blob: aa4eeaa703ad4a35ef017093bf1089eb40b7497a [file] [log] [blame]
/*
* Pressure stall information for CPU, memory and IO
*
* Copyright (c) 2018 Facebook, Inc.
* Author: Johannes Weiner <hannes@cmpxchg.org>
*
* Polling support by Suren Baghdasaryan <surenb@google.com>
* Copyright (c) 2018 Google, Inc.
*
* When CPU, memory and IO are contended, tasks experience delays that
* reduce throughput and introduce latencies into the workload. Memory
* and IO contention, in addition, can cause a full loss of forward
* progress in which the CPU goes idle.
*
* This code aggregates individual task delays into resource pressure
* metrics that indicate problems with both workload health and
* resource utilization.
*
* Model
*
* The time in which a task can execute on a CPU is our baseline for
* productivity. Pressure expresses the amount of time in which this
* potential cannot be realized due to resource contention.
*
* This concept of productivity has two components: the workload and
* the CPU. To measure the impact of pressure on both, we define two
* contention states for a resource: SOME and FULL.
*
* In the SOME state of a given resource, one or more tasks are
* delayed on that resource. This affects the workload's ability to
* perform work, but the CPU may still be executing other tasks.
*
* In the FULL state of a given resource, all non-idle tasks are
* delayed on that resource such that nobody is advancing and the CPU
* goes idle. This leaves both workload and CPU unproductive.
*
* (Naturally, the FULL state doesn't exist for the CPU resource.)
*
* SOME = nr_delayed_tasks != 0
* FULL = nr_delayed_tasks != 0 && nr_running_tasks == 0
*
* The percentage of wallclock time spent in those compound stall
* states gives pressure numbers between 0 and 100 for each resource,
* where the SOME percentage indicates workload slowdowns and the FULL
* percentage indicates reduced CPU utilization:
*
* %SOME = time(SOME) / period
* %FULL = time(FULL) / period
*
* Multiple CPUs
*
* The more tasks and available CPUs there are, the more work can be
* performed concurrently. This means that the potential that can go
* unrealized due to resource contention *also* scales with non-idle
* tasks and CPUs.
*
* Consider a scenario where 257 number crunching tasks are trying to
* run concurrently on 256 CPUs. If we simply aggregated the task
* states, we would have to conclude a CPU SOME pressure number of
* 100%, since *somebody* is waiting on a runqueue at all
* times. However, that is clearly not the amount of contention the
* workload is experiencing: only one out of 256 possible exceution
* threads will be contended at any given time, or about 0.4%.
*
* Conversely, consider a scenario of 4 tasks and 4 CPUs where at any
* given time *one* of the tasks is delayed due to a lack of memory.
* Again, looking purely at the task state would yield a memory FULL
* pressure number of 0%, since *somebody* is always making forward
* progress. But again this wouldn't capture the amount of execution
* potential lost, which is 1 out of 4 CPUs, or 25%.
*
* To calculate wasted potential (pressure) with multiple processors,
* we have to base our calculation on the number of non-idle tasks in
* conjunction with the number of available CPUs, which is the number
* of potential execution threads. SOME becomes then the proportion of
* delayed tasks to possibe threads, and FULL is the share of possible
* threads that are unproductive due to delays:
*
* threads = min(nr_nonidle_tasks, nr_cpus)
* SOME = min(nr_delayed_tasks / threads, 1)
* FULL = (threads - min(nr_running_tasks, threads)) / threads
*
* For the 257 number crunchers on 256 CPUs, this yields:
*
* threads = min(257, 256)
* SOME = min(1 / 256, 1) = 0.4%
* FULL = (256 - min(257, 256)) / 256 = 0%
*
* For the 1 out of 4 memory-delayed tasks, this yields:
*
* threads = min(4, 4)
* SOME = min(1 / 4, 1) = 25%
* FULL = (4 - min(3, 4)) / 4 = 25%
*
* [ Substitute nr_cpus with 1, and you can see that it's a natural
* extension of the single-CPU model. ]
*
* Implementation
*
* To assess the precise time spent in each such state, we would have
* to freeze the system on task changes and start/stop the state
* clocks accordingly. Obviously that doesn't scale in practice.
*
* Because the scheduler aims to distribute the compute load evenly
* among the available CPUs, we can track task state locally to each
* CPU and, at much lower frequency, extrapolate the global state for
* the cumulative stall times and the running averages.
*
* For each runqueue, we track:
*
* tSOME[cpu] = time(nr_delayed_tasks[cpu] != 0)
* tFULL[cpu] = time(nr_delayed_tasks[cpu] && !nr_running_tasks[cpu])
* tNONIDLE[cpu] = time(nr_nonidle_tasks[cpu] != 0)
*
* and then periodically aggregate:
*
* tNONIDLE = sum(tNONIDLE[i])
*
* tSOME = sum(tSOME[i] * tNONIDLE[i]) / tNONIDLE
* tFULL = sum(tFULL[i] * tNONIDLE[i]) / tNONIDLE
*
* %SOME = tSOME / period
* %FULL = tFULL / period
*
* This gives us an approximation of pressure that is practical
* cost-wise, yet way more sensitive and accurate than periodic
* sampling of the aggregate task states would be.
