[PATCH] hrtimer: switch itimers to hrtimer

switch itimers to a hrtimers-based implementation

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

3 files changed, 55 insertions, 59 deletions

diff --git a/kernel/exit.c b/kernel/exit.c
index 309a46fa16f8..e75a51f33768 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -842,7 +842,7 @@ fastcall NORET_TYPE void do_exit(long code)
         }
         group_dead = atomic_dec_and_test(&tsk->signal->live);
         if (group_dead) {
-                del_timer_sync(&tsk->signal->real_timer);
+                hrtimer_cancel(&tsk->signal->real_timer);
                 exit_itimers(tsk->signal);
                 acct_process(code);
         }
diff --git a/kernel/fork.c b/kernel/fork.c
index b18d64554feb..3bdcab49998d 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -801,10 +801,10 @@ static inline int copy_signal(unsigned long clone_flags, struct task_struct * ts
         init_sigpending(&sig->shared_pending);
         INIT_LIST_HEAD(&sig->posix_timers);
 
-        sig->it_real_value = sig->it_real_incr = 0;
+        hrtimer_init(&sig->real_timer, CLOCK_MONOTONIC);
+        sig->it_real_incr.tv64 = 0;
         sig->real_timer.function = it_real_fn;
-        sig->real_timer.data = (unsigned long) tsk;
-        init_timer(&sig->real_timer);
+        sig->real_timer.data = tsk;
 
         sig->it_virt_expires = cputime_zero;
         sig->it_virt_incr = cputime_zero;
diff --git a/kernel/itimer.c b/kernel/itimer.c
index 7c1b25e25e47..c2c05c4ff28d 100644
--- a/kernel/itimer.c
+++ b/kernel/itimer.c
@@ -12,36 +12,46 @@
 #include <linux/syscalls.h>
 #include <linux/time.h>
 #include <linux/posix-timers.h>
+#include <linux/hrtimer.h>
 
 #include <asm/uaccess.h>
 
-static unsigned long it_real_value(struct signal_struct *sig)
+/**
+ * itimer_get_remtime - get remaining time for the timer
+ *
+ * @timer: the timer to read
+ *
+ * Returns the delta between the expiry time and now, which can be
+ * less than zero or 1usec for an pending expired timer
+ */
+static struct timeval itimer_get_remtime(struct hrtimer *timer)
 {
-        unsigned long val = 0;
-        if (timer_pending(&sig->real_timer)) {
-                val = sig->real_timer.expires - jiffies;
+        ktime_t rem = hrtimer_get_remaining(timer);
 
-                /* look out for negative/zero itimer.. */
-                if ((long) val <= 0)
-                        val = 1;
-        }
-        return val;
+        /*
+         * Racy but safe: if the itimer expires after the above
+         * hrtimer_get_remtime() call but before this condition
+         * then we return 0 - which is correct.
+         */
+        if (hrtimer_active(timer)) {
+                if (rem.tv64 <= 0)
+                        rem.tv64 = NSEC_PER_USEC;
+        } else
+                rem.tv64 = 0;
+
+        return ktime_to_timeval(rem);
 }
 
 int do_getitimer(int which, struct itimerval *value)
 {
         struct task_struct *tsk = current;
-        unsigned long interval, val;
         cputime_t cinterval, cval;
 
         switch (which) {
         case ITIMER_REAL:
-                spin_lock_irq(&tsk->sighand->siglock);
-                interval = tsk->signal->it_real_incr;
-                val = it_real_value(tsk->signal);
-                spin_unlock_irq(&tsk->sighand->siglock);
-                jiffies_to_timeval(val, &value->it_value);
-                jiffies_to_timeval(interval, &value->it_interval);
+                value->it_value = itimer_get_remtime(&tsk->signal->real_timer);
+                value->it_interval =
+                        ktime_to_timeval(tsk->signal->it_real_incr);
                 break;
         case ITIMER_VIRTUAL:
                 read_lock(&tasklist_lock);
@@ -113,59 +123,45 @@ asmlinkage long sys_getitimer(int which, struct itimerval __user *value)
 }
 
 
-void it_real_fn(unsigned long __data)
+/*
+ * The timer is automagically restarted, when interval != 0
+ */
+int it_real_fn(void *data)
 {
-        struct task_struct * p = (struct task_struct *) __data;
-        unsigned long inc = p->signal->it_real_incr;
+        struct task_struct *tsk = (struct task_struct *) data;
 
-        send_group_sig_info(SIGALRM, SEND_SIG_PRIV, p);
+        send_group_sig_info(SIGALRM, SEND_SIG_PRIV, tsk);
 
-        /*
-         * Now restart the timer if necessary.  We don't need any locking
-         * here because do_setitimer makes sure we have finished running
-         * before it touches anything.
-         * Note, we KNOW we are (or should be) at a jiffie edge here so
-         * we don't need the +1 stuff.  Also, we want to use the prior
-         * expire value so as to not "slip" a jiffie if we are late.
-         * Deal with requesting a time prior to "now" here rather than
-         * in add_timer.
-         */
-        if (!inc)
-                return;
-        while (time_before_eq(p->signal->real_timer.expires, jiffies))
-                p->signal->real_timer.expires += inc;
-        add_timer(&p->signal->real_timer);
+        if (tsk->signal->it_real_incr.tv64 != 0) {
+                hrtimer_forward(&tsk->signal->real_timer,
+                               tsk->signal->it_real_incr);
+
+                return HRTIMER_RESTART;
+        }
+        return HRTIMER_NORESTART;
 }
 
 int do_setitimer(int which, struct itimerval *value, struct itimerval *ovalue)
 {
         struct task_struct *tsk = current;
-        unsigned long val, interval, expires;
+        struct hrtimer *timer;
+        ktime_t expires;
         cputime_t cval, cinterval, nval, ninterval;
 
         switch (which) {
         case ITIMER_REAL:
-again:
-                spin_lock_irq(&tsk->sighand->siglock);
-                interval = tsk->signal->it_real_incr;
-                val = it_real_value(tsk->signal);
-                /* We are sharing ->siglock with it_real_fn() */
-                if (try_to_del_timer_sync(&tsk->signal->real_timer) < 0) {
-                        spin_unlock_irq(&tsk->sighand->siglock);
-                        goto again;
-                }
-                tsk->signal->it_real_incr =
-                        timeval_to_jiffies(&value->it_interval);
-                expires = timeval_to_jiffies(&value->it_value);
-                if (expires)
-                        mod_timer(&tsk->signal->real_timer,
-                                  jiffies + 1 + expires);
-                spin_unlock_irq(&tsk->sighand->siglock);
+                timer = &tsk->signal->real_timer;
+                hrtimer_cancel(timer);
                 if (ovalue) {
-                        jiffies_to_timeval(val, &ovalue->it_value);
-                        jiffies_to_timeval(interval,
-                                           &ovalue->it_interval);
+                        ovalue->it_value = itimer_get_remtime(timer);
+                        ovalue->it_interval
+                                = ktime_to_timeval(tsk->signal->it_real_incr);
                 }
+                tsk->signal->it_real_incr =
+                        timeval_to_ktime(value->it_interval);
+                expires = timeval_to_ktime(value->it_value);
+                if (expires.tv64 != 0)
+                        hrtimer_start(timer, expires, HRTIMER_REL);
                 break;
         case ITIMER_VIRTUAL:
                 nval = timeval_to_cputime(&value->it_value);