578 строки
18 KiB
C
578 строки
18 KiB
C
/*
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* menu.c - the menu idle governor
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*
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* Copyright (C) 2006-2007 Adam Belay <abelay@novell.com>
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* Copyright (C) 2009 Intel Corporation
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* Author:
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* Arjan van de Ven <arjan@linux.intel.com>
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*
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* This code is licenced under the GPL version 2 as described
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* in the COPYING file that acompanies the Linux Kernel.
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*/
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#include <linux/kernel.h>
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#include <linux/cpuidle.h>
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#include <linux/time.h>
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#include <linux/ktime.h>
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#include <linux/hrtimer.h>
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#include <linux/tick.h>
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#include <linux/sched.h>
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#include <linux/sched/loadavg.h>
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#include <linux/sched/stat.h>
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#include <linux/math64.h>
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/*
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* Please note when changing the tuning values:
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* If (MAX_INTERESTING-1) * RESOLUTION > UINT_MAX, the result of
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* a scaling operation multiplication may overflow on 32 bit platforms.
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* In that case, #define RESOLUTION as ULL to get 64 bit result:
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* #define RESOLUTION 1024ULL
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*
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* The default values do not overflow.
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*/
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#define BUCKETS 12
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#define INTERVAL_SHIFT 3
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#define INTERVALS (1UL << INTERVAL_SHIFT)
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#define RESOLUTION 1024
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#define DECAY 8
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#define MAX_INTERESTING 50000
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/*
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* Concepts and ideas behind the menu governor
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*
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* For the menu governor, there are 3 decision factors for picking a C
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* state:
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* 1) Energy break even point
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* 2) Performance impact
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* 3) Latency tolerance (from pmqos infrastructure)
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* These these three factors are treated independently.
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*
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* Energy break even point
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* -----------------------
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* C state entry and exit have an energy cost, and a certain amount of time in
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* the C state is required to actually break even on this cost. CPUIDLE
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* provides us this duration in the "target_residency" field. So all that we
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* need is a good prediction of how long we'll be idle. Like the traditional
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* menu governor, we start with the actual known "next timer event" time.
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*
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* Since there are other source of wakeups (interrupts for example) than
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* the next timer event, this estimation is rather optimistic. To get a
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* more realistic estimate, a correction factor is applied to the estimate,
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* that is based on historic behavior. For example, if in the past the actual
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* duration always was 50% of the next timer tick, the correction factor will
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* be 0.5.
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*
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* menu uses a running average for this correction factor, however it uses a
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* set of factors, not just a single factor. This stems from the realization
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* that the ratio is dependent on the order of magnitude of the expected
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* duration; if we expect 500 milliseconds of idle time the likelihood of
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* getting an interrupt very early is much higher than if we expect 50 micro
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* seconds of idle time. A second independent factor that has big impact on
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* the actual factor is if there is (disk) IO outstanding or not.
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* (as a special twist, we consider every sleep longer than 50 milliseconds
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* as perfect; there are no power gains for sleeping longer than this)
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*
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* For these two reasons we keep an array of 12 independent factors, that gets
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* indexed based on the magnitude of the expected duration as well as the
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* "is IO outstanding" property.
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*
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* Repeatable-interval-detector
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* ----------------------------
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* There are some cases where "next timer" is a completely unusable predictor:
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* Those cases where the interval is fixed, for example due to hardware
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* interrupt mitigation, but also due to fixed transfer rate devices such as
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* mice.
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* For this, we use a different predictor: We track the duration of the last 8
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* intervals and if the stand deviation of these 8 intervals is below a
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* threshold value, we use the average of these intervals as prediction.
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*
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* Limiting Performance Impact
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* ---------------------------
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* C states, especially those with large exit latencies, can have a real
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* noticeable impact on workloads, which is not acceptable for most sysadmins,
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* and in addition, less performance has a power price of its own.