*/
#include "../workqueue_internal.h"
#include <linux/sched/loadavg.h>
#include <linux/seq_file.h>
#include <linux/proc_fs.h>
#include <linux/seqlock.h>
#include <linux/uaccess.h>
#include <linux/cgroup.h>
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/ctype.h>
#include <linux/file.h>
#include <linux/poll.h>
#include <linux/psi.h>
#include "sched.h"
static int psi_bug __read_mostly;
DEFINE_STATIC_KEY_FALSE(psi_disabled);
#ifdef CONFIG_PSI_DEFAULT_DISABLED
static bool psi_enable;
#else
static bool psi_enable = true;
#endif
static int __init setup_psi(char *str)
{
return kstrtobool(str, &psi_enable) == 0;
}
__setup("psi=", setup_psi);
/* Running averages - we need to be higher-res than loadavg */
#define PSI_FREQ (2*HZ+1) /* 2 sec intervals */
#define EXP_10s 1677 /* 1/exp(2s/10s) as fixed-point */
#define EXP_60s 1981 /* 1/exp(2s/60s) */
#define EXP_300s 2034 /* 1/exp(2s/300s) */
/* PSI trigger definitions */
#define WINDOW_MIN_US 500000 /* Min window size is 500ms */
#define WINDOW_MAX_US 10000000 /* Max window size is 10s */
#define UPDATES_PER_WINDOW 10 /* 10 updates per window */
/* Sampling frequency in nanoseconds */
static u64 psi_period __read_mostly;
/* System-level pressure and stall tracking */
static DEFINE_PER_CPU(struct psi_group_cpu, system_group_pcpu);
static struct psi_group psi_system = {
.pcpu = &system_group_pcpu,
};
static void psi_avgs_work(struct work_struct *work);
static void group_init(struct psi_group *group)
{
int cpu;
for_each_possible_cpu(cpu)
seqcount_init(&per_cpu_ptr(group->pcpu, cpu)->seq);
group->avg_next_update = sched_clock() + psi_period;
INIT_DELAYED_WORK(&group->avgs_work, psi_avgs_work);
mutex_init(&group->avgs_lock);
/* Init trigger-related members */
atomic_set(&group->poll_scheduled, 0);
mutex_init(&group->trigger_lock);
INIT_LIST_HEAD(&group->triggers);
memset(group->nr_triggers, 0, sizeof(group->nr_triggers));
group->poll_states = 0;
group->poll_min_period = U32_MAX;
memset(group->polling_total, 0, sizeof(group->polling_total));
group->polling_next_update = ULLONG_MAX;
group->polling_until = 0;
rcu_assign_pointer(group->poll_kworker, NULL);
}
void __init psi_init(void)
{
if (!psi_enable) {
static_branch_enable(&psi_disabled);
return;
}
psi_period = jiffies_to_nsecs(PSI_FREQ);
group_init(&psi_system);
}
static bool test_state(unsigned int *tasks, enum psi_states state)
{
switch (state) {
case PSI_IO_SOME:
return tasks[NR_IOWAIT];
case PSI_IO_FULL:
return tasks[NR_IOWAIT] && !tasks[NR_RUNNING];
case PSI_MEM_SOME:
return tasks[NR_MEMSTALL];
case PSI_MEM_FULL:
return tasks[NR_MEMSTALL] && !tasks[NR_RUNNING];
case PSI_CPU_SOME:
return tasks[NR_RUNNING] > 1;
case PSI_NONIDLE:
return tasks[NR_IOWAIT] || tasks[NR_MEMSTALL] ||
tasks[NR_RUNNING];
default:
return false;
}
}
static void get_recent_times(struct psi_group *group, int cpu,
enum psi_aggregators aggregator, u32 *times,
u32 *pchanged_states)
{
struct psi_group_cpu *groupc = per_cpu_ptr(group->pcpu, cpu);
u64 now, state_start;
enum psi_states s;
unsigned int seq;
u32 state_mask;
*pchanged_states = 0;
/* Snapshot a coherent view of the CPU state */
do {
seq = read_seqcount_begin(&groupc->seq);
now = cpu_clock(cpu);
memcpy(times, groupc->times, sizeof(groupc->times));
state_mask = groupc->state_mask;
state_start = groupc->state_start;
} while (read_seqcount_retry(&groupc->seq, seq));
/* Calculate state time deltas against the previous snapshot */
for (s = 0; s < NR_PSI_STATES; s++) {
u32 delta;
/*
* In addition to already concluded states, we also
* incorporate currently active states on the CPU,
* since states may last for many sampling periods.
*
* This way we keep our delta sampling buckets small
* (u32) and our reported pressure close to what's
* actually happening.
