[PATCH 2/2] timers: split process wide cpu clocks/timers

From: Peter Zijlstra
Date: Thu Feb 05 2009 - 06:33:58 EST

Change the process wide cpu timers/clocks so that we:

1) don't mess up the kernel with too many threads,
2) don't have a per-cpu allocation for each process,
3) have no impact when not used.

In order to accomplish this we're going to split it into two parts:

- clocks; which can take all the time they want since they run
from user context -- ie. sys_clock_gettime(CLOCK_PROCESS_CPUTIME_ID)

- timers; which need constant time sampling but since they're
explicity used, the user can pay the overhead.

The clock readout will go back to a full sum of the thread group, while the
timers will run of a global 'clock' that only runs when needed, so only
programs that make use of the facility pay the price.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Reviewed-by: Ingo Molnar <mingo@xxxxxxx>
---
include/linux/init_task.h | 11 ++---
include/linux/sched.h | 54 +++++++++++++++-----------
kernel/itimer.c | 4 -
kernel/posix-cpu-timers.c | 95 ++++++++++++++++++++++++++++++++++++++++++++--
kernel/sched_stats.h | 45 ++++++++++++---------
5 files changed, 155 insertions(+), 54 deletions(-)

Index: linux-2.6/include/linux/init_task.h
===================================================================
--- linux-2.6.orig/include/linux/init_task.h
+++ linux-2.6/include/linux/init_task.h
@@ -48,12 +48,11 @@ extern struct fs_struct init_fs;
.posix_timers = LIST_HEAD_INIT(sig.posix_timers), \
.cpu_timers = INIT_CPU_TIMERS(sig.cpu_timers), \
.rlim = INIT_RLIMITS, \
- .cputime = { .totals = { \
- .utime = cputime_zero, \
- .stime = cputime_zero, \
- .sum_exec_runtime = 0, \
- .lock = __SPIN_LOCK_UNLOCKED(sig.cputime.totals.lock), \
- }, }, \
+ .cputimer = { \
+ .cputime = INIT_CPUTIME, \
+ .running = 0, \
+ .lock = __SPIN_LOCK_UNLOCKED(sig.cputimer.lock), \
+ }, \
}

extern struct nsproxy init_nsproxy;
Index: linux-2.6/include/linux/sched.h
===================================================================
--- linux-2.6.orig/include/linux/sched.h
+++ linux-2.6/include/linux/sched.h
@@ -451,7 +451,6 @@ struct pacct_struct {
* @utime: time spent in user mode, in &cputime_t units
* @stime: time spent in kernel mode, in &cputime_t units
* @sum_exec_runtime: total time spent on the CPU, in nanoseconds
- * @lock: lock for fields in this struct
*
* This structure groups together three kinds of CPU time that are
* tracked for threads and thread groups. Most things considering
@@ -462,23 +461,33 @@ struct task_cputime {
cputime_t utime;
cputime_t stime;
unsigned long long sum_exec_runtime;
- spinlock_t lock;
};
/* Alternate field names when used to cache expirations. */
#define prof_exp stime
#define virt_exp utime
#define sched_exp sum_exec_runtime

+#define INIT_CPUTIME \
+ (struct task_cputime) { \
+ .utime = cputime_zero, \
+ .stime = cputime_zero, \
+ .sum_exec_runtime = 0, \
+ }
+
/**
- * struct thread_group_cputime - thread group interval timer counts
- * @totals: thread group interval timers; substructure for
- * uniprocessor kernel, per-cpu for SMP kernel.
+ * struct thread_group_cputimer - thread group interval timer counts
+ * @cputime: thread group interval timers.
+ * @running: non-zero when there are timers running and
+ * @cputime receives updates.
+ * @lock: lock for fields in this struct.
*
* This structure contains the version of task_cputime, above, that is
- * used for thread group CPU clock calculations.
+ * used for thread group CPU timer calculations.
*/
-struct thread_group_cputime {
- struct task_cputime totals;
+struct thread_group_cputimer {
+ struct task_cputime cputime;
+ int running;
+ spinlock_t lock;
};

/*
@@ -527,10 +536,10 @@ struct signal_struct {
cputime_t it_prof_incr, it_virt_incr;

/*
- * Thread group totals for process CPU clocks.
- * See thread_group_cputime(), et al, for details.
+ * Thread group totals for process CPU timers.
+ * See thread_group_cputimer(), et al, for details.
*/
- struct thread_group_cputime cputime;
+ struct thread_group_cputimer cputimer;

/* Earliest-expiration cache. */
struct task_cputime cputime_expires;
@@ -2218,27 +2227,26 @@ static inline int spin_needbreak(spinloc
/*
* Thread group CPU time accounting.
*/
+void thread_group_cputime(struct task_struct *tsk, struct task_cputime *times);

static inline
-void thread_group_cputime(struct task_struct *tsk, struct task_cputime *times)
+void thread_group_cputimer(struct task_struct *tsk, struct task_cputime *times)
{
- struct task_cputime *totals = &tsk->signal->cputime.totals;
+ struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;
unsigned long flags;