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*
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* As a general rule of thumb, menu assumes that the following heuristic
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* holds:
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* The busier the system, the less impact of C states is acceptable
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*
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* This rule-of-thumb is implemented using a performance-multiplier:
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* If the exit latency times the performance multiplier is longer than
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* the predicted duration, the C state is not considered a candidate
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* for selection due to a too high performance impact. So the higher
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* this multiplier is, the longer we need to be idle to pick a deep C
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* state, and thus the less likely a busy CPU will hit such a deep
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* C state.
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*
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* Two factors are used in determing this multiplier:
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* a value of 10 is added for each point of "per cpu load average" we have.
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* a value of 5 points is added for each process that is waiting for
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* IO on this CPU.
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* (these values are experimentally determined)
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*
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* The load average factor gives a longer term (few seconds) input to the
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* decision, while the iowait value gives a cpu local instantanious input.
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* The iowait factor may look low, but realize that this is also already
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* represented in the system load average.
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*
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*/
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struct menu_device {
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int last_state_idx;
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int needs_update;
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int tick_wakeup;
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unsigned int next_timer_us;
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unsigned int predicted_us;
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unsigned int bucket;
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unsigned int correction_factor[BUCKETS];
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unsigned int intervals[INTERVALS];
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int interval_ptr;
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};
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#define LOAD_INT(x) ((x) >> FSHIFT)
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#define LOAD_FRAC(x) LOAD_INT(((x) & (FIXED_1-1)) * 100)
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static inline int get_loadavg(unsigned long load)
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{
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return LOAD_INT(load) * 10 + LOAD_FRAC(load) / 10;
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}
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static inline int which_bucket(unsigned int duration, unsigned long nr_iowaiters)
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{
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int bucket = 0;
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/*
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* We keep two groups of stats; one with no
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* IO pending, one without.
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* This allows us to calculate
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* E(duration)|iowait
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*/
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if (nr_iowaiters)
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bucket = BUCKETS/2;
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if (duration < 10)
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return bucket;
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if (duration < 100)
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return bucket + 1;
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if (duration < 1000)
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return bucket + 2;
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if (duration < 10000)
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return bucket + 3;
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if (duration < 100000)
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return bucket + 4;
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return bucket + 5;
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}
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/*
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* Return a multiplier for the exit latency that is intended
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* to take performance requirements into account.
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* The more performance critical we estimate the system
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* to be, the higher this multiplier, and thus the higher
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* the barrier to go to an expensive C state.
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*/
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static inline int performance_multiplier(unsigned long nr_iowaiters, unsigned long load)
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{
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int mult = 1;
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/* for higher loadavg, we are more reluctant */
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mult += 2 * get_loadavg(load);
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/* for IO wait tasks (per cpu!) we add 5x each */
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mult += 10 * nr_iowaiters;
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return mult;
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}
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static DEFINE_PER_CPU(struct menu_device, menu_devices);
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static void menu_update(struct cpuidle_driver *drv, struct cpuidle_device *dev);
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/*
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* Try detecting repeating patterns by keeping track of the last 8
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* intervals, and checking if the standard deviation of that set
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* of points is below a threshold. If it is... then use the
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* average of these 8 points as the estimated value.