*/
if (state_mask & (1 << s))
times[s] += now - state_start;
delta = times[s] - groupc->times_prev[aggregator][s];
groupc->times_prev[aggregator][s] = times[s];
times[s] = delta;
if (delta)
*pchanged_states |= (1 << s);
}
}
static void calc_avgs(unsigned long avg[3], int missed_periods,
u64 time, u64 period)
{
unsigned long pct;
/* Fill in zeroes for periods of no activity */
if (missed_periods) {
avg[0] = calc_load_n(avg[0], EXP_10s, 0, missed_periods);
avg[1] = calc_load_n(avg[1], EXP_60s, 0, missed_periods);
avg[2] = calc_load_n(avg[2], EXP_300s, 0, missed_periods);
}
/* Sample the most recent active period */
pct = div_u64(time * 100, period);
pct *= FIXED_1;
avg[0] = calc_load(avg[0], EXP_10s, pct);
avg[1] = calc_load(avg[1], EXP_60s, pct);
avg[2] = calc_load(avg[2], EXP_300s, pct);
}
static void collect_percpu_times(struct psi_group *group,
enum psi_aggregators aggregator,
u32 *pchanged_states)
{
u64 deltas[NR_PSI_STATES - 1] = { 0, };
unsigned long nonidle_total = 0;
u32 changed_states = 0;
int cpu;
int s;
/*
* Collect the per-cpu time buckets and average them into a
* single time sample that is normalized to wallclock time.
*
* For averaging, each CPU is weighted by its non-idle time in
* the sampling period. This eliminates artifacts from uneven
* loading, or even entirely idle CPUs.
*/
for_each_possible_cpu(cpu) {
u32 times[NR_PSI_STATES];
u32 nonidle;
u32 cpu_changed_states;
get_recent_times(group, cpu, aggregator, times,
&cpu_changed_states);
changed_states |= cpu_changed_states;
nonidle = nsecs_to_jiffies(times[PSI_NONIDLE]);
nonidle_total += nonidle;
for (s = 0; s < PSI_NONIDLE; s++)
deltas[s] += (u64)times[s] * nonidle;
}
/*
* Integrate the sample into the running statistics that are
* reported to userspace: the cumulative stall times and the
* decaying averages.
*
* Pressure percentages are sampled at PSI_FREQ. We might be
* called more often when the user polls more frequently than
* that; we might be called less often when there is no task
* activity, thus no data, and clock ticks are sporadic. The
* below handles both.
*/
/* total= */
for (s = 0; s < NR_PSI_STATES - 1; s++)
group->total[aggregator][s] +=
div_u64(deltas[s], max(nonidle_total, 1UL));
if (pchanged_states)
*pchanged_states = changed_states;
}
static u64 update_averages(struct psi_group *group, u64 now)
{
unsigned long missed_periods = 0;
u64 expires, period;
u64 avg_next_update;
int s;
/* avgX= */
expires = group->avg_next_update;
if (now - expires >= psi_period)
missed_periods = div_u64(now - expires, psi_period);
/*
* The periodic clock tick can get delayed for various
* reasons, especially on loaded systems. To avoid clock
* drift, we schedule the clock in fixed psi_period intervals.
* But the deltas we sample out of the per-cpu buckets above
* are based on the actual time elapsing between clock ticks.
*/
avg_next_update = expires + ((1 + missed_periods) * psi_period);
period = now - (group->avg_last_update + (missed_periods * psi_period));
group->avg_last_update = now;
for (s = 0; s < NR_PSI_STATES - 1; s++) {
u32 sample;
sample = group->total[PSI_AVGS][s] - group->avg_total[s];
/*
* Due to the lockless sampling of the time buckets,
* recorded time deltas can slip into the next period,
* which under full pressure can result in samples in
* excess of the period length.
*
* We don't want to report non-sensical pressures in
* excess of 100%, nor do we want to drop such events
* on the floor. Instead we punt any overage into the
* future until pressure subsides. By doing this we
* don't underreport the occurring pressure curve, we
* just report it delayed by one period length.
*
* The error isn't cumulative. As soon as another
* delta slips from a period P to P+1, by definition
* it frees up its time T in P.
*/
if (sample > period)
sample = period;
group->avg_total[s] += sample;
calc_avgs(group->avg[s], missed_periods, sample, period);
}
return avg_next_update;
}
static void psi_avgs_work(struct work_struct *work)
{
struct delayed_work *dwork;
struct psi_group *group;
u32 changed_states;
bool nonidle;
u64 now;
dwork = to_delayed_work(work);
group = container_of(dwork, struct psi_group, avgs_work);
mutex_lock(&group->avgs_lock);
now = sched_clock();
collect_percpu_times(group, PSI_AVGS, &changed_states);
nonidle = changed_states & (1 << PSI_NONIDLE);
/*
* If there is task activity, periodically fold the per-cpu
* times and feed samples into the running averages. If things
* are idle and there is no data to process, stop the clock.
