diff options
Diffstat (limited to 'Documentation/power')
| -rw-r--r-- | Documentation/power/energy-model.rst | 183 | ||||
| -rw-r--r-- | Documentation/power/opp.rst | 2 | ||||
| -rw-r--r-- | Documentation/power/pci.rst | 2 | ||||
| -rw-r--r-- | Documentation/power/runtime_pm.rst | 23 | ||||
| -rw-r--r-- | Documentation/power/suspend-and-interrupts.rst | 2 |
5 files changed, 196 insertions, 16 deletions
diff --git a/Documentation/power/energy-model.rst b/Documentation/power/energy-model.rst index 13225965c9..ada4938c37 100644 --- a/Documentation/power/energy-model.rst +++ b/Documentation/power/energy-model.rst @@ -71,6 +71,31 @@ whose performance is scaled together. Performance domains generally have a required to have the same micro-architecture. CPUs in different performance domains can have different micro-architectures. +To better reflect power variation due to static power (leakage) the EM +supports runtime modifications of the power values. The mechanism relies on +RCU to free the modifiable EM perf_state table memory. Its user, the task +scheduler, also uses RCU to access this memory. The EM framework provides +API for allocating/freeing the new memory for the modifiable EM table. +The old memory is freed automatically using RCU callback mechanism when there +are no owners anymore for the given EM runtime table instance. This is tracked +using kref mechanism. The device driver which provided the new EM at runtime, +should call EM API to free it safely when it's no longer needed. The EM +framework will handle the clean-up when it's possible. + +The kernel code which want to modify the EM values is protected from concurrent +access using a mutex. Therefore, the device driver code must run in sleeping +context when it tries to modify the EM. + +With the runtime modifiable EM we switch from a 'single and during the entire +runtime static EM' (system property) design to a 'single EM which can be +changed during runtime according e.g. to the workload' (system and workload +property) design. + +It is possible also to modify the CPU performance values for each EM's +performance state. Thus, the full power and performance profile (which +is an exponential curve) can be changed according e.g. to the workload +or system property. + 2. Core APIs ------------ @@ -175,10 +200,82 @@ CPUfreq governor is in use in case of CPU device. Currently this calculation is not provided for other type of devices. More details about the above APIs can be found in ``<linux/energy_model.h>`` -or in Section 2.4 +or in Section 2.5 + + +2.4 Runtime modifications +^^^^^^^^^^^^^^^^^^^^^^^^^ + +Drivers willing to update the EM at runtime should use the following dedicated +function to allocate a new instance of the modified EM. The API is listed +below:: + + struct em_perf_table __rcu *em_table_alloc(struct em_perf_domain *pd); + +This allows to allocate a structure which contains the new EM table with +also RCU and kref needed by the EM framework. The 'struct em_perf_table' +contains array 'struct em_perf_state state[]' which is a list of performance +states in ascending order. That list must be populated by the device driver +which wants to update the EM. The list of frequencies can be taken from +existing EM (created during boot). The content in the 'struct em_perf_state' +must be populated by the driver as well. + +This is the API which does the EM update, using RCU pointers swap:: + + int em_dev_update_perf_domain(struct device *dev, + struct em_perf_table __rcu *new_table); + +Drivers must provide a pointer to the allocated and initialized new EM +'struct em_perf_table'. That new EM will be safely used inside the EM framework +and will be visible to other sub-systems in the kernel (thermal, powercap). +The main design goal for this API is to be fast and avoid extra calculations +or memory allocations at runtime. When pre-computed EMs are available in the +device driver, than it should be possible to simply re-use them with low +performance overhead. + +In order to free the EM, provided earlier by the driver (e.g. when the module +is unloaded), there is a need to call the API:: + + void em_table_free(struct em_perf_table __rcu *table); + +It will allow the EM framework to safely remove the memory, when there is +no other sub-system using it, e.g. EAS. + +To use the power values in other sub-systems (like thermal, powercap) there is +a need to call API which protects the reader and provide consistency of the EM +table data:: + + struct em_perf_state *em_perf_state_from_pd(struct em_perf_domain *pd); + +It returns the 'struct em_perf_state' pointer which is an array of performance +states in ascending order. +This function must be called in the RCU read lock section (after the +rcu_read_lock()). When the EM table is not needed anymore there is a need to +call rcu_real_unlock(). In this way the EM safely uses the RCU read section +and protects the users. It also allows