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*/
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static unsigned int get_typical_interval(struct menu_device *data)
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{
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int i, divisor;
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unsigned int max, thresh, avg;
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uint64_t sum, variance;
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thresh = UINT_MAX; /* Discard outliers above this value */
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again:
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/* First calculate the average of past intervals */
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max = 0;
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sum = 0;
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divisor = 0;
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for (i = 0; i < INTERVALS; i++) {
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unsigned int value = data->intervals[i];
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if (value <= thresh) {
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sum += value;
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divisor++;
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if (value > max)
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max = value;
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}
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}
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if (divisor == INTERVALS)
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avg = sum >> INTERVAL_SHIFT;
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else
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avg = div_u64(sum, divisor);
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/* Then try to determine variance */
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variance = 0;
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for (i = 0; i < INTERVALS; i++) {
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unsigned int value = data->intervals[i];
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if (value <= thresh) {
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int64_t diff = (int64_t)value - avg;
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variance += diff * diff;
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}
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}
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if (divisor == INTERVALS)
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variance >>= INTERVAL_SHIFT;
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else
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do_div(variance, divisor);
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/*
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* The typical interval is obtained when standard deviation is
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* small (stddev <= 20 us, variance <= 400 us^2) or standard
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* deviation is small compared to the average interval (avg >
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* 6*stddev, avg^2 > 36*variance). The average is smaller than
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* UINT_MAX aka U32_MAX, so computing its square does not
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* overflow a u64. We simply reject this candidate average if
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* the standard deviation is greater than 715 s (which is
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* rather unlikely).
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*
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* Use this result only if there is no timer to wake us up sooner.
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*/
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if (likely(variance <= U64_MAX/36)) {
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if ((((u64)avg*avg > variance*36) && (divisor * 4 >= INTERVALS * 3))
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|| variance <= 400) {
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return avg;
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}
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}
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/*
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* If we have outliers to the upside in our distribution, discard
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* those by setting the threshold to exclude these outliers, then
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* calculate the average and standard deviation again. Once we get
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* down to the bottom 3/4 of our samples, stop excluding samples.
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*
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* This can deal with workloads that have long pauses interspersed
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* with sporadic activity with a bunch of short pauses.
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*/
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if ((divisor * 4) <= INTERVALS * 3)
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return UINT_MAX;
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thresh = max - 1;
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goto again;
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}
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/**
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* menu_select - selects the next idle state to enter
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* @drv: cpuidle driver containing state data
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* @dev: the CPU
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* @stop_tick: indication on whether or not to stop the tick
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*/
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static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev,
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bool *stop_tick)
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{
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struct menu_device *data = this_cpu_ptr(&menu_devices);
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int latency_req = cpuidle_governor_latency_req(dev->cpu);
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int i;
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int first_idx;
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int idx;
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unsigned int interactivity_req;
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unsigned int expected_interval;
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unsigned long nr_iowaiters, cpu_load;
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ktime_t delta_next;
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if (data->needs_update) {
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menu_update(drv, dev);
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data->needs_update = 0;
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}
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/* Special case when user has set very strict latency requirement */
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if (unlikely(latency_req == 0)) {
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*stop_tick = false;
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return 0;
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}
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/* determine the expected residency time, round up */
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data->next_timer_us = ktime_to_us(tick_nohz_get_sleep_length(&delta_next));
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get_iowait_load(&nr_iowaiters, &cpu_load);
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data->bucket = which_bucket(data->next_timer_us, nr_iowaiters);
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/*
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* Force the result of multiplication to be 64 bits even if both
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* operands are 32 bits.
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* Make sure to round up for half microseconds.
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*/
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data->predicted_us = DIV_ROUND_CLOSEST_ULL((uint64_t)data->next_timer_us *
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data->correction_factor[data->bucket],
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RESOLUTION * DECAY);
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expected_interval = get_typical_interval(data);
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expected_interval = min(expected_interval, data->next_timer_us);
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first_idx = 0;
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if (drv->states[0].flags & CPUIDLE_FLAG_POLLING) {
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struct cpuidle_state *s = &drv->states[1];
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unsigned int polling_threshold;
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/*
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* We want to default to C1 (hlt), not to busy polling
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* unless the timer is happening really really soon, or
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* C1's exit latency exceeds the user configured limit.
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*/
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polling_threshold = max_t(unsigned int, 20, s->target_residency);
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if (data->next_timer_us > polling_threshold &&
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latency_req > s->exit_latency && !s->disabled &&
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!dev->states_usage[1].disable)
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first_idx = 1;
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}
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/*
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* Use the lowest expected idle interval to pick the idle state.
