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itimers: remove the per-cpu-ish-ness
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Either we bounce once cacheline per cpu per tick, yielding n^2 bounces
or we just bounce a single..

Also, using per-cpu allocations for the thread-groups complicates the
per-cpu allocator in that its currently aimed to be a fixed sized
allocator and the only possible extention to that would be vmap based,
which is seriously constrained on 32 bit archs.

So making the per-cpu memory requirement depend on the number of
processes is an issue.

Lastly, it didn't deal with cpu-hotplug, although admittedly that might
be fixable.

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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Peter Zijlstra authored and Ingo Molnar committed Jan 7, 2009
1 parent ede6f5a commit 490dea4
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Showing 5 changed files with 46 additions and 107 deletions.
6 changes: 6 additions & 0 deletions include/linux/init_task.h
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Original file line number Diff line number Diff line change
Expand Up @@ -48,6 +48,12 @@ 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), \
}, }, \
}

extern struct nsproxy init_nsproxy;
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29 changes: 18 additions & 11 deletions include/linux/sched.h
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Original file line number Diff line number Diff line change
Expand Up @@ -450,6 +450,7 @@ 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
Expand All @@ -465,7 +466,7 @@ struct task_cputime {
* used for thread group CPU clock calculations.
*/
struct thread_group_cputime {
struct task_cputime *totals;
struct task_cputime totals;
};

/*
Expand Down Expand Up @@ -2180,24 +2181,30 @@ static inline int spin_needbreak(spinlock_t *lock)
* Thread group CPU time accounting.
*/

extern int thread_group_cputime_alloc(struct task_struct *);
extern void thread_group_cputime(struct task_struct *, struct task_cputime *);

static inline void thread_group_cputime_init(struct signal_struct *sig)
static inline
void thread_group_cputime(struct task_struct *tsk, struct task_cputime *times)
{
sig->cputime.totals = NULL;
struct task_cputime *totals = &tsk->signal->cputime.totals;
unsigned long flags;

spin_lock_irqsave(&totals->lock, flags);
*times = *totals;
spin_unlock_irqrestore(&totals->lock, flags);
}

static inline int thread_group_cputime_clone_thread(struct task_struct *curr)
static inline void thread_group_cputime_init(struct signal_struct *sig)
{
if (curr->signal->cputime.totals)
return 0;
return thread_group_cputime_alloc(curr);
sig->cputime.totals = (struct task_cputime){
.utime = cputime_zero,
.stime = cputime_zero,
.sum_exec_runtime = 0,
};

spin_lock_init(&sig->cputime.totals.lock);
}

static inline void thread_group_cputime_free(struct signal_struct *sig)
{
free_percpu(sig->cputime.totals);
}

/*
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15 changes: 7 additions & 8 deletions kernel/fork.c
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Original file line number Diff line number Diff line change
Expand Up @@ -820,14 +820,15 @@ static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
int ret;

if (clone_flags & CLONE_THREAD) {
ret = thread_group_cputime_clone_thread(current);
if (likely(!ret)) {
atomic_inc(&current->signal->count);
atomic_inc(&current->signal->live);
}
return ret;
atomic_inc(&current->signal->count);
atomic_inc(&current->signal->live);
return 0;
}
sig = kmem_cache_alloc(signal_cachep, GFP_KERNEL);

if (sig)
posix_cpu_timers_init_group(sig);

tsk->signal = sig;
if (!sig)
return -ENOMEM;
Expand Down Expand Up @@ -864,8 +865,6 @@ static int copy_signal(unsigned long clone_flags, struct task_struct *tsk)
memcpy(sig->rlim, current->signal->rlim, sizeof sig->rlim);
task_unlock(current->group_leader);

posix_cpu_timers_init_group(sig);

acct_init_pacct(&sig->pacct);

tty_audit_fork(sig);
Expand Down
70 changes: 0 additions & 70 deletions kernel/posix-cpu-timers.c
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Original file line number Diff line number Diff line change
Expand Up @@ -9,76 +9,6 @@
#include <asm/uaccess.h>
#include <linux/kernel_stat.h>

/*
* Allocate the thread_group_cputime structure appropriately and fill in the
* current values of the fields. Called from copy_signal() via
* thread_group_cputime_clone_thread() when adding a second or subsequent
* thread to a thread group. Assumes interrupts are enabled when called.
*/
int thread_group_cputime_alloc(struct task_struct *tsk)
{
struct signal_struct *sig = tsk->signal;
struct task_cputime *cputime;