* Once restarted, we'll catch up the running averages in one
* go - see calc_avgs() and missed_periods.
*/
if (now >= group->avg_next_update)
group->avg_next_update = update_averages(group, now);
if (nonidle) {
schedule_delayed_work(dwork, nsecs_to_jiffies(
group->avg_next_update - now) + 1);
}
mutex_unlock(&group->avgs_lock);
}
/* Trigger tracking window manupulations */
static void window_reset(struct psi_window *win, u64 now, u64 value,
u64 prev_growth)
{
win->start_time = now;
win->start_value = value;
win->prev_growth = prev_growth;
}
/*
* PSI growth tracking window update and growth calculation routine.
*
* This approximates a sliding tracking window by interpolating
* partially elapsed windows using historical growth data from the
* previous intervals. This minimizes memory requirements (by not storing
* all the intermediate values in the previous window) and simplifies
* the calculations. It works well because PSI signal changes only in
* positive direction and over relatively small window sizes the growth
* is close to linear.
*/
static u64 window_update(struct psi_window *win, u64 now, u64 value)
{
u64 elapsed;
u64 growth;
elapsed = now - win->start_time;
growth = value - win->start_value;
/*
* After each tracking window passes win->start_value and
* win->start_time get reset and win->prev_growth stores
* the average per-window growth of the previous window.
* win->prev_growth is then used to interpolate additional
* growth from the previous window assuming it was linear.
*/
if (elapsed > win->size)
window_reset(win, now, value, growth);
else {
u32 remaining;
remaining = win->size - elapsed;
growth += div_u64(win->prev_growth * remaining, win->size);
}
return growth;
}
static void init_triggers(struct psi_group *group, u64 now)
{
struct psi_trigger *t;
list_for_each_entry(t, &group->triggers, node)
window_reset(&t->win, now,
group->total[PSI_POLL][t->state], 0);
memcpy(group->polling_total, group->total[PSI_POLL],
sizeof(group->polling_total));
group->polling_next_update = now + group->poll_min_period;
}
static u64 update_triggers(struct psi_group *group, u64 now)
{
struct psi_trigger *t;
bool new_stall = false;
u64 *total = group->total[PSI_POLL];
/*
* On subsequent updates, calculate growth deltas and let
* watchers know when their specified thresholds are exceeded.
*/
list_for_each_entry(t, &group->triggers, node) {
u64 growth;
/* Check for stall activity */
if (group->polling_total[t->state] == total[t->state])
continue;
/*
* Multiple triggers might be looking at the same state,
* remember to update group->polling_total[] once we've
* been through all of them. Also remember to extend the
* polling time if we see new stall activity.
*/
new_stall = true;
/* Calculate growth since last update */
growth = window_update(&t->win, now, total[t->state]);
if (growth < t->threshold)
continue;
/* Limit event signaling to once per window */
if (now < t->last_event_time + t->win.size)
continue;
/* Generate an event */
if (cmpxchg(&t->event, 0, 1) == 0)
wake_up_interruptible(&t->event_wait);
t->last_event_time = now;
}
if (new_stall)
memcpy(group->polling_total, total,
sizeof(group->polling_total));
return now + group->poll_min_period;
}
/*
* Schedule polling if it's not already scheduled. It's safe to call even from
* hotpath because even though kthread_queue_delayed_work takes worker->lock
* spinlock that spinlock is never contended due to poll_scheduled atomic
* preventing such competition.
*/
static void psi_schedule_poll_work(struct psi_group *group, unsigned long delay)
{
struct kthread_worker *kworker;
/* Do not reschedule if already scheduled */
if (atomic_cmpxchg(&group->poll_scheduled, 0, 1) != 0)
return;
rcu_read_lock();
kworker = rcu_dereference(group->poll_kworker);
/*
* kworker might be NULL in case psi_trigger_destroy races with
* psi_task_change (hotpath) which can't use locks
*/
if (likely(kworker))
kthread_queue_delayed_work(kworker, &group->poll_work, delay);
else
atomic_set(&group->poll_scheduled, 0);
rcu_read_unlock();
}
static void psi_poll_work(struct kthread_work *work)
{
struct kthread_delayed_work *dwork;
struct psi_group *group;
u32 changed_states;
u64 now;
dwork = container_of(work, struct kthread_delayed_work, work);
group = container_of(dwork, struct psi_group, poll_work);
atomic_set(&group->poll_scheduled, 0);
mutex_lock(&group->trigger_lock);
now = sched_clock();
collect_percpu_times(group, PSI_POLL, &changed_states);
if (changed_states & group->poll_states) {
/* Initialize trigger windows when entering polling mode */
if (now > group->polling_until)
init_triggers(group, now);
/*
* Keep the monitor active for at least the duration of the
* minimum tracking window as long as monitor states are
* changing.
