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posix-cpu-timers: Utilize timerqueue for storage 

Using a linear O(N) search for timer insertion affects execution time and
D-cache footprint badly with a larger number of timers.

Switch the storage to a timerqueue which is already used for hrtimers and
alarmtimers. It does not affect the size of struct k_itimer as it.alarm is
still larger.

The extra list head for the expiry list will go away later once the expiry
is moved into task work context.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lkml.kernel.org/r/alpine.DEB.2.21.1908272129220.1939@nanos.tec.linutronix.de
This commit is contained in:
Thomas Gleixner 2019-08-27 21:31:02 +02:00
parent 244d49e306
commit 60bda037f1
3 changed files with 152 additions and 106 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

65
include/linux/posix-timers.h
View File

@ -5,17 +5,11 @@
#include <linux/spinlock.h>
#include <linux/list.h>
#include <linux/alarmtimer.h>
#include <linux/timerqueue.h>
struct kernel_siginfo;
struct task_struct;
struct cpu_timer_list {
struct list_head entry;
u64 expires;
struct task_struct *task;
int firing;
};
/*
* Bit fields within a clockid:
*
@ -64,14 +58,58 @@ static inline int clockid_to_fd(const clockid_t clk)
#ifdef CONFIG_POSIX_TIMERS
/**
* cpu_timer - Posix CPU timer representation for k_itimer
* @node: timerqueue node to queue in the task/sig
* @head: timerqueue head on which this timer is queued
* @task: Pointer to target task
* @elist: List head for the expiry list
* @firing: Timer is currently firing
*/
struct cpu_timer {
struct timerqueue_node node;
struct timerqueue_head *head;
struct task_struct *task;
struct list_head elist;
int firing;
};
static inline bool cpu_timer_requeue(struct cpu_timer *ctmr)
{
return timerqueue_add(ctmr->head, &ctmr->node);
}
static inline bool cpu_timer_enqueue(struct timerqueue_head *head,
struct cpu_timer *ctmr)
{
ctmr->head = head;
return timerqueue_add(head, &ctmr->node);
}
static inline void cpu_timer_dequeue(struct cpu_timer *ctmr)
{
if (!RB_EMPTY_NODE(&ctmr->node.node))
timerqueue_del(ctmr->head, &ctmr->node);
}
static inline u64 cpu_timer_getexpires(struct cpu_timer *ctmr)
{
return ctmr->node.expires;
}
static inline void cpu_timer_setexpires(struct cpu_timer *ctmr, u64 exp)
{
ctmr->node.expires = exp;
}
/**
* posix_cputimer_base - Container per posix CPU clock
* @nextevt: Earliest-expiration cache
* @cpu_timers: List heads to queue posix CPU timers
* @tqhead: timerqueue head for cpu_timers
*/
struct posix_cputimer_base {
u64 nextevt;
struct list_head cpu_timers;
struct timerqueue_head tqhead;
};
/**
@ -92,14 +130,10 @@ struct posix_cputimers {
static inline void posix_cputimers_init(struct posix_cputimers *pct)
{
pct->timers_active = 0;
pct->expiry_active = 0;
memset(pct, 0, sizeof(*pct));
pct->bases[0].nextevt = U64_MAX;
pct->bases[1].nextevt = U64_MAX;
pct->bases[2].nextevt = U64_MAX;
INIT_LIST_HEAD(&pct->bases[0].cpu_timers);
INIT_LIST_HEAD(&pct->bases[1].cpu_timers);
INIT_LIST_HEAD(&pct->bases[2].cpu_timers);
}
void posix_cputimers_group_init(struct posix_cputimers *pct, u64 cpu_limit);
@ -113,7 +147,6 @@ static inline void posix_cputimers_rt_watchdog(struct posix_cputimers *pct,
/* Init task static initializer */
#define INIT_CPU_TIMERBASE(b) { \
.nextevt = U64_MAX, \
.cpu_timers = LIST_HEAD_INIT(b.cpu_timers), \
}
#define INIT_CPU_TIMERBASES(b) { \
@ -182,7 +215,7 @@ struct k_itimer {
struct {
struct hrtimer timer;
} real;
struct cpu_timer_list cpu;
struct cpu_timer cpu;
struct {
struct alarm alarmtimer;
} alarm;

