Merge branch 'timers/core-v9' of git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks into timers/nohz

Pull nohz enhancements from Frederic Weisbecker:

"Currently in nohz full configs, the tick dependency is checked
 asynchronously by nohz code from interrupt and context switch for each
 concerned subsystem with a set of function provided by these. Such
 functions are made of many conditions and details that can be heavyweight
 as they are called on fastpath: sched_can_stop_tick(),
 posix_cpu_timer_can_stop_tick(), perf_event_can_stop_tick()...

 Thomas suggested a few months ago to make that tick dependency check
 synchronous. Instead of checking subsystems details from each interrupt
 to guess if the tick can be stopped, every subsystem that may have a tick
 dependency should set itself a flag specifying the state of that
 dependency. This way we can verify if we can stop the tick with a single
 lightweight mask check on fast path.

 This conversion from a pull to a push model to implement tick dependency
 is the core feature of this patchset that is split into:

  * Nohz wide kick simplification
  * Improve nohz tracing
  * Introduce tick dependency mask
  * Migrate scheduler, posix timers, perf events and sched clock tick
    dependencies to the tick dependency mask."

Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 21 insertions, 0 deletions

diff --git a/include/linux/atomic.h b/include/linux/atomic.h
index 301de78d65f7..6c502cb13c95 100644
--- a/include/linux/atomic.h
+++ b/include/linux/atomic.h
@@ -548,6 +548,27 @@ static inline int atomic_dec_if_positive(atomic_t *v)
 }
 #endif
 
+/**
+ * fetch_or - perform *ptr |= mask and return old value of *ptr
+ * @ptr: pointer to value
+ * @mask: mask to OR on the value
+ *
+ * cmpxchg based fetch_or, macro so it works for different integer types
+ */
+#ifndef fetch_or
+#define fetch_or(ptr, mask)                                             \
+({      typeof(*(ptr)) __old, __val = *(ptr);                           \
+        for (;;) {                                                      \
+                __old = cmpxchg((ptr), __val, __val | (mask));          \
+                if (__old == __val)                                     \
+                        break;                                          \
+                __val = __old;                                          \
+        }                                                               \
+        __old;                                                          \
+})
+#endif
+
+
 #ifdef CONFIG_GENERIC_ATOMIC64
 #include <asm-generic/atomic64.h>
 #endif