generic urcu deferral (call_rcu())

[urcu.git] / urcu-defer-static.h

diff --git a/urcu-defer-static.h b/urcu-defer-static.h
index 25137690465fa9c32ef5939be20d1cec3bdd17ad..7d0ed52cf88b624d5a236a5a35c3d1f8920ef661 100644 (file)
--- a/urcu-defer-static.h
+++ b/urcu-defer-static.h
@@ -42,6 +42,23 @@
 #define DEFER_QUEUE_SIZE       (1 << 12)
 #define DEFER_QUEUE_MASK       (DEFER_QUEUE_SIZE - 1)
 
+/*
+ * Typically, data is aligned at least on the architecture size.
+ * Use lowest bit to indicate that the current callback is changing.
+ * Assumes that (void *)-2L is not used often. Used to encode non-aligned
+ * functions and non-aligned data using extra space.
+ * We encode the (void *)-2L fct as: -2L, fct, data.
+ * We encode the (void *)-2L data as: -2L, fct, data.
+ * Here, DQ_FCT_MARK == ~DQ_FCT_BIT. Required for the test order.
+ */
+#define DQ_FCT_BIT             (1 << 0)
+#define DQ_IS_FCT_BIT(x)       ((unsigned long)(x) & DQ_FCT_BIT)
+#define DQ_SET_FCT_BIT(x)      \
+       (x = (void *)((unsigned long)(x) | DQ_FCT_BIT))
+#define DQ_CLEAR_FCT_BIT(x)    \
+       (x = (void *)((unsigned long)(x) & ~DQ_FCT_BIT))
+#define DQ_FCT_MARK            ((void *)(~DQ_FCT_BIT))
+
 /*
  * Identify a shared load. A smp_rmc() or smp_mc() should come before the load.
  */
@@ -86,9 +103,22 @@
 #define rcu_assert(args...)
 #endif
 
+/*
+ * defer queue.
+ * Contains pointers. Encoded to save space when same callback is often used.
+ * When looking up the next item:
+ * - if DQ_FCT_BIT is set, set the current callback to DQ_CLEAR_FCT_BIT(ptr)
+ *   - next element contains pointer to data.
+ * - else if item == DQ_FCT_MARK
+ *   - set the current callback to next element ptr
+ *   - following next element contains pointer to data.
+ * - else current element contains data
+ */
 struct defer_queue {
        unsigned long head;     /* add element at head */
+       void *last_fct_in;      /* last fct pointer encoded */
        unsigned long tail;     /* next element to remove at tail */
+       void *last_fct_out;     /* last fct pointer encoded */
        void **q;
 };
 
@@ -99,7 +129,7 @@ extern void rcu_defer_barrier_thread(void);
 /*
  * not signal-safe.
  */
-static inline void _rcu_defer_queue(void *p)
+static inline void _rcu_defer_queue(void (*fct)(void *p), void *p)
 {
        unsigned long head, tail;
 
@@ -112,17 +142,49 @@ static inline void _rcu_defer_queue(void *p)
 
        /*
         * If queue is full, empty it ourself.
+        * Worse-case: must allow 2 supplementary entries for fct pointer.
         */
-       if (unlikely(head - tail >= DEFER_QUEUE_SIZE)) {
-               assert(head - tail == DEFER_QUEUE_SIZE);
+       if (unlikely(head - tail >= DEFER_QUEUE_SIZE - 2)) {
+               assert(head - tail <= DEFER_QUEUE_SIZE);
                rcu_defer_barrier_thread();
                assert(head - LOAD_SHARED(defer_queue.tail) == 0);
        }
 
        smp_wmb();      /* Publish new pointer before write q[] */
-       _STORE_SHARED(defer_queue.q[head & DEFER_QUEUE_MASK], p);
+       if (unlikely(defer_queue.last_fct_in != fct)) {
+               //printf("fct diff %p %p\n", defer_queue.last_fct, fct);
+               defer_queue.last_fct_in = fct;
+               if (unlikely(DQ_IS_FCT_BIT(fct) || fct == DQ_FCT_MARK)) {
+                       /*
+                        * If the function to encode is not aligned or the
+                        * marker, write DQ_FCT_MARK followed by the function
+                        * pointer.
+                        */
+                       _STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
+                                     DQ_FCT_MARK);
+                       _STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
+                                     fct);
+               } else {
+                       DQ_SET_FCT_BIT(fct);
+                       _STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
+                                     fct);
+               }
+       } else {
+               //printf("fct same %p\n", fct);
+               if (unlikely(DQ_IS_FCT_BIT(p) || p == DQ_FCT_MARK)) {
+                       /*
+                        * If the data to encode is not aligned or the marker,
+                        * write DQ_FCT_MARK followed by the function pointer.
+                        */
+                       _STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
+                                     DQ_FCT_MARK);
+                       _STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK],
+                                     fct);
+               }
+       }
+       _STORE_SHARED(defer_queue.q[head++ & DEFER_QUEUE_MASK], p);
        smp_wmb();      /* Write q[] before head. */
-       STORE_SHARED(defer_queue.head, head + 1);
+       STORE_SHARED(defer_queue.head, head);
 }
 
 #endif /* _URCU_DEFER_STATIC_H */