[PATCH] Reduce stack usage in itimer.c

From: Yum Rayan (yum.rayan_at_gmail.com)
Date: 03/31/05

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Date:	Wed, 30 Mar 2005 23:43:05 -0800
To: linux-kernel@vger.kernel.org

Attempt to reduce stack usage in itimer.c (linux-2.6.12-rc1-mm3). Stack
usage was noted using checkstack.pl. Specifically

Before patch
------------
do_setitimer - 160

After patch
-----------
do_setitimer - none
do_setitimer_real 52
do_setitimer_virtual 52
do_setitimer_prof 52

A singularly heavy stack user do_setitimer(...) was broken down into 3
separate functions. Stack usage will now be lower depending on the path taken.

Signed-off-by: Yum Rayan <yum.rayan@gmail.com>

--- a/kernel/itimer.c 2005-03-25 22:10:33.000000000 -0800
+++ b/kernel/itimer.c 2005-03-30 15:59:11.000000000 -0800
@@ -141,83 +141,95 @@
         it_real_arm(p, p->signal->it_real_incr);
}

-int do_setitimer(int which, struct itimerval *value, struct itimerval *ovalue)
+static void do_setitimer_real(struct itimerval *value, struct
itimerval *ovalue)
{
         struct task_struct *tsk = current;
          unsigned long val, interval;
+
+ spin_lock_irq(&tsk->sighand->siglock);
+ interval = tsk->signal->it_real_incr;
+ val = it_real_value(tsk->signal);
+ if (val)
+ del_timer_sync(&tsk->signal->real_timer);
+ tsk->signal->it_real_incr = timeval_to_jiffies(&value->it_interval);
+ it_real_arm(tsk, timeval_to_jiffies(&value->it_value));
+ spin_unlock_irq(&tsk->sighand->siglock);
+ if (ovalue) {
+ jiffies_to_timeval(val, &ovalue->it_value);
+ jiffies_to_timeval(interval, &ovalue->it_interval);
+ }
+}
+
+static void do_setitimer_virtual(struct itimerval *value,
+ struct itimerval *ovalue)
+{
+ struct task_struct *tsk = current;
+ cputime_t cval, cinterval, nval, ninterval;
+
+ nval = timeval_to_cputime(&value->it_value);
+ ninterval = timeval_to_cputime(&value->it_interval);
+ read_lock(&tasklist_lock);
+ spin_lock_irq(&tsk->sighand->siglock);
+ cval = tsk->signal->it_virt_expires;
+ cinterval = tsk->signal->it_virt_incr;
+ if (!cputime_eq(cval, cputime_zero) ||
+ !cputime_eq(nval, cputime_zero)) {
+ if (cputime_gt(nval, cputime_zero))
+ nval = cputime_add(nval, jiffies_to_cputime(1));
+ set_process_cpu_timer(tsk, CPUCLOCK_VIRT, &nval, &cval);
+ }
+ tsk->signal->it_virt_expires = nval;
+ tsk->signal->it_virt_incr = ninterval;
+ spin_unlock_irq(&tsk->sighand->siglock);
+ read_unlock(&tasklist_lock);
+ if (ovalue) {
+ cputime_to_timeval(cval, &ovalue->it_value);
+ cputime_to_timeval(cinterval, &ovalue->it_interval);
+ }
+}
+static void do_setitimer_prof(struct itimerval *value, struct
itimerval *ovalue)
+{
+ struct task_struct *tsk = current;
         cputime_t cval, cinterval, nval, ninterval;
+ nval = timeval_to_cputime(&value->it_value);
+ ninterval = timeval_to_cputime(&value->it_interval);
+ read_lock(&tasklist_lock);
+ spin_lock_irq(&tsk->sighand->siglock);
+ cval = tsk->signal->it_prof_expires;
+ cinterval = tsk->signal->it_prof_incr;
+ if (!cputime_eq(cval, cputime_zero) ||
+ !cputime_eq(nval, cputime_zero)) {
+ if (cputime_gt(nval, cputime_zero))
+ nval = cputime_add(nval, jiffies_to_cputime(1));
+ set_process_cpu_timer(tsk, CPUCLOCK_PROF, &nval, &cval);
+ }
+ tsk->signal->it_prof_expires = nval;
+ tsk->signal->it_prof_incr = ninterval;
+ spin_unlock_irq(&tsk->sighand->siglock);
+ read_unlock(&tasklist_lock);
+ if (ovalue) {
+ cputime_to_timeval(cval, &ovalue->it_value);
+ cputime_to_timeval(cinterval, &ovalue->it_interval);
+ }
+}