*/
group->polling_until = now +
group->poll_min_period * UPDATES_PER_WINDOW;
}
if (now > group->polling_until) {
group->polling_next_update = ULLONG_MAX;
goto out;
}
if (now >= group->polling_next_update)
group->polling_next_update = update_triggers(group, now);
psi_schedule_poll_work(group,
nsecs_to_jiffies(group->polling_next_update - now) + 1);
out:
mutex_unlock(&group->trigger_lock);
}
static void record_times(struct psi_group_cpu *groupc, int cpu,
bool memstall_tick)
{
u32 delta;
u64 now;
now = cpu_clock(cpu);
delta = now - groupc->state_start;
groupc->state_start = now;
if (groupc->state_mask & (1 << PSI_IO_SOME)) {
groupc->times[PSI_IO_SOME] += delta;
if (groupc->state_mask & (1 << PSI_IO_FULL))
groupc->times[PSI_IO_FULL] += delta;
}
if (groupc->state_mask & (1 << PSI_MEM_SOME)) {
groupc->times[PSI_MEM_SOME] += delta;
if (groupc->state_mask & (1 << PSI_MEM_FULL))
groupc->times[PSI_MEM_FULL] += delta;
else if (memstall_tick) {
u32 sample;
/*
* Since we care about lost potential, a
* memstall is FULL when there are no other
* working tasks, but also when the CPU is
* actively reclaiming and nothing productive
* could run even if it were runnable.
*
* When the timer tick sees a reclaiming CPU,
* regardless of runnable tasks, sample a FULL
* tick (or less if it hasn't been a full tick
* since the last state change).
*/
sample = min(delta, (u32)jiffies_to_nsecs(1));
groupc->times[PSI_MEM_FULL] += sample;
}
}
if (groupc->state_mask & (1 << PSI_CPU_SOME))
groupc->times[PSI_CPU_SOME] += delta;
if (groupc->state_mask & (1 << PSI_NONIDLE))
groupc->times[PSI_NONIDLE] += delta;
}
static u32 psi_group_change(struct psi_group *group, int cpu,
unsigned int clear, unsigned int set)
{
struct psi_group_cpu *groupc;
unsigned int t, m;
enum psi_states s;
u32 state_mask = 0;
groupc = per_cpu_ptr(group->pcpu, cpu);
/*
* First we assess the aggregate resource states this CPU's
* tasks have been in since the last change, and account any
* SOME and FULL time these may have resulted in.
*
* Then we update the task counts according to the state
* change requested through the @clear and @set bits.
*/
write_seqcount_begin(&groupc->seq);
record_times(groupc, cpu, false);
for (t = 0, m = clear; m; m &= ~(1 << t), t++) {
if (!(m & (1 << t)))
continue;
if (groupc->tasks[t] == 0 && !psi_bug) {
printk_deferred(KERN_ERR "psi: task underflow! cpu=%d t=%d tasks=[%u %u %u] clear=%x set=%x\n",
cpu, t, groupc->tasks[0],
groupc->tasks[1], groupc->tasks[2],
clear, set);
psi_bug = 1;
}
groupc->tasks[t]--;
}
for (t = 0; set; set &= ~(1 << t), t++)
if (set & (1 << t))
groupc->tasks[t]++;
/* Calculate state mask representing active states */
for (s = 0; s < NR_PSI_STATES; s++) {
if (test_state(groupc->tasks, s))
state_mask |= (1 << s);
}
groupc->state_mask = state_mask;
write_seqcount_end(&groupc->seq);
return state_mask;
}
static struct psi_group *iterate_groups(struct task_struct *task, void **iter)
{
#ifdef CONFIG_CGROUPS
struct cgroup *cgroup = NULL;
if (!*iter)
cgroup = task->cgroups->dfl_cgrp;
else if (*iter == &psi_system)
return NULL;
else
cgroup = cgroup_parent(*iter);
if (cgroup && cgroup_parent(cgroup)) {
*iter = cgroup;
return cgroup_psi(cgroup);
}
#else
if (*iter)
return NULL;
#endif
*iter = &psi_system;
return &psi_system;
}
void psi_task_change(struct task_struct *task, int clear, int set)
{
int cpu = task_cpu(task);
struct psi_group *group;
bool wake_clock = true;
void *iter = NULL;
if (!task->pid)
return;
if (((task->psi_flags & set) ||
(task->psi_flags & clear) != clear) &&
!psi_bug) {
printk_deferred(KERN_ERR "psi: inconsistent task state! task=%d:%s cpu=%d psi_flags=%x clear=%x set=%x\n",
task->pid, task->comm, cpu,
task->psi_flags, clear, set);
psi_bug = 1;
}
task->psi_flags &= ~clear;
task->psi_flags |= set;
/*
* Periodic aggregation shuts off if there is a period of no
* task changes, so we wake it back up if necessary. However,
* don't do this if the task change is the aggregation worker
* itself going to sleep, or we'll ping-pong forever.
