Merge tag 'full-dynticks-cputime-for-mingo' of git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks into sched/core

Pull full-dynticks (user-space execution is undisturbed and
receives no timer IRQs) preparation changes that convert the
cputime accounting code to be full-dynticks ready,
from Frederic Weisbecker:

 "This implements the cputime accounting on full dynticks CPUs.

  Typical cputime stats infrastructure relies on the timer tick and
  its periodic polling on the CPU to account the amount of time
  spent by the CPUs and the tasks per high level domains such as
  userspace, kernelspace, guest, ...

  Now we are preparing to implement full dynticks capability on
  Linux for Real Time and HPC users who want full CPU isolation.
  This feature requires a cputime accounting that doesn't depend
  on the timer tick.

  To implement it, this new cputime infrastructure plugs into
  kernel/user/guest boundaries to take snapshots of cputime and
  flush these to the stats when needed. This performs pretty
  much like CONFIG_VIRT_CPU_ACCOUNTING except that context location
  and cputime snaphots are synchronized between write and read
  side such that the latter can safely retrieve the pending tickless
  cputime of a task and add it to its latest cputime snapshot to
  return the correct result to the user."

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 28 insertions, 0 deletions

diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h
index e24339c..b28d161 100644
--- a/include/linux/context_tracking.h
+++ b/include/linux/context_tracking.h
@@ -3,12 +3,40 @@
 
 #ifdef CONFIG_CONTEXT_TRACKING
 #include <linux/sched.h>
+#include <linux/percpu.h>
+
+struct context_tracking {
+	/*
+	 * When active is false, probes are unset in order
+	 * to minimize overhead: TIF flags are cleared
+	 * and calls to user_enter/exit are ignored. This
+	 * may be further optimized using static keys.
+	 */
+	bool active;
+	enum {
+		IN_KERNEL = 0,
+		IN_USER,
+	} state;
+};
+
+DECLARE_PER_CPU(struct context_tracking, context_tracking);
+
+static inline bool context_tracking_in_user(void)
+{
+	return __this_cpu_read(context_tracking.state) == IN_USER;
+}
+
+static inline bool context_tracking_active(void)
+{
+	return __this_cpu_read(context_tracking.active);
+}
 
 extern void user_enter(void);
 extern void user_exit(void);
 extern void context_tracking_task_switch(struct task_struct *prev,
 					 struct task_struct *next);
 #else
+static inline bool context_tracking_in_user(void) { return false; }
 static inline void user_enter(void) { }
 static inline void user_exit(void) { }
 static inline void context_tracking_task_switch(struct task_struct *prev,