10
include/linux/timerqueue.h
View File

@ -43,6 +43,16 @@ static inline void timerqueue_init(struct timerqueue_node *node)
RB_CLEAR_NODE(&node->node);
}
static inline bool timerqueue_node_queued(struct timerqueue_node *node)
{
return !RB_EMPTY_NODE(&node->node);
}
static inline bool timerqueue_node_expires(struct timerqueue_node *node)
{
return node->expires;
}
static inline void timerqueue_init_head(struct timerqueue_head *head)
{
head->rb_root = RB_ROOT_CACHED;

183
kernel/time/posix-cpu-timers.c
View File

@ -96,19 +96,19 @@ static inline int validate_clock_permissions(const clockid_t clock)
* Update expiry time from increment, and increase overrun count,
* given the current clock sample.
*/
static void bump_cpu_timer(struct k_itimer *timer, u64 now)
static u64 bump_cpu_timer(struct k_itimer *timer, u64 now)
{
u64 delta, incr, expires = timer->it.cpu.node.expires;
int i;
u64 delta, incr;
if (!timer->it_interval)
return;
return expires;
if (now < timer->it.cpu.expires)
return;
if (now < expires)
return expires;
incr = timer->it_interval;
delta = now + incr - timer->it.cpu.expires;
delta = now + incr - expires;
/* Don't use (incr*2 < delta), incr*2 might overflow. */
for (i = 0; incr < delta - incr; i++)
@ -118,10 +118,11 @@ static void bump_cpu_timer(struct k_itimer *timer, u64 now)
if (delta < incr)
continue;
timer->it.cpu.expires += incr;
timer->it.cpu.node.expires += incr;
timer->it_overrun += 1LL << i;
delta -= incr;
}
return timer->it.cpu.node.expires;
}
/* Check whether all cache entries contain U64_MAX, i.e. eternal expiry time */
@ -365,7 +366,7 @@ static int posix_cpu_timer_create(struct k_itimer *new_timer)
return -EINVAL;
new_timer->kclock = &clock_posix_cpu;
INIT_LIST_HEAD(&new_timer->it.cpu.entry);
timerqueue_init(&new_timer->it.cpu.node);
new_timer->it.cpu.task = p;
return 0;
}
@ -378,10 +379,11 @@ static int posix_cpu_timer_create(struct k_itimer *new_timer)
*/
static int posix_cpu_timer_del(struct k_itimer *timer)
{
int ret = 0;
unsigned long flags;
struct cpu_timer *ctmr = &timer->it.cpu;
struct task_struct *p = ctmr->task;
struct sighand_struct *sighand;
struct task_struct *p = timer->it.cpu.task;
unsigned long flags;
int ret = 0;
if (WARN_ON_ONCE(!p))
return -EINVAL;
@ -393,15 +395,15 @@ static int posix_cpu_timer_del(struct k_itimer *timer)
sighand = lock_task_sighand(p, &flags);
if (unlikely(sighand == NULL)) {
/*
* We raced with the reaping of the task.
* The deletion should have cleared us off the list.
* This raced with the reaping of the task. The exit cleanup
* should have removed this timer from the timer queue.
*/
WARN_ON_ONCE(!list_empty(&timer->it.cpu.entry));
WARN_ON_ONCE(ctmr->head || timerqueue_node_queued(&ctmr->node));
} else {
if (timer->it.cpu.firing)
ret = TIMER_RETRY;
else
list_del(&timer->it.cpu.entry);
cpu_timer_dequeue(ctmr);
unlock_task_sighand(p, &flags);
}
@ -412,12 +414,16 @@ static int posix_cpu_timer_del(struct k_itimer *timer)
return ret;
}
static void cleanup_timers_list(struct list_head *head)
static void cleanup_timerqueue(struct timerqueue_head *head)
{
struct cpu_timer_list *timer, *next;
struct timerqueue_node *node;
struct cpu_timer *ctmr;
list_for_each_entry_safe(timer, next, head, entry)