- spin_lock_irqsave(&totals->lock, flags);
- *times = *totals;
- spin_unlock_irqrestore(&totals->lock, flags);
+ WARN_ON(!cputimer->running);
+
+ spin_lock_irqsave(&cputimer->lock, flags);
+ *times = cputimer->cputime;
+ spin_unlock_irqrestore(&cputimer->lock, flags);
}

static inline void thread_group_cputime_init(struct signal_struct *sig)
{
- sig->cputime.totals = (struct task_cputime){
- .utime = cputime_zero,
- .stime = cputime_zero,
- .sum_exec_runtime = 0,
- };
-
- spin_lock_init(&sig->cputime.totals.lock);
+ sig->cputimer.cputime = INIT_CPUTIME;
+ spin_lock_init(&sig->cputimer.lock);
+ sig->cputimer.running = 0;
}

static inline void thread_group_cputime_free(struct signal_struct *sig)
Index: linux-2.6/kernel/itimer.c
===================================================================
--- linux-2.6.orig/kernel/itimer.c
+++ linux-2.6/kernel/itimer.c
@@ -62,7 +62,7 @@ int do_getitimer(int which, struct itime
struct task_cputime cputime;
cputime_t utime;

- thread_group_cputime(tsk, &cputime);
+ thread_group_cputimer(tsk, &cputime);
utime = cputime.utime;
if (cputime_le(cval, utime)) { /* about to fire */
cval = jiffies_to_cputime(1);
@@ -82,7 +82,7 @@ int do_getitimer(int which, struct itime
struct task_cputime times;
cputime_t ptime;

- thread_group_cputime(tsk, &times);
+ thread_group_cputimer(tsk, &times);
ptime = cputime_add(times.utime, times.stime);
if (cputime_le(cval, ptime)) { /* about to fire */
cval = jiffies_to_cputime(1);
Index: linux-2.6/kernel/posix-cpu-timers.c
===================================================================
--- linux-2.6.orig/kernel/posix-cpu-timers.c
+++ linux-2.6/kernel/posix-cpu-timers.c
@@ -230,6 +230,37 @@ static int cpu_clock_sample(const clocki
return 0;
}

+void thread_group_cputime(struct task_struct *tsk, struct task_cputime *times)
+{
+ struct sighand_struct *sighand;
+ struct signal_struct *sig;
+ struct task_struct *t;
+
+ *times = INIT_CPUTIME;
+
+ rcu_read_lock();
+ sighand = rcu_dereference(tsk->sighand);
+ if (!sighand)
+ goto out;
+
+ sig = tsk->signal;
+
+ t = tsk;
+ do {
+ times->utime = cputime_add(times->utime, t->utime);
+ times->stime = cputime_add(times->stime, t->stime);
+ times->sum_exec_runtime += t->se.sum_exec_runtime;
+
+ t = next_thread(t);
+ } while (t != tsk);
+
+ times->utime = cputime_add(times->utime, sig->utime);
+ times->stime = cputime_add(times->stime, sig->stime);
+ times->sum_exec_runtime += sig->sum_sched_runtime;
+out:
+ rcu_read_unlock();
+}
+
/*
* Sample a process (thread group) clock for the given group_leader task.
* Must be called with tasklist_lock held for reading.
@@ -476,6 +507,29 @@ static void clear_dead_task(struct k_iti
}

/*
+ * Enable the process wide cpu timer accounting.
+ *
+ * serialized using ->sighand->siglock
+ */
+static void start_process_timers(struct task_struct *tsk)
+{
+ tsk->signal->cputimer.running = 1;
+ barrier();
+}
+
+/*
+ * Release the process wide timer accounting -- timer stops ticking when
+ * nobody cares about it.
+ *
+ * serialized using ->sighand->siglock
+ */
+static void stop_process_timers(struct task_struct *tsk)
+{
+ tsk->signal->cputimer.running = 0;
+ barrier();
+}
+
+/*
* Insert the timer on the appropriate list before any timers that
* expire later. This must be called with the tasklist_lock held
* for reading, and interrupts disabled.
@@ -495,6 +549,9 @@ static void arm_timer(struct k_itimer *t
BUG_ON(!irqs_disabled());
spin_lock(&p->sighand->siglock);

+ if (!CPUCLOCK_PERTHREAD(timer->it_clock))
+ start_process_timers(p);
+
listpos = head;
if (CPUCLOCK_WHICH(timer->it_clock) == CPUCLOCK_SCHED) {
list_for_each_entry(next, head, entry) {
@@ -987,13 +1044,15 @@ static void check_process_timers(struct
sig->rlim[RLIMIT_CPU].rlim_cur == RLIM_INFINITY &&
list_empty(&timers[CPUCLOCK_VIRT]) &&
cputime_eq(sig->it_virt_expires, cputime_zero) &&
- list_empty(&timers[CPUCLOCK_SCHED]))
+ list_empty(&timers[CPUCLOCK_SCHED])) {
+ stop_process_timers(tsk);
return;
+ }

