[patch 43/44] posix-cpu-timers: Utilize timerqueue for storage

Thomas Gleixner
2019-08-19T15:46:36Z

Using a linear O(N) search for timer insertion affects execution time and
Dcache 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.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
include/linux/posix-timers.h | 77 ++++++++++++------
include/linux/timerqueue.h | 10 ++
kernel/time/posix-cpu-timers.c | 174 ++++++++++++++++++++---------------------
3 files changed, 148 insertions(+), 113 deletions(-)

--- a/include/linux/posix-timers.h
+++ b/include/linux/posix-timers.h
@@ -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:
*
@@ -63,6 +57,51 @@ static inline int clockid_to_fd(const cl
}

#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_cputimers - Container for posix CPU timer related data
* @expiries: Earliest-expiration cache array based
@@ -78,17 +117,14 @@ struct posix_cputimers {
u64 expiries[CPUCLOCK_MAX];
unsigned int timers_active;
unsigned int expiry_active;
- struct list_head cpu_timers[CPUCLOCK_MAX];
+ struct timerqueue_head cpu_timers[CPUCLOCK_MAX];
};

static inline void posix_cputimers_init(struct posix_cputimers *pct)
{
memset(&pct->expiries, 0xff, sizeof(pct->expiries));
- pct->timers_active = 0;
- pct->expiry_active = 0;
- INIT_LIST_HEAD(&pct->cpu_timers[0]);
- INIT_LIST_HEAD(&pct->cpu_timers[1]);
- INIT_LIST_HEAD(&pct->cpu_timers[2]);
+ memset(&pct->timers_active, 0x00, sizeof(*pct) -
+ offsetof(struct posix_cputimers, timers_active));
}

static inline void posix_cputimers_group_init(struct posix_cputimers *pct,
@@ -108,18 +144,7 @@ static inline void posix_cputimers_rt_wa
}

/* Init task static initializer */
-#define INIT_CPU_TIMERLISTS(c) { \
- LIST_HEAD_INIT(c.cpu_timers[0]), \
- LIST_HEAD_INIT(c.cpu_timers[1]), \
- LIST_HEAD_INIT(c.cpu_timers[2]), \
-}
-
-#define INIT_CPU_TIMERS(s) \
- .posix_cputimers = { \
- .expiries = { U64_MAX, U64_MAX, U64_MAX }, \
- .cpu_timers = INIT_CPU_TIMERLISTS(s.posix_cputimers), \
- },
-
+#define INIT_CPU_TIMERS(s) .posix_cputimers = { },
#else
struct posix_cputimers { };
#define INIT_CPU_TIMERS(s)
@@ -176,7 +201,7 @@ struct k_itimer {
struct {
struct hrtimer timer;
} real;
- struct cpu_timer_list cpu;
+ struct cpu_timer cpu;
struct {
struct alarm alarmtimer;
} alarm;
--- a/include/linux/timerqueue.h
+++ b/include/linux/timerqueue.h
@@ -43,6 +43,16 @@ static inline void timerqueue_init(struc
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;
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -87,19 +87,19 @@ static inline int validate_clock_permiss
* 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++)
@@ -109,10 +109,11 @@ static void bump_cpu_timer(struct k_itim
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 */
@@ -355,7 +356,7 @@ static int posix_cpu_timer_create(struct
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;
}
@@ -368,10 +369,11 @@ static int posix_cpu_timer_create(struct
*/
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;
@@ -383,15 +385,15 @@ static int posix_cpu_timer_del(struct k_
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);
}
@@ -402,12 +404,12 @@ static int posix_cpu_timer_del(struct k_
return ret;
}

-static void cleanup_timers_list(struct list_head *head)
+static void cleanup_timers_list(struct timerqueue_head *head)
{
- struct cpu_timer_list *timer, *next;
+ struct timerqueue_node *node;

- list_for_each_entry_safe(timer, next, head, entry)
- list_del_init(&timer->entry);
+ while ((node = timerqueue_getnext(head)))
+ timerqueue_del(head, node);
}