/*
* If we have multiple threads and we don't already have a
* per-CPU task_cputime struct (checked in the caller), allocate
* one and fill it in with the times accumulated so far. We may
* race with another thread so recheck after we pick up the sighand
* lock.
*/
cputime = alloc_percpu(struct task_cputime);
if (cputime == NULL)
return -ENOMEM;
spin_lock_irq(&tsk->sighand->siglock);
if (sig->cputime.totals) {
spin_unlock_irq(&tsk->sighand->siglock);
free_percpu(cputime);
return 0;
}
sig->cputime.totals = cputime;
cputime = per_cpu_ptr(sig->cputime.totals, smp_processor_id());
cputime->utime = tsk->utime;
cputime->stime = tsk->stime;
cputime->sum_exec_runtime = tsk->se.sum_exec_runtime;
spin_unlock_irq(&tsk->sighand->siglock);
return 0;
}

/**
* thread_group_cputime - Sum the thread group time fields across all CPUs.
*
* @tsk: The task we use to identify the thread group.
* @times: task_cputime structure in which we return the summed fields.
*
* Walk the list of CPUs to sum the per-CPU time fields in the thread group
* time structure.
*/
void thread_group_cputime(
struct task_struct *tsk,
struct task_cputime *times)
{
struct task_cputime *totals, *tot;
int i;

totals = tsk->signal->cputime.totals;
if (!totals) {
times->utime = tsk->utime;
times->stime = tsk->stime;
times->sum_exec_runtime = tsk->se.sum_exec_runtime;
return;
}

times->stime = times->utime = cputime_zero;
times->sum_exec_runtime = 0;
for_each_possible_cpu(i) {
tot = per_cpu_ptr(totals, i);
times->utime = cputime_add(times->utime, tot->utime);
times->stime = cputime_add(times->stime, tot->stime);
times->sum_exec_runtime += tot->sum_exec_runtime;
}
}

/*
* Called after updating RLIMIT_CPU to set timer expiration if necessary.
*/
Expand Down
33 changes: 15 additions & 18 deletions kernel/sched_stats.h
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Original file line number Diff line number Diff line change
Expand Up @@ -296,20 +296,19 @@ sched_info_switch(struct task_struct *prev, struct task_struct *next)
static inline void account_group_user_time(struct task_struct *tsk,
cputime_t cputime)
{
struct task_cputime *times;
struct signal_struct *sig;

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

sig = tsk->signal;
if (sig->cputime.totals) {
struct task_cputime *times;
times = &sig->cputime.totals;

times = per_cpu_ptr(sig->cputime.totals, get_cpu());
times->utime = cputime_add(times->utime, cputime);
put_cpu_no_resched();
}
spin_lock(&times->lock);
times->utime = cputime_add(times->utime, cputime);
spin_unlock(&times->lock);
}

/**
Expand All @@ -325,20 +324,19 @@ static inline void account_group_user_time(struct task_struct *tsk,
static inline void account_group_system_time(struct task_struct *tsk,
cputime_t cputime)
{
struct task_cputime *times;
struct signal_struct *sig;

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

sig = tsk->signal;
if (sig->cputime.totals) {
struct task_cputime *times;
times = &sig->cputime.totals;

times = per_cpu_ptr(sig->cputime.totals, get_cpu());
times->stime = cputime_add(times->stime, cputime);
put_cpu_no_resched();
}
spin_lock(&times->lock);
times->stime = cputime_add(times->stime, cputime);
spin_unlock(&times->lock);
}

/**
Expand All @@ -354,6 +352,7 @@ static inline void account_group_system_time(struct task_struct *tsk,
static inline void account_group_exec_runtime(struct task_struct *tsk,
unsigned long long ns)
{
struct task_cputime *times;
struct signal_struct *sig;

sig = tsk->signal;
Expand All @@ -362,11 +361,9 @@ static inline void account_group_exec_runtime(struct task_struct *tsk,
if (unlikely(!sig))
return;

if (sig->cputime.totals) {
struct task_cputime *times;
times = &sig->cputime.totals;

times = per_cpu_ptr(sig->cputime.totals, get_cpu());
times->sum_exec_runtime += ns;
put_cpu_no_resched();
}
spin_lock(&times->lock);
times->sum_exec_runtime += ns;
spin_unlock(&times->lock);
}

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