the EM framework to manage the memory +and free it. More details how to use it can be found in Section 3.2 in the +example driver. + +There is dedicated API for device drivers to calculate em_perf_state::cost +values:: + + int em_dev_compute_costs(struct device *dev, struct em_perf_state *table, + int nr_states); + +These 'cost' values from EM are used in EAS. The new EM table should be passed +together with the number of entries and device pointer. When the computation +of the cost values is done properly the return value from the function is 0. +The function takes care for right setting of inefficiency for each performance +state as well. It updates em_perf_state::flags accordingly. +Then such prepared new EM can be passed to the em_dev_update_perf_domain() +function, which will allow to use it. + +More details about the above APIs can be found in ``<linux/energy_model.h>`` +or in Section 3.2 with an example code showing simple implementation of the +updating mechanism in a device driver. -2.4 Description details of this API +2.5 Description details of this API ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ .. kernel-doc:: include/linux/energy_model.h :internal: @@ -187,8 +284,11 @@ or in Section 2.4 :export: -3. Example driver ------------------ +3. Examples +----------- + +3.1 Example driver with EM registration +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ The CPUFreq framework supports dedicated callback for registering the EM for a given CPU(s) 'policy' object: cpufreq_driver::register_em(). @@ -242,3 +342,78 @@ EM framework:: 39 static struct cpufreq_driver foo_cpufreq_driver = { 40 .register_em = foo_cpufreq_register_em, 41 }; + + +3.2 Example driver with EM modification +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +This section provides a simple example of a thermal driver modifying the EM. +The driver implements a foo_thermal_em_update() function. The driver is woken +up periodically to check the temperature and modify the EM data:: + + -> drivers/soc/example/example_em_mod.c + + 01 static void foo_get_new_em(struct foo_context *ctx) + 02 { + 03 struct em_perf_table __rcu *em_table; + 04 struct em_perf_state *table, *new_table; + 05 struct device *dev = ctx->dev; + 06 struct em_perf_domain *pd; + 07 unsigned long freq; + 08 int i, ret; + 09 + 10 pd = em_pd_get(dev); + 11 if (!pd) + 12 return; + 13 + 14 em_table = em_table_alloc(pd); + 15 if (!em_table) + 16 return; + 17 + 18 new_table = em_table->state; + 19 + 20 rcu_read_lock(); + 21 table = em_perf_state_from_pd(pd); + 22 for (i = 0; i < pd->nr_perf_states; i++) { + 23 freq = table[i].frequency; + 24 foo_get_power_perf_values(dev, freq, &new_table[i]); + 25 } + 26 rcu_read_unlock(); + 27 + 28 /* Calculate 'cost' values for EAS */ + 29 ret = em_dev_compute_costs(dev, table, pd->nr_perf_states); + 30 if (ret) { + 31 dev_warn(dev, "EM: compute costs failed %d\n", ret); + 32 em_free_table(em_table); + 33 return; + 34 } + 35 + 36 ret = em_dev_update_perf_domain(dev, em_table); + 37 if (ret) { + 38 dev_warn(dev, "EM: update failed %d\n", ret); + 39 em_free_table(em_table); + 40 return; + 41 } + 42 + 43 /* + 44 * Since it's one-time-update drop the usage counter. + 45 * The EM framework will later free the table when needed. + 46 */ + 47 em_table_free(em_table); + 48 } + 49 + 50 /* + 51 * Function called periodically to check the temperature and + 52 * update the EM if needed + 53 */ + 54 static void foo_thermal_em_update(struct foo_context *ctx) + 55 { + 56 struct device *dev = ctx->dev; + 57 int cpu; + 58 + 59 ctx->temperature = foo_get_temp(dev, ctx); + 60 if (ctx->temperature < FOO_EM_UPDATE_TEMP_THRESHOLD) + 61 return; + 62 + 63 foo_get_new_em(ctx); + 64 } diff --git a/Documentation/power/opp.rst b/Documentation/power/opp.rst index a7c03c4709..1b7f1d854f 100644 --- a/Documentation/power/opp.rst +++ b/Documentation/power/opp.rst @@ -305,7 +305,7 @@ dev_pm_opp_get_opp_count { /* Do things */ num_available = dev_pm_opp_get_opp_count(dev); - speeds = kzalloc(sizeof(u32) * num_available, GFP_KERNEL); + speeds = kcalloc(num_available, sizeof(u32), GFP_KERNEL); /* populate the table in increasing order */ freq = 0; while (!IS_ERR(opp = dev_pm_opp_find_freq_ceil(dev, &freq))) { diff --git a/Documentation/power/pci.rst b/Documentation/power/pci.rst index a125544b4c..1207032030 100644 --- a/Documentation/power/pci.rst +++ b/Documentation/power/pci.rst @@ -625,7 +625,7 @@ The PCI subsystem-level callbacks they correspond to:: pci_pm_poweroff() pci_pm_poweroff_noirq() -work in analogy with pci_pm_suspend() and pci_pm_poweroff_noirq(), respectively, +work in analogy with pci_pm_suspend() and pci_pm_suspend_noirq(), respectively, although they don't attempt to save the device's standard configuration registers. diff --git a/Documentation/power/runtime_pm.rst b/Documentation/power/runtime_pm.rst index 65b86e487a..5c4e730f38 100644 --- a/Documentation/power/runtime_pm.rst +++ b/Documentation/power/runtime_pm.rst @@ -154,7 +154,7 @@ suspending the device are satisfied) and to queue up a suspend request for the device in that case. If there is no idle callback, or if the callback returns 0, then the PM core will attempt to carry out a runtime suspend of the device, also respecting devices configured for autosuspend. In essence this means a -call to pm_runtime_autosuspend() (do note that drivers needs to update the +call to __pm_runtime_autosuspend() (do note that drivers needs to update the device last busy mark, pm_runtime_mark_last_busy(), to control the delay under this circumstance). To prevent this (for example, if the callback routine has started a delayed suspend), the routine must return a non-zero value. Negative @@ -396,10 +396,9 @@ drivers/base/power/runtime.c and include/linux/pm_runtime.h: nonzero, increment the counter and return 1; otherwise return 0 without changing the counter - `int pm_runtime_get_if_active(struct device *dev, bool ign_usage_count);` + `int pm_runtime_get_if_active(struct device *dev);` - return -EINVAL if 'power.disable_depth' is nonzero; otherwise, if the - runtime PM status is RPM_ACTIVE, and either ign_usage_count is true - or the device's usage_count is non-zero, increment the counter and + runtime PM status is RPM_ACTIVE, increment the counter and return 1; otherwise return 0 without changing the counter `void pm_runtime_put_noidle(struct device *dev);` @@ -410,6 +409,10 @@ drivers/base/power/runtime.c and include/linux/pm_runtime.h: pm_request_idle(dev) and return its result `int pm_runtime_put_autosuspend(struct device *dev);` + - does the same as __pm_runtime_put_autosuspend() for now, but in the + future, will also call pm_runtime_mark_last_busy() as well, DO NOT USE! + + `int __pm_runtime_put_autosuspend(struct device *dev);` - decrement the device's usage counter; if the result is 0 then run pm_request_autosuspend(dev) and return its result @@ -540,6 +543,7 @@ It is safe to execute the following helper functions from interrupt context: - pm_runtime_put_noidle() - pm_runtime_put() - pm_runtime_put_autosuspend() +- __pm_runtime_put_autosuspend() - pm_runtime_enable() - pm_suspend_ignore_children() - pm_runtime_set_active() @@ -730,6 +734,7 @@ out the following operations: for it, respectively. 7. Generic subsystem callbacks +============================== Subsystems may wish to conserve code space by using the set of generic power management callbacks provided by the PM core, defined in @@ -865,9 +870,9 @@ automatically be delayed until the desired period of inactivity has elapsed. Inactivity is determined based on the power.last_busy field. Drivers should call pm_runtime_mark_last_busy() to update this field after carrying out I/O, -typically just before calling pm_runtime_put_autosuspend(). The desired length -of the inactivity period is a matter of policy. Subsystems can set this length -initially by calling pm_runtime_set_autosuspend_delay(), but after device +typically just before calling __pm_runtime_put_autosuspend(). The desired +length of the inactivity period is a matter of policy. Subsystems can set this +length initially by calling pm_runtime_set_autosuspend_delay(), but after device registration the length should be controlled by user space, using the /sys/devices/.../power/autosuspend_delay_ms attribute. @@ -878,7 +883,7 @@ instead of the non-autosuspend counterparts:: Instead of: pm_runtime_suspend use: pm_runtime_autosuspend; Instead of: pm_schedule_suspend use: pm_request_autosuspend; - Instead of: pm_runtime_put use: pm_runtime_put_autosuspend; + Instead of: pm_runtime_put use: __pm_runtime_put_autosuspend; Instead of: pm_runtime_put_sync use: pm_runtime_put_sync_autosuspend. Drivers may also continue to use the non-autosuspend helper functions; they @@ -917,7 +922,7 @@ Here is a schematic pseudo-code example:: lock(&foo->private_lock); if (--foo->num_pending_requests == 0) { pm_runtime_mark_last_busy(&foo->dev); - pm_runtime_put_autosuspend(&foo->dev); + __pm_runtime_put_autosuspend(&foo->dev); } else { foo_process_next_request(foo); } diff --git a/Documentation/power/suspend-and-interrupts.rst b/Documentation/power/suspend-and-interrupts.rst index dfbace2f46..f588feeeca 100644 --- a/Documentation/power/suspend-and-interrupts.rst +++ b/Documentation/power/suspend-and-interrupts.rst @@ -78,7 +78,7 @@ handling the given IRQ as a system wakeup interrupt line and disable_irq_wake() turns that logic off. Calling enable_irq_wake() causes suspend_device_irqs() to treat the given IRQ -in a special way. Namely, the IRQ remains enabled, by on the first interrupt +in a special way. Namely, the IRQ remains enabled, but on the first interrupt it will be disabled, marked as pending and "suspended" so that it will be re-enabled by resume_device_irqs() during the subsequent system resume. Also the PM core is notified about the event which causes the system suspend in |