posix_timers: New API to prevent from stopping the tick when timers are running

Bring a new helper that the full dynticks infrastructure can
call in order to know if it can safely stop the tick from
the posix cpu timers subsystem point of view.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Geoff Levand <geoff@infradead.org>
Cc: Gilad Ben Yossef <gilad@benyossef.com>
Cc: Hakan Akkan <hakanakkan@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Kevin Hilman <khilman@linaro.org>
Cc: Li Zhong <zhong@linux.vnet.ibm.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 26 insertions, 15 deletions

diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
index 0bc33561a435..84d5cb372ed5 100644
--- a/kernel/posix-cpu-timers.c
+++ b/kernel/posix-cpu-timers.c
@@ -155,6 +155,21 @@ static void bump_cpu_timer(struct k_itimer *timer,
         }
 }
 
+/**
+ * task_cputime_zero - Check a task_cputime struct for all zero fields.
+ *
+ * @cputime:    The struct to compare.
+ *
+ * Checks @cputime to see if all fields are zero.  Returns true if all fields
+ * are zero, false if any field is nonzero.
+ */
+static inline int task_cputime_zero(const struct task_cputime *cputime)
+{
+        if (!cputime->utime && !cputime->stime && !cputime->sum_exec_runtime)
+                return 1;
+        return 0;
+}
+
 static inline cputime_t prof_ticks(struct task_struct *p)
 {
         cputime_t utime, stime;
@@ -654,6 +669,17 @@ static void posix_cpu_timer_kick_nohz(void)
 {
         schedule_work(&nohz_kick_work);
 }
+
+bool posix_cpu_timers_can_stop_tick(struct task_struct *tsk)
+{
+        if (!task_cputime_zero(&tsk->cputime_expires))
+                return true;
+
+        if (tsk->signal->cputimer.running)
+                return true;
+
+        return false;
+}
 #else
 static inline void posix_cpu_timer_kick_nohz(void) { }
 #endif
@@ -1032,21 +1058,6 @@ static void check_cpu_itimer(struct task_struct *tsk, struct cpu_itimer *it,
         }
 }
 
-/**
- * task_cputime_zero - Check a task_cputime struct for all zero fields.
- *
- * @cputime:    The struct to compare.
- *
- * Checks @cputime to see if all fields are zero.  Returns true if all fields
- * are zero, false if any field is nonzero.
- */
-static inline int task_cputime_zero(const struct task_cputime *cputime)
-{
-        if (!cputime->utime && !cputime->stime && !cputime->sum_exec_runtime)
-                return 1;
-        return 0;
-}
-
 /*
  * Check for any per-thread CPU timers that have fired and move them
  * off the tsk->*_timers list onto the firing list.  Per-thread timers