*/
if (unlikely((clear & TSK_RUNNING) &&
(task->flags & PF_WQ_WORKER) &&
wq_worker_last_func(task) == psi_avgs_work))
wake_clock = false;
while ((group = iterate_groups(task, &iter))) {
u32 state_mask = psi_group_change(group, cpu, clear, set);
if (state_mask & group->poll_states)
psi_schedule_poll_work(group, 1);
if (wake_clock && !delayed_work_pending(&group->avgs_work))
schedule_delayed_work(&group->avgs_work, PSI_FREQ);
}
}
void psi_memstall_tick(struct task_struct *task, int cpu)
{
struct psi_group *group;
void *iter = NULL;
while ((group = iterate_groups(task, &iter))) {
struct psi_group_cpu *groupc;
groupc = per_cpu_ptr(group->pcpu, cpu);
write_seqcount_begin(&groupc->seq);
record_times(groupc, cpu, true);
write_seqcount_end(&groupc->seq);
}
}
/**
* psi_memstall_enter - mark the beginning of a memory stall section
* @flags: flags to handle nested sections
*
* Marks the calling task as being stalled due to a lack of memory,
* such as waiting for a refault or performing reclaim.
*/
void psi_memstall_enter(unsigned long *flags)
{
struct rq_flags rf;
struct rq *rq;
if (static_branch_likely(&psi_disabled))
return;
*flags = current->flags & PF_MEMSTALL;
if (*flags)
return;
/*
* PF_MEMSTALL setting & accounting needs to be atomic wrt
* changes to the task's scheduling state, otherwise we can
* race with CPU migration.
*/
rq = this_rq_lock_irq(&rf);
current->flags |= PF_MEMSTALL;
psi_task_change(current, 0, TSK_MEMSTALL);
rq_unlock_irq(rq, &rf);
}
/**
* psi_memstall_leave - mark the end of an memory stall section
* @flags: flags to handle nested memdelay sections
*
* Marks the calling task as no longer stalled due to lack of memory.
*/
void psi_memstall_leave(unsigned long *flags)
{
struct rq_flags rf;
struct rq *rq;
if (static_branch_likely(&psi_disabled))
return;
if (*flags)
return;
/*
* PF_MEMSTALL clearing & accounting needs to be atomic wrt
* changes to the task's scheduling state, otherwise we could
* race with CPU migration.
*/
rq = this_rq_lock_irq(&rf);
current->flags &= ~PF_MEMSTALL;
psi_task_change(current, TSK_MEMSTALL, 0);
rq_unlock_irq(rq, &rf);
}
#ifdef CONFIG_CGROUPS
int psi_cgroup_alloc(struct cgroup *cgroup)
{
if (static_branch_likely(&psi_disabled))
return 0;
cgroup->psi.pcpu = alloc_percpu(struct psi_group_cpu);
if (!cgroup->psi.pcpu)
return -ENOMEM;
group_init(&cgroup->psi);
return 0;
}
void psi_cgroup_free(struct cgroup *cgroup)
{
if (static_branch_likely(&psi_disabled))
return;
cancel_delayed_work_sync(&cgroup->psi.avgs_work);
free_percpu(cgroup->psi.pcpu);
/* All triggers must be removed by now */
WARN_ONCE(cgroup->psi.poll_states, "psi: trigger leak\n");
}
/**
* cgroup_move_task - move task to a different cgroup
* @task: the task
* @to: the target css_set
*
* Move task to a new cgroup and safely migrate its associated stall
* state between the different groups.
*
* This function acquires the task's rq lock to lock out concurrent
* changes to the task's scheduling state and - in case the task is
* running - concurrent changes to its stall state.
*/
void cgroup_move_task(struct task_struct *task, struct css_set *to)
{
unsigned int task_flags = 0;
struct rq_flags rf;
struct rq *rq;
if (static_branch_likely(&psi_disabled)) {
/*
* Lame to do this here, but the scheduler cannot be locked
* from the outside, so we move cgroups from inside sched/.