/*
* Collect the current process totals.
*/
- thread_group_cputime(tsk, &cputime);
+ thread_group_cputimer(tsk, &cputime);
utime = cputime.utime;
ptime = cputime_add(utime, cputime.stime);
sum_sched_runtime = cputime.sum_exec_runtime;
@@ -1259,7 +1318,7 @@ static inline int fastpath_timer_check(s
if (!task_cputime_zero(&sig->cputime_expires)) {
struct task_cputime group_sample;

- thread_group_cputime(tsk, &group_sample);
+ thread_group_cputimer(tsk, &group_sample);
if (task_cputime_expired(&group_sample, &sig->cputime_expires))
return 1;
}
@@ -1329,6 +1388,33 @@ void run_posix_cpu_timers(struct task_st
}

/*
+ * Sample a process (thread group) timer for the given group_leader task.
+ * Must be called with tasklist_lock held for reading.
+ */
+static int cpu_timer_sample_group(const clockid_t which_clock,
+ struct task_struct *p,
+ union cpu_time_count *cpu)
+{
+ struct task_cputime cputime;
+
+ thread_group_cputimer(p, &cputime);
+ switch (CPUCLOCK_WHICH(which_clock)) {
+ default:
+ return -EINVAL;
+ case CPUCLOCK_PROF:
+ cpu->cpu = cputime_add(cputime.utime, cputime.stime);
+ break;
+ case CPUCLOCK_VIRT:
+ cpu->cpu = cputime.utime;
+ break;
+ case CPUCLOCK_SCHED:
+ cpu->sched = cputime.sum_exec_runtime + task_delta_exec(p);
+ break;
+ }
+ return 0;
+}
+
+/*
* Set one of the process-wide special case CPU timers.
* The tsk->sighand->siglock must be held by the caller.
* The *newval argument is relative and we update it to be absolute, *oldval
@@ -1341,7 +1427,8 @@ void set_process_cpu_timer(struct task_s
struct list_head *head;

BUG_ON(clock_idx == CPUCLOCK_SCHED);
- cpu_clock_sample_group(clock_idx, tsk, &now);
+ start_process_timers(tsk);
+ cpu_timer_sample_group(clock_idx, tsk, &now);

if (oldval) {
if (!cputime_eq(*oldval, cputime_zero)) {
Index: linux-2.6/kernel/sched_stats.h
===================================================================
--- linux-2.6.orig/kernel/sched_stats.h
+++ linux-2.6/kernel/sched_stats.h
@@ -296,19 +296,21 @@ sched_info_switch(struct task_struct *pr
static inline void account_group_user_time(struct task_struct *tsk,
cputime_t cputime)
{
- struct task_cputime *times;
- struct signal_struct *sig;
+ struct thread_group_cputimer *cputimer;

/* tsk == current, ensure it is safe to use ->signal */
if (unlikely(tsk->exit_state))
return;

- sig = tsk->signal;
- times = &sig->cputime.totals;
+ cputimer = &tsk->signal->cputimer;

- spin_lock(&times->lock);
- times->utime = cputime_add(times->utime, cputime);
- spin_unlock(&times->lock);
+ if (!cputimer->running)
+ return;
+
+ spin_lock(&cputimer->lock);
+ cputimer->cputime.utime =
+ cputime_add(cputimer->cputime.utime, cputime);
+ spin_unlock(&cputimer->lock);
}

/**
@@ -324,19 +326,21 @@ static inline void account_group_user_ti
static inline void account_group_system_time(struct task_struct *tsk,
cputime_t cputime)
{
- struct task_cputime *times;
- struct signal_struct *sig;
+ struct thread_group_cputimer *cputimer;

/* tsk == current, ensure it is safe to use ->signal */
if (unlikely(tsk->exit_state))
return;

- sig = tsk->signal;
- times = &sig->cputime.totals;
+ cputimer = &tsk->signal->cputimer;
+
+ if (!cputimer->running)
+ return;

- spin_lock(&times->lock);
- times->stime = cputime_add(times->stime, cputime);
- spin_unlock(&times->lock);
+ spin_lock(&cputimer->lock);
+ cputimer->cputime.stime =
+ cputime_add(cputimer->cputime.stime, cputime);
+ spin_unlock(&cputimer->lock);
}

/**
@@ -352,7 +356,7 @@ static inline void account_group_system_
static inline void account_group_exec_runtime(struct task_struct *tsk,
unsigned long long ns)
{
- struct task_cputime *times;
+ struct thread_group_cputimer *cputimer;
struct signal_struct *sig;

sig = tsk->signal;
@@ -361,9 +365,12 @@ static inline void account_group_exec_ru
if (unlikely(!sig))
return;

- times = &sig->cputime.totals;
+ cputimer = &sig->cputimer;
+
+ if (!cputimer->running)
+ return;

- spin_lock(&times->lock);
- times->sum_exec_runtime += ns;
- spin_unlock(&times->lock);
+ spin_lock(&cputimer->lock);
+ cputimer->cputime.sum_exec_runtime += ns;
+ spin_unlock(&cputimer->lock);
}

--

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