> That said, I have the feeling that is taking the wrong direction. Each time we > are entering idle, we check the latencies. Entering idle can be done thousand > of times per second. Wouldn't make sense to disable the states not fulfilling > the constraints at the moment the latencies are changed ? As the idle states > have increasing exit latencies, setting an idle state limit to disable all > states after that limit may be more efficient than checking again and again in > the idle path, no ?
You'r right. save some checking is good thing to do. >From 9e1cc3e02b8d954e606dd5a0f6466a8d5b3efab7 Mon Sep 17 00:00:00 2001 From: Alex Shi <[email protected]> Date: Wed, 26 Oct 2016 15:26:22 +0800 Subject: [PATCH 2/2] cpuidle/menu: add per cpu pm_qos_resume_latency consideration Kernel or user may have special requirement on cpu response time, like if a interrupt is pinned to a cpu, we don't want the cpu goes too deep sleep. This patch can prevent this thing happen by consider per cpu resume_latency setting in cpu sleep state selection in menu governor. The pm_qos_resume_latency ask device to give reponse in this time. That's similar with cpu cstates' entry_latency + exit_latency. But since most of cpu cstate either has no entry_latency or add it into exit_latency So, we just can restrict this time requirement as states exit_latency. We can set a wanted latency value according to the value of /sys/devices/system/cpu/cpuX/cpuidle/stateX/latency. to just a bit less than related state's latency value. Then cpu can get to this state or higher. Signed-off-by: Alex Shi <[email protected]> Acked-by: Rik van Riel <[email protected]> To: [email protected] Cc: [email protected] Cc: Ulf Hansson <[email protected]> Cc: Daniel Lezcano <[email protected]> Cc: Rasmus Villemoes <[email protected]> Cc: Arjan van de Ven <[email protected]> Cc: Rik van Riel <[email protected]> Cc: "Rafael J. Wysocki" <[email protected]> --- drivers/base/cpu.c | 2 ++ drivers/cpuidle/governors/menu.c | 10 ++++++++++ 2 files changed, 12 insertions(+) diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c index 4c28e1a..2c3b359 100644 --- a/drivers/base/cpu.c +++ b/drivers/base/cpu.c @@ -17,6 +17,7 @@ #include <linux/of.h> #include <linux/cpufeature.h> #include <linux/tick.h> +#include <linux/pm_qos.h> #include "base.h" @@ -376,6 +377,7 @@ int register_cpu(struct cpu *cpu, int num) per_cpu(cpu_sys_devices, num) = &cpu->dev; register_cpu_under_node(num, cpu_to_node(num)); + dev_pm_qos_expose_latency_limit(&cpu->dev, 0); return 0; } diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c index 07e36bb..cc7d873 100644 --- a/drivers/cpuidle/governors/menu.c +++ b/drivers/cpuidle/governors/menu.c @@ -19,6 +19,7 @@ #include <linux/tick.h> #include <linux/sched.h> #include <linux/math64.h> +#include <linux/cpu.h> /* * Please note when changing the tuning values: @@ -280,11 +281,13 @@ static unsigned int get_typical_interval(struct menu_device *data) static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev) { struct menu_device *data = this_cpu_ptr(&menu_devices); + struct device *device; int latency_req = pm_qos_request(PM_QOS_CPU_DMA_LATENCY); int i; unsigned int interactivity_req; unsigned int expected_interval; unsigned long nr_iowaiters, cpu_load; + int resume_latency; if (data->needs_update) { menu_update(drv, dev); @@ -295,6 +298,13 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev) if (unlikely(latency_req == 0)) return 0; + device = get_cpu_device(dev->cpu); + + /* resume_latency is 0 means no restriction */ + resume_latency = dev_pm_qos_read_value(device); + if (resume_latency) + latency_req = min(latency_req, resume_latency); + /* determine the expected residency time, round up */ data->next_timer_us = ktime_to_us(tick_nohz_get_sleep_length()); -- 2.8.1.101.g72d917a > > For example, a zero PM_QOS_CPU_DMA_LATENCY latency should prevent to enter the > select's idle routine. That's a good idea. I will give a draft change to review! :)