list_del_init(&timer->entry);
while ((node = timerqueue_getnext(head))) {
timerqueue_del(head, node);
ctmr = container_of(node, struct cpu_timer, node);
ctmr->head = NULL;
}
}
/*
@ -429,9 +435,9 @@ static void cleanup_timers_list(struct list_head *head)
*/
static void cleanup_timers(struct posix_cputimers *pct)
{
cleanup_timers_list(&pct->bases[CPUCLOCK_PROF].cpu_timers);
cleanup_timers_list(&pct->bases[CPUCLOCK_VIRT].cpu_timers);
cleanup_timers_list(&pct->bases[CPUCLOCK_SCHED].cpu_timers);
cleanup_timerqueue(&pct->bases[CPUCLOCK_PROF].tqhead);
cleanup_timerqueue(&pct->bases[CPUCLOCK_VIRT].tqhead);
cleanup_timerqueue(&pct->bases[CPUCLOCK_SCHED].tqhead);
}
/*
@ -454,28 +460,18 @@ void posix_cpu_timers_exit_group(struct task_struct *tsk)
*/
static void arm_timer(struct k_itimer *timer)
{
struct cpu_timer_list *const nt = &timer->it.cpu;
int clkidx = CPUCLOCK_WHICH(timer->it_clock);
struct task_struct *p = timer->it.cpu.task;
u64 newexp = timer->it.cpu.expires;
struct cpu_timer *ctmr = &timer->it.cpu;
u64 newexp = cpu_timer_getexpires(ctmr);
struct task_struct *p = ctmr->task;
struct posix_cputimer_base *base;
struct list_head *head, *listpos;
struct cpu_timer_list *next;
if (CPUCLOCK_PERTHREAD(timer->it_clock))
base = p->posix_cputimers.bases + clkidx;
else
base = p->signal->posix_cputimers.bases + clkidx;
listpos = head = &base->cpu_timers;
list_for_each_entry(next,head, entry) {
if (nt->expires < next->expires)
break;
listpos = &next->entry;
}
list_add(&nt->entry, listpos);
if (listpos != head)
if (!cpu_timer_enqueue(&base->tqhead, ctmr))
return;
/*
@ -498,24 +494,26 @@ static void arm_timer(struct k_itimer *timer)
*/
static void cpu_timer_fire(struct k_itimer *timer)
{
struct cpu_timer *ctmr = &timer->it.cpu;
if ((timer->it_sigev_notify & ~SIGEV_THREAD_ID) == SIGEV_NONE) {
/*
* User don't want any signal.
*/
timer->it.cpu.expires = 0;
cpu_timer_setexpires(ctmr, 0);
} else if (unlikely(timer->sigq == NULL)) {
/*
* This a special case for clock_nanosleep,
* not a normal timer from sys_timer_create.
*/
wake_up_process(timer->it_process);
timer->it.cpu.expires = 0;
cpu_timer_setexpires(ctmr, 0);
} else if (!timer->it_interval) {
/*
* One-shot timer. Clear it as soon as it's fired.
*/
posix_timer_event(timer, 0);
timer->it.cpu.expires = 0;
cpu_timer_setexpires(ctmr, 0);
} else if (posix_timer_event(timer, ++timer->it_requeue_pending)) {
/*
* The signal did not get queued because the signal
@ -539,10 +537,11 @@ static int posix_cpu_timer_set(struct k_itimer *timer, int timer_flags,
{
clockid_t clkid = CPUCLOCK_WHICH(timer->it_clock);
u64 old_expires, new_expires, old_incr, val;
struct task_struct *p = timer->it.cpu.task;
struct cpu_timer *ctmr = &timer->it.cpu;
struct task_struct *p = ctmr->task;
struct sighand_struct *sighand;
unsigned long flags;
int ret;
int ret = 0;
if (WARN_ON_ONCE(!p))
return -EINVAL;
@ -562,22 +561,21 @@ static int posix_cpu_timer_set(struct k_itimer *timer, int timer_flags,
* If p has just been reaped, we can no
* longer get any information about it at all.
*/
if (unlikely(sighand == NULL)) {
if (unlikely(sighand == NULL))
return -ESRCH;
}
/*
* Disarm any old timer after extracting its expiry time.
*/
ret = 0;