/*
@@ -444,12 +446,11 @@ void posix_cpu_timers_exit_group(struct
*/
static void arm_timer(struct k_itimer *timer)
{
- struct cpu_timer_list *const nt = &timer->it.cpu;
int clkidx = CPUCLOCK_WHICH(timer->it_clock);
- u64 *cpuexp, newexp = timer->it.cpu.expires;
- struct task_struct *p = timer->it.cpu.task;
- struct list_head *head, *listpos;
- struct cpu_timer_list *next;
+ struct cpu_timer *ctmr = &timer->it.cpu;
+ u64 *cpuexp, newexp = cpu_timer_getexpires(ctmr);
+ struct task_struct *p = ctmr->task;
+ struct timerqueue_head *head;

if (CPUCLOCK_PERTHREAD(timer->it_clock)) {
head = p->posix_cputimers.cpu_timers + clkidx;
@@ -459,15 +460,7 @@ static void arm_timer(struct k_itimer *t
cpuexp = p->signal->posix_cputimers.expiries + clkidx;
}

- listpos = head;
- 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(head, ctmr))
return;

/*
@@ -490,24 +483,26 @@ static void arm_timer(struct k_itimer *t
*/
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
@@ -531,10 +526,11 @@ static int posix_cpu_timer_set(struct k_
{
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;
@@ -554,22 +550,21 @@ static int posix_cpu_timer_set(struct k_
* 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
@@ -590,18 +585,16 @@ static int posix_cpu_timer_set(struct k_
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;
@@ -630,7 +623,7 @@ static int posix_cpu_timer_set(struct k_
* 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);
}
@@ -672,8 +665,9 @@ static int posix_cpu_timer_set(struct k_
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;
@@ -683,7 +677,7 @@ static void posix_cpu_timer_get(struct k
*/
itp->it_interval = ktime_to_timespec64(timer->it_interval);

- if (!timer->it.cpu.expires)
+ if (!expires)
return;

/*
@@ -705,9 +699,9 @@ static void posix_cpu_timer_get(struct k
/*
* 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);
@@ -715,8 +709,8 @@ static void posix_cpu_timer_get(struct k
}
}

- 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
@@ -727,23 +721,27 @@ static void posix_cpu_timer_get(struct k
}
}

-static unsigned long long
-check_timers_list(struct list_head *timers,
- struct list_head *firing,
- unsigned long long curr)
-{
- int maxfire = 20;
-
- while (!list_empty(timers)) {
- struct cpu_timer_list *t;
+#define MAX_COLLECTED 20

- t = list_first_entry(timers, struct cpu_timer_list, entry);
-
- if (!--maxfire || curr < t->expires)
- return t->expires;
+static u64 collect_timerqueue(struct timerqueue_head *head,
+ struct list_head *firing, u64 now)
+{
+ struct timerqueue_node *next;
+ int i = 0;

- t->firing = 1;
- list_move_tail(&t->entry, firing);
+ while ((next = timerqueue_getnext(head))) {
+ struct cpu_timer *ctmr;
+ u64 expires;
+
+ 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;
+
+ ctmr->firing = 1;
+ cpu_timer_dequeue(ctmr);
+ list_add_tail(&ctmr->elist, firing);
}

return U64_MAX;
@@ -752,12 +750,12 @@ check_timers_list(struct list_head *time
static void collect_posix_cputimers(struct posix_cputimers *pct,
u64 *samples, struct list_head *firing)
{
- struct list_head *timers = pct->cpu_timers;
+ struct timerqueue_head *timers = pct->cpu_timers;
u64 *expiries = pct->expiries;
int i;

for (i = 0; i < CPUCLOCK_MAX; i++, timers++)
- expiries[i] = check_timers_list(timers, firing, samples[i]);
+ expiries[i] = collect_timerqueue(timers, firing, samples[i]);
}

static inline void check_dl_overrun(struct task_struct *tsk)
@@ -937,7 +935,8 @@ static void check_process_timers(struct
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;
@@ -969,7 +968,7 @@ static void posix_cpu_timer_rearm(struct
* 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 */
@@ -1127,11 +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;
/*
@@ -1206,6 +1205,7 @@ static int do_cpu_nanosleep(const clocki
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;
@@ -1221,7 +1221,7 @@ static int do_cpu_nanosleep(const clocki
}

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.
@@ -1243,7 +1243,7 @@ static int do_cpu_nanosleep(const clocki
/*
* 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) {
/*