs < atomic_read(¤t_max_latency)) + atomic_set(¤t_max_latency, usecs); + spin_unlock_irqrestore(&latency_lock, flags); +} +EXPORT_SYMBOL_GPL(modify_acceptable_latency); + +/** + * remove_acceptable_latency - removes the maximum latency acceptable + * @identifier: string that identifies this driver + * + * This function removes a previously set maximum latency setting + * for the driver and frees up any resources associated with the + * bookkeeping needed for this. + * + * This function does not sleep and can be called in any context. + * Trying to use a non-existing identifier silently gets ignored. + */ +void remove_acceptable_latency(char *identifier) +{ + unsigned long flags; + int newmax = 0; + struct latency_info *iter, *temp; + + spin_lock_irqsave(&latency_lock, flags); + + list_for_each_entry_safe(iter, temp, &latency_list, list) { + if (strcmp(iter->identifier, identifier) == 0) { + list_del(&iter->list); + newmax = iter->usecs; + kfree(iter->identifier); + kfree(iter); + break; + } + } + + /* If we just deleted the system wide value, we need to + * recalculate with a full search + */ + if (newmax == atomic_read(¤t_max_latency)) { + newmax = __find_max_latency(); + atomic_set(¤t_max_latency, newmax); + } + spin_unlock_irqrestore(&latency_lock, flags); +} +EXPORT_SYMBOL_GPL(remove_acceptable_latency); + +/** + * system_latency_constraint - queries the system wide latency maximum + * + * This function returns the system wide maximum latency in + * microseconds. + * + * This function does not sleep and can be called in any context. + */ +int system_latency_constraint(void) +{ + return atomic_read(¤t_max_latency); +} +EXPORT_SYMBOL_GPL(system_latency_constraint); + +/** + * synchronize_acceptable_latency - recalculates all latency decisions + * + * This function will cause a callback to various kernel pieces that + * will make those pieces rethink their latency decisions. This implies + * that if there are overlong latencies in hardware state already, those + * latencies get taken right now. When this call completes no overlong + * latency decisions should be active anymore. + * + * Typical usecase of this is after a modify_acceptable_latency() call, + * which in itself is non-blocking and non-synchronizing. + * + * This function blocks and should not be called with locks held. + */ + +void synchronize_acceptable_latency(void) +{ + blocking_notifier_call_chain(&latency_notifier, + atomic_read(¤t_max_latency), NULL); +} +EXPORT_SYMBOL_GPL(synchronize_acceptable_latency); + +/* + * Latency notifier: this notifier gets called when a non-atomic new + * latency value gets set. The expectation nof the caller of the + * non-atomic set is that when the call returns, future latencies + * are within bounds, so the functions on the notifier list are + * expected to take the overlong latencies immediately, inside the + * callback, and not make a overlong latency decision anymore. + * + * The callback gets called when the new latency value is made + * active so system_latency_constraint() returns the new latency. + */ +int register_latency_notifier(struct notifier_block * nb) +{ + return blocking_notifier_chain_register(&latency_notifier, nb); +} +EXPORT_SYMBOL_GPL(register_latency_notifier); + +int unregister_latency_notifier(struct notifier_block * nb) +{ + return blocking_notifier_chain_unregister(&latency_notifier, nb); +} +EXPORT_SYMBOL_GPL(unregister_latency_notifier); + +static __init int latency_init(void) +{ + atomic_set(¤t_max_latency, INFINITE_LATENCY); + /* + * we don't want by default to have longer latencies than 2 ticks, + * since that would cause lost ticks + */ + set_acceptable_latency("kernel", 2*1000000/HZ); + return 0; +} + +module_init(latency_init); |