old_incr = timer->it_interval;
old_expires = timer->it.cpu.expires;
old_expires = cpu_timer_getexpires(ctmr);
if (unlikely(timer->it.cpu.firing)) {
timer->it.cpu.firing = -1;
ret = TIMER_RETRY;
} else
list_del_init(&timer->it.cpu.entry);
} else {
cpu_timer_dequeue(ctmr);
}
/*
* We need to sample the current value to convert the new
@ -598,18 +596,16 @@ static int posix_cpu_timer_set(struct k_itimer *timer, int timer_flags,
old->it_value.tv_nsec = 0;
} else {
/*
* Update the timer in case it has
* overrun already. If it has,
* we'll report it as having overrun
* and with the next reloaded timer
* already ticking, though we are
* swallowing that pending
* notification here to install the
* new setting.
* Update the timer in case it has overrun already.
* If it has, we'll report it as having overrun and
* with the next reloaded timer already ticking,
* though we are swallowing that pending
* notification here to install the new setting.
*/
bump_cpu_timer(timer, val);
if (val < timer->it.cpu.expires) {
old_expires = timer->it.cpu.expires - val;
u64 exp = bump_cpu_timer(timer, val);
if (val < exp) {
old_expires = exp - val;
old->it_value = ns_to_timespec64(old_expires);
} else {
old->it_value.tv_nsec = 1;
@ -638,7 +634,7 @@ static int posix_cpu_timer_set(struct k_itimer *timer, int timer_flags,
* For a timer with no notification action, we don't actually
* arm the timer (we'll just fake it for timer_gettime).
*/
timer->it.cpu.expires = new_expires;
cpu_timer_setexpires(ctmr, new_expires);
if (new_expires != 0 && val < new_expires) {
arm_timer(timer);
}
@ -680,8 +676,9 @@ static int posix_cpu_timer_set(struct k_itimer *timer, int timer_flags,
static void posix_cpu_timer_get(struct k_itimer *timer, struct itimerspec64 *itp)
{
clockid_t clkid = CPUCLOCK_WHICH(timer->it_clock);
struct task_struct *p = timer->it.cpu.task;
u64 now;
struct cpu_timer *ctmr = &timer->it.cpu;
u64 now, expires = cpu_timer_getexpires(ctmr);
struct task_struct *p = ctmr->task;
if (WARN_ON_ONCE(!p))
return;
@ -691,7 +688,7 @@ static void posix_cpu_timer_get(struct k_itimer *timer, struct itimerspec64 *itp
*/
itp->it_interval = ktime_to_timespec64(timer->it_interval);
if (!timer->it.cpu.expires)
if (!expires)
return;
/*
@ -713,9 +710,9 @@ static void posix_cpu_timer_get(struct k_itimer *timer, struct itimerspec64 *itp
/*
* The process has been reaped.
* We can't even collect a sample any more.
* Call the timer disarmed, nothing else to do.
* Disarm the timer, nothing else to do.
*/
timer->it.cpu.expires = 0;
cpu_timer_setexpires(ctmr, 0);
return;
} else {
now = cpu_clock_sample_group(clkid, p, false);
@ -723,8 +720,8 @@ static void posix_cpu_timer_get(struct k_itimer *timer, struct itimerspec64 *itp
}
}
if (now < timer->it.cpu.expires) {
itp->it_value = ns_to_timespec64(timer->it.cpu.expires - now);
if (now < expires) {
itp->it_value = ns_to_timespec64(expires - now);
} else {
/*
* The timer should have expired already, but the firing
@ -735,37 +732,41 @@ static void posix_cpu_timer_get(struct k_itimer *timer, struct itimerspec64 *itp
}
}
static unsigned long long
check_timers_list(struct list_head *timers,
struct list_head *firing,
unsigned long long curr)
#define MAX_COLLECTED 20