*/
rcu_assign_pointer(task->cgroups, to);
return;
}
rq = task_rq_lock(task, &rf);
if (task_on_rq_queued(task))
task_flags = TSK_RUNNING;
else if (task->in_iowait)
task_flags = TSK_IOWAIT;
if (task->flags & PF_MEMSTALL)
task_flags |= TSK_MEMSTALL;
if (task_flags)
psi_task_change(task, task_flags, 0);
/* See comment above */
rcu_assign_pointer(task->cgroups, to);
if (task_flags)
psi_task_change(task, 0, task_flags);
task_rq_unlock(rq, task, &rf);
}
#endif /* CONFIG_CGROUPS */
int psi_show(struct seq_file *m, struct psi_group *group, enum psi_res res)
{
int full;
u64 now;
if (static_branch_likely(&psi_disabled))
return -EOPNOTSUPP;
/* Update averages before reporting them */
mutex_lock(&group->avgs_lock);
now = sched_clock();
collect_percpu_times(group, PSI_AVGS, NULL);
if (now >= group->avg_next_update)
group->avg_next_update = update_averages(group, now);
mutex_unlock(&group->avgs_lock);
for (full = 0; full < 2 - (res == PSI_CPU); full++) {
unsigned long avg[3];
u64 total;
int w;
for (w = 0; w < 3; w++)
avg[w] = group->avg[res * 2 + full][w];
total = div_u64(group->total[PSI_AVGS][res * 2 + full],
NSEC_PER_USEC);
seq_printf(m, "%s avg10=%lu.%02lu avg60=%lu.%02lu avg300=%lu.%02lu total=%llu\n",
full ? "full" : "some",
LOAD_INT(avg[0]), LOAD_FRAC(avg[0]),
LOAD_INT(avg[1]), LOAD_FRAC(avg[1]),
LOAD_INT(avg[2]), LOAD_FRAC(avg[2]),
total);
}
return 0;
}
static int psi_io_show(struct seq_file *m, void *v)
{
return psi_show(m, &psi_system, PSI_IO);
}
static int psi_memory_show(struct seq_file *m, void *v)
{
return psi_show(m, &psi_system, PSI_MEM);
}
static int psi_cpu_show(struct seq_file *m, void *v)
{
return psi_show(m, &psi_system, PSI_CPU);
}
static int psi_io_open(struct inode *inode, struct file *file)
{
return single_open(file, psi_io_show, NULL);
}
static int psi_memory_open(struct inode *inode, struct file *file)
{
return single_open(file, psi_memory_show, NULL);
}
static int psi_cpu_open(struct inode *inode, struct file *file)
{
return single_open(file, psi_cpu_show, NULL);
}
struct psi_trigger *psi_trigger_create(struct psi_group *group,
char *buf, size_t nbytes, enum psi_res res)
{
struct psi_trigger *t;
enum psi_states state;
u32 threshold_us;
u32 window_us;
if (static_branch_likely(&psi_disabled))
return ERR_PTR(-EOPNOTSUPP);
if (sscanf(buf, "some %u %u", &threshold_us, &window_us) == 2)
state = PSI_IO_SOME + res * 2;
else if (sscanf(buf, "full %u %u", &threshold_us, &window_us) == 2)
state = PSI_IO_FULL + res * 2;
else
return ERR_PTR(-EINVAL);
if (state >= PSI_NONIDLE)
return ERR_PTR(-EINVAL);
if (window_us < WINDOW_MIN_US ||
window_us > WINDOW_MAX_US)
return ERR_PTR(-EINVAL);
/* Check threshold */
if (threshold_us == 0 || threshold_us > window_us)
return ERR_PTR(-EINVAL);
t = kmalloc(sizeof(*t), GFP_KERNEL);
if (!t)
return ERR_PTR(-ENOMEM);
t->group = group;
t->state = state;
t->threshold = threshold_us * NSEC_PER_USEC;
t->win.size = window_us * NSEC_PER_USEC;
window_reset(&t->win, 0, 0, 0);
t->event = 0;
t->last_event_time = 0;
init_waitqueue_head(&t->event_wait);
kref_init(&t->refcount);
mutex_lock(&group->trigger_lock);
if (!rcu_access_pointer(group->poll_kworker)) {
struct sched_param param = {
.sched_priority = MAX_RT_PRIO - 1,
};
struct kthread_worker *kworker;
kworker = kthread_create_worker(0, "psimon");
if (IS_ERR(kworker)) {
kfree(t);
mutex_unlock(&group->trigger_lock);
return ERR_CAST(kworker);
}
sched_setscheduler(kworker->task, SCHED_FIFO, &param);
kthread_init_delayed_work(&group->poll_work,
psi_poll_work);
rcu_assign_pointer(group->poll_kworker, kworker);
}
list_add(&t->node, &group->triggers);
group->poll_min_period = min(group->poll_min_period,
div_u64(t->win.size, UPDATES_PER_WINDOW));
group->nr_triggers[t->state]++;
group->poll_states |= (1 << t->state);
mutex_unlock(&group->trigger_lock);
return t;
}
static void psi_trigger_destroy(struct kref *ref)
{
struct psi_trigger *t = container_of(ref, struct psi_trigger, refcount);
struct psi_group *group = t->group;
struct kthread_worker *kworker_to_destroy = NULL;
if (static_branch_likely(&psi_disabled))
return;
/*
* Wakeup waiters to stop polling. Can happen if cgroup is deleted
* from under a polling process.
