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Subject[PATCH tip/sched/core] introduce task_times() to replace task_[us]time() pair
Function task_[us]times() are called consecutively in almost all
cases. However task_stime() is implemented to call task_utime()
from its inside, so such paired calls run task_utime() twice.

It means we do heavy divisions (div_u64 + do_div) twice to get
stime and utime which can be obtained at same time by one set
of divisions.

This patch introduces task_times(*tsk, *utime, *stime) to get
stime and utime at once, in better, optimized way.

Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
---
fs/proc/array.c | 3 +-
include/linux/sched.h | 1 +
kernel/exit.c | 7 ++++-
kernel/sched.c | 55 +++++++++++++++++++++++++++++++-----------------
kernel/sys.c | 3 +-
5 files changed, 43 insertions(+), 26 deletions(-)
diff --git a/fs/proc/array.c b/fs/proc/array.c
index e209f64..330deda 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -535,8 +535,7 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
if (!whole) {
min_flt = task->min_flt;
maj_flt = task->maj_flt;
- utime = task_utime(task);
- stime = task_stime(task);
+ task_times(task, &utime, &stime);
gtime = task_gtime(task);
}

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 78ba664..fe6ae15 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1723,6 +1723,7 @@ static inline void put_task_struct(struct task_struct *t)
extern cputime_t task_utime(struct task_struct *p);
extern cputime_t task_stime(struct task_struct *p);
extern cputime_t task_gtime(struct task_struct *p);
+extern void task_times(struct task_struct *p, cputime_t *ut, cputime_t *st);

/*
* Per process flags
diff --git a/kernel/exit.c b/kernel/exit.c
index e61891f..a19e429 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -91,6 +91,8 @@ static void __exit_signal(struct task_struct *tsk)
if (atomic_dec_and_test(&sig->count))
posix_cpu_timers_exit_group(tsk);
else {
+ cputime_t utime, stime;
+
/*
* If there is any task waiting for the group exit
* then notify it:
@@ -110,8 +112,9 @@ static void __exit_signal(struct task_struct *tsk)
* We won't ever get here for the group leader, since it
* will have been the last reference on the signal_struct.
*/
- sig->utime = cputime_add(sig->utime, task_utime(tsk));
- sig->stime = cputime_add(sig->stime, task_stime(tsk));
+ task_times(tsk, &utime, &stime);
+ sig->utime = cputime_add(sig->utime, utime);
+ sig->stime = cputime_add(sig->stime, stime);
sig->gtime = cputime_add(sig->gtime, task_gtime(tsk));
sig->min_flt += tsk->min_flt;
sig->maj_flt += tsk->maj_flt;
diff --git a/kernel/sched.c b/kernel/sched.c
index ab9a034..18c89e0 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -5155,6 +5155,14 @@ cputime_t task_stime(struct task_struct *p)
{
return p->stime;
}
+
+void task_times(struct task_struct *p, cputime_t *ut, cputime_t *st)
+{
+ if (ut)
+ *ut = task_utime(p);
+ if (st)
+ *st = task_stime(p);
+}
#else

#ifndef nsecs_to_cputime
@@ -5162,41 +5170,48 @@ cputime_t task_stime(struct task_struct *p)
msecs_to_cputime(div_u64((__nsecs), NSEC_PER_MSEC))
#endif

-cputime_t task_utime(struct task_struct *p)
+void task_times(struct task_struct *p, cputime_t *ut, cputime_t *st)
{
- cputime_t utime = p->utime, total = utime + p->stime;
- u64 temp;
+ cputime_t rtime, utime = p->utime, total = utime + p->stime;

/*
* Use CFS's precise accounting:
*/
- temp = (u64)nsecs_to_cputime(p->se.sum_exec_runtime);
+ rtime = nsecs_to_cputime(p->se.sum_exec_runtime);

if (total) {
- temp *= utime;
+ u64 temp;
+
+ temp = (u64)(rtime * utime);
do_div(temp, total);
- }
- utime = (cputime_t)temp;
+ utime = (cputime_t)temp;
+ } else
+ utime = rtime;

+ /*
+ * Compare with previous values, to keep monotonicity:
+ */
p->prev_utime = max(p->prev_utime, utime);
- return p->prev_utime;
+ p->prev_stime = max(p->prev_stime, rtime - p->prev_utime);
+
+ if (ut)
+ *ut = p->prev_utime;
+ if (st)
+ *st = p->prev_stime;
+}
+
+cputime_t task_utime(struct task_struct *p)
+{
+ cputime_t utime;
+ task_times(p, &utime, NULL);
+ return utime;
}

cputime_t task_stime(struct task_struct *p)
{
cputime_t stime;
-
- /*
- * Use CFS's precise accounting. (we subtract utime from
- * the total, to make sure the total observed by userspace
- * grows monotonically - apps rely on that):
- */
- stime = nsecs_to_cputime(p->se.sum_exec_runtime) - task_utime(p);
-
- if (stime >= 0)
- p->prev_stime = max(p->prev_stime, stime);
-
- return p->prev_stime;
+ task_times(p, NULL, &stime);
+ return stime;
}
#endif

diff --git a/kernel/sys.c b/kernel/sys.c
index 255475d..b6caf1e 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1344,8 +1344,7 @@ static void k_getrusage(struct task_struct *p, int who, struct rusage *r)
utime = stime = cputime_zero;

if (who == RUSAGE_THREAD) {
- utime = task_utime(current);
- stime = task_stime(current);
+ task_times(current, &utime, &stime);
accumulate_thread_rusage(p, r);
maxrss = p->signal->maxrss;
goto out;
--
1.6.5.3


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