static u64 collect_timerqueue(struct timerqueue_head *head,
struct list_head *firing, u64 now)
{
int maxfire = 20;
struct timerqueue_node *next;
int i = 0;
while (!list_empty(timers)) {
struct cpu_timer_list *t;
while ((next = timerqueue_getnext(head))) {
struct cpu_timer *ctmr;
u64 expires;
t = list_first_entry(timers, struct cpu_timer_list, entry);
ctmr = container_of(next, struct cpu_timer, node);
expires = cpu_timer_getexpires(ctmr);
/* Limit the number of timers to expire at once */
if (++i == MAX_COLLECTED || now < expires)
return expires;
if (!--maxfire || curr < t->expires)
return t->expires;
t->firing = 1;
list_move_tail(&t->entry, firing);
ctmr->firing = 1;
cpu_timer_dequeue(ctmr);
list_add_tail(&ctmr->elist, firing);
}
return U64_MAX;
}
static void collect_posix_cputimers(struct posix_cputimers *pct,
u64 *samples, struct list_head *firing)
static void collect_posix_cputimers(struct posix_cputimers *pct, u64 *samples,
struct list_head *firing)
{
struct posix_cputimer_base *base = pct->bases;
int i;
for (i = 0; i < CPUCLOCK_MAX; i++, base++) {
base->nextevt = check_timers_list(&base->cpu_timers, firing,
samples[i]);
base->nextevt = collect_timerqueue(&base->tqhead, firing,
samples[i]);
}
}
@ -948,7 +949,8 @@ static void check_process_timers(struct task_struct *tsk,
static void posix_cpu_timer_rearm(struct k_itimer *timer)
{
clockid_t clkid = CPUCLOCK_WHICH(timer->it_clock);
struct task_struct *p = timer->it.cpu.task;
struct cpu_timer *ctmr = &timer->it.cpu;
struct task_struct *p = ctmr->task;
struct sighand_struct *sighand;
unsigned long flags;
u64 now;
@ -980,7 +982,7 @@ static void posix_cpu_timer_rearm(struct k_itimer *timer)
* The process has been reaped.
* We can't even collect a sample any more.
*/
timer->it.cpu.expires = 0;
cpu_timer_setexpires(ctmr, 0);
return;
} else if (unlikely(p->exit_state) && thread_group_empty(p)) {
/* If the process is dying, no need to rearm */
@ -1124,11 +1126,11 @@ void run_posix_cpu_timers(void)
* each timer's lock before clearing its firing flag, so no
* timer call will interfere.
*/
list_for_each_entry_safe(timer, next, &firing, it.cpu.entry) {
list_for_each_entry_safe(timer, next, &firing, it.cpu.elist) {
int cpu_firing;
spin_lock(&timer->it_lock);
list_del_init(&timer->it.cpu.entry);
list_del_init(&timer->it.cpu.elist);
cpu_firing = timer->it.cpu.firing;
timer->it.cpu.firing = 0;
/*
@ -1204,6 +1206,7 @@ static int do_cpu_nanosleep(const clockid_t which_clock, int flags,
timer.it_overrun = -1;
error = posix_cpu_timer_create(&timer);
timer.it_process = current;
if (!error) {
static struct itimerspec64 zero_it;
struct restart_block *restart;
@ -1219,7 +1222,7 @@ static int do_cpu_nanosleep(const clockid_t which_clock, int flags,
}
while (!signal_pending(current)) {
if (timer.it.cpu.expires == 0) {
if (!cpu_timer_getexpires(&timer.it.cpu)) {
/*
* Our timer fired and was reset, below
* deletion can not fail.
@ -1241,7 +1244,7 @@ static int do_cpu_nanosleep(const clockid_t which_clock, int flags,
/*
* We were interrupted by a signal.
*/
expires = timer.it.cpu.expires;
expires = cpu_timer_getexpires(&timer.it.cpu);
error = posix_cpu_timer_set(&timer, 0, &zero_it, &it);
if (!error) {
/*