+int do_setitimer(int which, struct itimerval *value, struct itimerval *ovalue)
+{
         switch (which) {
         case ITIMER_REAL:
- spin_lock_irq(&tsk->sighand->siglock);
- interval = tsk->signal->it_real_incr;
- val = it_real_value(tsk->signal);
- if (val)
- del_timer_sync(&tsk->signal->real_timer);
- tsk->signal->it_real_incr =
- timeval_to_jiffies(&value->it_interval);
- it_real_arm(tsk, timeval_to_jiffies(&value->it_value));
- spin_unlock_irq(&tsk->sighand->siglock);
- if (ovalue) {
- jiffies_to_timeval(val, &ovalue->it_value);
- jiffies_to_timeval(interval,
- &ovalue->it_interval);
- }
+ do_setitimer_real(value, ovalue);
                 break;
         case ITIMER_VIRTUAL:
- nval = timeval_to_cputime(&value->it_value);
- ninterval = timeval_to_cputime(&value->it_interval);
- read_lock(&tasklist_lock);
- spin_lock_irq(&tsk->sighand->siglock);
- cval = tsk->signal->it_virt_expires;
- cinterval = tsk->signal->it_virt_incr;
- if (!cputime_eq(cval, cputime_zero) ||
- !cputime_eq(nval, cputime_zero)) {
- if (cputime_gt(nval, cputime_zero))
- nval = cputime_add(nval,
- jiffies_to_cputime(1));
- set_process_cpu_timer(tsk, CPUCLOCK_VIRT,
- &nval, &cval);
- }
- tsk->signal->it_virt_expires = nval;
- tsk->signal->it_virt_incr = ninterval;
- spin_unlock_irq(&tsk->sighand->siglock);
- read_unlock(&tasklist_lock);
- if (ovalue) {
- cputime_to_timeval(cval, &ovalue->it_value);
- cputime_to_timeval(cinterval, &ovalue->it_interval);
- }
+ do_setitimer_virtual(value, ovalue);
                 break;
         case ITIMER_PROF:
- nval = timeval_to_cputime(&value->it_value);
- ninterval = timeval_to_cputime(&value->it_interval);
- read_lock(&tasklist_lock);
- spin_lock_irq(&tsk->sighand->siglock);
- cval = tsk->signal->it_prof_expires;
- cinterval = tsk->signal->it_prof_incr;
- if (!cputime_eq(cval, cputime_zero) ||
- !cputime_eq(nval, cputime_zero)) {
- if (cputime_gt(nval, cputime_zero))
- nval = cputime_add(nval,
- jiffies_to_cputime(1));
- set_process_cpu_timer(tsk, CPUCLOCK_PROF,
- &nval, &cval);
- }
- tsk->signal->it_prof_expires = nval;
- tsk->signal->it_prof_incr = ninterval;
- spin_unlock_irq(&tsk->sighand->siglock);
- read_unlock(&tasklist_lock);
- if (ovalue) {
- cputime_to_timeval(cval, &ovalue->it_value);
- cputime_to_timeval(cinterval, &ovalue->it_interval);
- }
+ do_setitimer_prof(value, ovalue);
                 break;
         default:
                 return -EINVAL;
         }
         return 0;
}
-
asmlinkage long sys_setitimer(int which,
                               struct itimerval __user *value,
                               struct itimerval __user *ovalue)
-
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