*/
wake_up_interruptible(&t->event_wait);
mutex_lock(&group->trigger_lock);
if (!list_empty(&t->node)) {
struct psi_trigger *tmp;
u64 period = ULLONG_MAX;
list_del(&t->node);
group->nr_triggers[t->state]--;
if (!group->nr_triggers[t->state])
group->poll_states &= ~(1 << t->state);
/* reset min update period for the remaining triggers */
list_for_each_entry(tmp, &group->triggers, node)
period = min(period, div_u64(tmp->win.size,
UPDATES_PER_WINDOW));
group->poll_min_period = period;
/* Destroy poll_kworker when the last trigger is destroyed */
if (group->poll_states == 0) {
group->polling_until = 0;
kworker_to_destroy = rcu_dereference_protected(
group->poll_kworker,
lockdep_is_held(&group->trigger_lock));
rcu_assign_pointer(group->poll_kworker, NULL);
}
}
mutex_unlock(&group->trigger_lock);
/*
* Wait for both *trigger_ptr from psi_trigger_replace and
* poll_kworker RCUs to complete their read-side critical sections
* before destroying the trigger and optionally the poll_kworker
*/
synchronize_rcu();
/*
* Destroy the kworker after releasing trigger_lock to prevent a
* deadlock while waiting for psi_poll_work to acquire trigger_lock
*/
if (kworker_to_destroy) {
kthread_cancel_delayed_work_sync(&group->poll_work);
kthread_destroy_worker(kworker_to_destroy);
}
kfree(t);
}
void psi_trigger_replace(void **trigger_ptr, struct psi_trigger *new)
{
struct psi_trigger *old = *trigger_ptr;
if (static_branch_likely(&psi_disabled))
return;
rcu_assign_pointer(*trigger_ptr, new);
if (old)
kref_put(&old->refcount, psi_trigger_destroy);
}
__poll_t psi_trigger_poll(void **trigger_ptr,
struct file *file, poll_table *wait)
{
__poll_t ret = DEFAULT_POLLMASK;
struct psi_trigger *t;
if (static_branch_likely(&psi_disabled))
return DEFAULT_POLLMASK | EPOLLERR | EPOLLPRI;
rcu_read_lock();
t = rcu_dereference(*(void __rcu __force **)trigger_ptr);
if (!t) {
rcu_read_unlock();
return DEFAULT_POLLMASK | EPOLLERR | EPOLLPRI;
}
kref_get(&t->refcount);
rcu_read_unlock();
poll_wait(file, &t->event_wait, wait);
if (cmpxchg(&t->event, 1, 0) == 1)
ret |= EPOLLPRI;
kref_put(&t->refcount, psi_trigger_destroy);
return ret;
}
static ssize_t psi_write(struct file *file, const char __user *user_buf,
size_t nbytes, enum psi_res res)
{
char buf[32];
size_t buf_size;
struct seq_file *seq;
struct psi_trigger *new;
if (static_branch_likely(&psi_disabled))
return -EOPNOTSUPP;
if (!nbytes)
return -EINVAL;
buf_size = min(nbytes, (sizeof(buf) - 1));
if (copy_from_user(buf, user_buf, buf_size))
return -EFAULT;
buf[buf_size - 1] = '\0';
new = psi_trigger_create(&psi_system, buf, nbytes, res);
if (IS_ERR(new))
return PTR_ERR(new);
seq = file->private_data;
/* Take seq->lock to protect seq->private from concurrent writes */
mutex_lock(&seq->lock);
psi_trigger_replace(&seq->private, new);
mutex_unlock(&seq->lock);
return nbytes;
}
static ssize_t psi_io_write(struct file *file, const char __user *user_buf,
size_t nbytes, loff_t *ppos)
{
return psi_write(file, user_buf, nbytes, PSI_IO);
}
static ssize_t psi_memory_write(struct file *file, const char __user *user_buf,
size_t nbytes, loff_t *ppos)
{
return psi_write(file, user_buf, nbytes, PSI_MEM);
}
static ssize_t psi_cpu_write(struct file *file, const char __user *user_buf,
size_t nbytes, loff_t *ppos)
{
return psi_write(file, user_buf, nbytes, PSI_CPU);
}
static __poll_t psi_fop_poll(struct file *file, poll_table *wait)
{
struct seq_file *seq = file->private_data;
return psi_trigger_poll(&seq->private, file, wait);
}
static int psi_fop_release(struct inode *inode, struct file *file)
{
struct seq_file *seq = file->private_data;
psi_trigger_replace(&seq->private, NULL);
return single_release(inode, file);
}
static const struct file_operations psi_io_fops = {
.open = psi_io_open,
.read = seq_read,
.llseek = seq_lseek,
.write = psi_io_write,
.poll = psi_fop_poll,
.release = psi_fop_release,
};
static const struct file_operations psi_memory_fops = {
.open = psi_memory_open,
.read = seq_read,
.llseek = seq_lseek,
.write = psi_memory_write,
.poll = psi_fop_poll,
.release = psi_fop_release,
};
static const struct file_operations psi_cpu_fops = {
.open = psi_cpu_open,
.read = seq_read,
.llseek = seq_lseek,
.write = psi_cpu_write,
.poll = psi_fop_poll,
.release = psi_fop_release,
};
static int __init psi_proc_init(void)
{
proc_mkdir("pressure", NULL);
proc_create("pressure/io", 0, NULL, &psi_io_fops);
proc_create("pressure/memory", 0, NULL, &psi_memory_fops);
proc_create("pressure/cpu", 0, NULL, &psi_cpu_fops);
return 0;
}
module_init(psi_proc_init);