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*/
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data->predicted_us = min(data->predicted_us, expected_interval);
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if (tick_nohz_tick_stopped()) {
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/*
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* If the tick is already stopped, the cost of possible short
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* idle duration misprediction is much higher, because the CPU
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* may be stuck in a shallow idle state for a long time as a
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* result of it. In that case say we might mispredict and try
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* to force the CPU into a state for which we would have stopped
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* the tick, unless a timer is going to expire really soon
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* anyway.
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*/
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if (data->predicted_us < TICK_USEC)
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data->predicted_us = min_t(unsigned int, TICK_USEC,
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ktime_to_us(delta_next));
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} else {
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/*
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* Use the performance multiplier and the user-configurable
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* latency_req to determine the maximum exit latency.
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*/
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interactivity_req = data->predicted_us / performance_multiplier(nr_iowaiters, cpu_load);
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if (latency_req > interactivity_req)
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latency_req = interactivity_req;
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}
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expected_interval = data->predicted_us;
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/*
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* Find the idle state with the lowest power while satisfying
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* our constraints.
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*/
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idx = -1;
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for (i = first_idx; i < drv->state_count; i++) {
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struct cpuidle_state *s = &drv->states[i];
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struct cpuidle_state_usage *su = &dev->states_usage[i];
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if (s->disabled || su->disable)
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continue;
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if (idx == -1)
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idx = i; /* first enabled state */
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if (s->target_residency > data->predicted_us)
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break;
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if (s->exit_latency > latency_req) {
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/*
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* If we break out of the loop for latency reasons, use
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* the target residency of the selected state as the
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* expected idle duration so that the tick is retained
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* as long as that target residency is low enough.
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*/
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expected_interval = drv->states[idx].target_residency;
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break;
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}
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idx = i;
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}
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if (idx == -1)
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idx = 0; /* No states enabled. Must use 0. */
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/*
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* Don't stop the tick if the selected state is a polling one or if the
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* expected idle duration is shorter than the tick period length.
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*/
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if ((drv->states[idx].flags & CPUIDLE_FLAG_POLLING) ||
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expected_interval < TICK_USEC) {
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unsigned int delta_next_us = ktime_to_us(delta_next);
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*stop_tick = false;
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if (!tick_nohz_tick_stopped() && idx > 0 &&
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drv->states[idx].target_residency > delta_next_us) {
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/*
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* The tick is not going to be stopped and the target
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* residency of the state to be returned is not within
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* the time until the next timer event including the
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* tick, so try to correct that.
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*/
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for (i = idx - 1; i >= 0; i--) {
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if (drv->states[i].disabled ||
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dev->states_usage[i].disable)
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continue;
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idx = i;
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if (drv->states[i].target_residency <= delta_next_us)
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break;
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}
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}
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}
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data->last_state_idx = idx;
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return data->last_state_idx;
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}
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/**
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* menu_reflect - records that data structures need update
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* @dev: the CPU
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* @index: the index of actual entered state
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*
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* NOTE: it's important to be fast here because this operation will add to
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* the overall exit latency.
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*/
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static void menu_reflect(struct cpuidle_device *dev, int index)
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{
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struct menu_device *data = this_cpu_ptr(&menu_devices);
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data->last_state_idx = index;
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data->needs_update = 1;
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data->tick_wakeup = tick_nohz_idle_got_tick();
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}
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/**
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* menu_update - attempts to guess what happened after entry
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* @drv: cpuidle driver containing state data
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* @dev: the CPU
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*/
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static void menu_update(struct cpuidle_driver *drv, struct cpuidle_device *dev)
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{
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struct menu_device *data = this_cpu_ptr(&menu_devices);
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int last_idx = data->last_state_idx;
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struct cpuidle_state *target = &drv->states[last_idx];
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unsigned int measured_us;
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unsigned int new_factor;
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/*
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* Try to figure out how much time passed between entry to low
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* power state and occurrence of the wakeup event.
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*
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* If the entered idle state didn't support residency measurements,
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* we use them anyway if they are short, and if long,
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* truncate to the whole expected time.
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*
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* Any measured amount of time will include the exit latency.
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* Since we are interested in when the wakeup begun, not when it
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* was completed, we must subtract the exit latency. However, if
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* the measured amount of time is less than the exit latency,
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* assume the state was never reached and the exit latency is 0.
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*/
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if (data->tick_wakeup && data->next_timer_us > TICK_USEC) {
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/*
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* The nohz code said that there wouldn't be any events within
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* the tick boundary (if the tick was stopped), but the idle
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* duration predictor had a differing opinion. Since the CPU
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* was woken up by a tick (that wasn't stopped after all), the
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* predictor was not quite right, so assume that the CPU could
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* have been idle long (but not forever) to help the idle
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* duration predictor do a better job next time.
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*/
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measured_us = 9 * MAX_INTERESTING / 10;
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} else {
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/* measured value */
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measured_us = cpuidle_get_last_residency(dev);
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/* Deduct exit latency */
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if (measured_us > 2 * target->exit_latency)
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measured_us -= target->exit_latency;
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else
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measured_us /= 2;
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}
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/* Make sure our coefficients do not exceed unity */
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if (measured_us > data->next_timer_us)
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measured_us = data->next_timer_us;
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/* Update our correction ratio */
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new_factor = data->correction_factor[data->bucket];
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new_factor -= new_factor / DECAY;
|
|
|
|
if (data->next_timer_us > 0 && measured_us < MAX_INTERESTING)
|
|
new_factor += RESOLUTION * measured_us / data->next_timer_us;
|
|
else
|
|
/*
|
|
* we were idle so long that we count it as a perfect
|
|
* prediction
|
|
*/
|
|
new_factor += RESOLUTION;
|
|
|
|
/*
|
|
* We don't want 0 as factor; we always want at least
|
|
* a tiny bit of estimated time. Fortunately, due to rounding,
|
|
* new_factor will stay nonzero regardless of measured_us values
|
|
* and the compiler can eliminate this test as long as DECAY > 1.
|
|
*/
|
|
if (DECAY == 1 && unlikely(new_factor == 0))
|
|
new_factor = 1;
|
|
|
|
data->correction_factor[data->bucket] = new_factor;
|
|
|
|
/* update the repeating-pattern data */
|
|
data->intervals[data->interval_ptr++] = measured_us;
|
|
if (data->interval_ptr >= INTERVALS)
|
|
data->interval_ptr = 0;
|
|
}
|
|
|
|
/**
|
|
* menu_enable_device - scans a CPU's states and does setup
|
|
* @drv: cpuidle driver
|
|
* @dev: the CPU
|
|
*/
|
|
static int menu_enable_device(struct cpuidle_driver *drv,
|
|
struct cpuidle_device *dev)
|
|
{
|
|
struct menu_device *data = &per_cpu(menu_devices, dev->cpu);
|
|
int i;
|
|
|
|
memset(data, 0, sizeof(struct menu_device));
|
|
|
|
/*
|
|
* if the correction factor is 0 (eg first time init or cpu hotplug
|
|
* etc), we actually want to start out with a unity factor.
|
|
*/
|
|
for(i = 0; i < BUCKETS; i++)
|
|
data->correction_factor[i] = RESOLUTION * DECAY;
|
|
|
|
return 0;
|
|
}
|
|
|
|
static struct cpuidle_governor menu_governor = {
|
|
.name = "menu",
|
|
.rating = 20,
|
|
.enable = menu_enable_device,
|
|
.select = menu_select,
|
|
.reflect = menu_reflect,
|
|
};
|
|
|
|
/**
|
|
* init_menu - initializes the governor
|
|
*/
|
|
static int __init init_menu(void)
|
|
{
|
|
return cpuidle_register_governor(&menu_governor);
|
|
}
|
|
|
|
postcore_initcall(init_menu);
|