* Distributed under GPLv2
*/
+#include <stdlib.h>
+#include <pthread.h>
+
/* The "volatile" is due to gcc bugs */
#define barrier() __asm__ __volatile__("": : :"memory")
+#define likely(x) __builtin_expect(!!(x), 1)
+#define unlikely(x) __builtin_expect(!!(x), 0)
+
+/*
+ * Assume the architecture has coherent caches. Blackfin will want this unset.
+ */
+#define CONFIG_HAVE_MEM_COHERENCY 1
+
+/* Assume P4 or newer */
+#define CONFIG_HAVE_FENCE 1
+
+/* Assume SMP machine, given we don't have this information */
+#define CONFIG_SMP 1
+
+
+#ifdef CONFIG_HAVE_MEM_COHERENCY
+/*
+ * Caches are coherent, no need to flush them.
+ */
+#define mc() barrier()
+#define rmc() barrier()
+#define wmc() barrier()
+#else
+#error "The architecture must create its own cache flush primitives"
+#define mc() arch_cache_flush()
+#define rmc() arch_cache_flush_read()
+#define wmc() arch_cache_flush_write()
+#endif
+
+
+#ifdef CONFIG_HAVE_MEM_COHERENCY
+
/* x86 32/64 specific */
+#ifdef CONFIG_HAVE_FENCE
#define mb() asm volatile("mfence":::"memory")
#define rmb() asm volatile("lfence":::"memory")
-#define wmb() asm volatile("sfence" ::: "memory")
+#define wmb() asm volatile("sfence"::: "memory")
+#else
+/*
+ * Some non-Intel clones support out of order store. wmb() ceases to be a
+ * nop for these.
+ */
+#define mb() asm volatile("lock; addl $0,0(%%esp)":::"memory")
+#define rmb() asm volatile("lock; addl $0,0(%%esp)":::"memory")
+#define wmb() asm volatile("lock; addl $0,0(%%esp)"::: "memory")
+#endif
+
+#else /* !CONFIG_HAVE_MEM_COHERENCY */
+
+/*
+ * Without cache coherency, the memory barriers become cache flushes.
+ */
+#define mb() mc()
+#define rmb() rmc()
+#define wmb() wmc()
+
+#endif /* !CONFIG_HAVE_MEM_COHERENCY */
+
+
+#ifdef CONFIG_SMP
+#define smp_mb() mb()
+#define smp_rmb() rmb()
+#define smp_wmb() wmb()
+#define smp_mc() mc()
+#define smp_rmc() rmc()
+#define smp_wmc() wmc()
+#else
+#define smp_mb() barrier()
+#define smp_rmb() barrier()
+#define smp_wmb() barrier()
+#define smp_mc() barrier()
+#define smp_rmc() barrier()
+#define smp_wmc() barrier()
+#endif
+
+/* REP NOP (PAUSE) is a good thing to insert into busy-wait loops. */
+static inline void rep_nop(void)
+{
+ asm volatile("rep; nop" ::: "memory");
+}
+
+static inline void cpu_relax(void)
+{
+ rep_nop();
+}
static inline void atomic_inc(int *v)
{
: "+m" (*v));
}
+#define xchg(ptr, v) \
+ ((__typeof__(*(ptr)))__xchg((unsigned long)(v), (ptr), sizeof(*(ptr))))
+
+struct __xchg_dummy {
+ unsigned long a[100];
+};
+#define __xg(x) ((struct __xchg_dummy *)(x))
+
+/*
+ * Note: no "lock" prefix even on SMP: xchg always implies lock anyway
+ * Note 2: xchg has side effect, so that attribute volatile is necessary,
+ * but generally the primitive is invalid, *ptr is output argument. --ANK
+ * x is considered local, ptr is considered remote.
+ */
+static inline unsigned long __xchg(unsigned long x, volatile void *ptr,
+ int size)
+{
+ switch (size) {
+ case 1:
+ asm volatile("xchgb %b0,%1"
+ : "=q" (x)
+ : "m" (*__xg(ptr)), "0" (x)
+ : "memory");
+ break;
+ case 2:
+ asm volatile("xchgw %w0,%1"
+ : "=r" (x)
+ : "m" (*__xg(ptr)), "0" (x)
+ : "memory");
+ break;
+ case 4:
+ asm volatile("xchgl %k0,%1"
+ : "=r" (x)
+ : "m" (*__xg(ptr)), "0" (x)
+ : "memory");
+ break;
+ case 8:
+ asm volatile("xchgq %0,%1"
+ : "=r" (x)
+ : "m" (*__xg(ptr)), "0" (x)
+ : "memory");
+ break;
+ }
+ smp_wmc();
+ return x;
+}
+
/* Nop everywhere except on alpha. */
#define smp_read_barrier_depends()
*/
#define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x))
+/*
+ * Load a data from shared memory, doing a cache flush if required.
+ */
+#define LOAD_SHARED(p) ({ \
+ smp_rmc(); \
+ typeof(p) _________p1 = ACCESS_ONCE(p); \
+ (_________p1); \
+ })
+
+/*
+ * Store v into x, where x is located in shared memory. Performs the required
+ * cache flush after writing.
+ */
+#define STORE_SHARED(x, v) \
+ do { \
+ (x) = (v); \
+ smp_wmc; \
+ } while (0)
+
/**
* rcu_dereference - fetch an RCU-protected pointer in an
* RCU read-side critical section. This pointer may later
*/
#define rcu_dereference(p) ({ \
- typeof(p) _________p1 = ACCESS_ONCE(p); \
+ typeof(p) _________p1 = LOAD_SHARED(p); \
smp_read_barrier_depends(); \
(_________p1); \
})
+
+
#define SIGURCU SIGUSR1
+/*
+ * If a reader is really non-cooperative and refuses to commit its
+ * urcu_active_readers count to memory (there is no barrier in the reader
+ * per-se), kick it after a few loops waiting for it.
+ */
+#define KICK_READER_LOOPS 10000
+
#ifdef DEBUG_YIELD
#include <sched.h>
+#include <time.h>
+#include <pthread.h>
+#include <unistd.h>
#define YIELD_READ (1 << 0)
#define YIELD_WRITE (1 << 1)
+/* Updates without DEBUG_FULL_MB are much slower. Account this in the delay */
+#ifdef DEBUG_FULL_MB
+/* maximum sleep delay, in us */
+#define MAX_SLEEP 50
+#else
+#define MAX_SLEEP 30000
+#endif
+
extern unsigned int yield_active;
extern unsigned int __thread rand_yield;
{
if (yield_active & YIELD_READ)
if (rand_r(&rand_yield) & 0x1)
- sched_yield();
+ usleep(rand_r(&rand_yield) % MAX_SLEEP);
}
static inline void debug_yield_write(void)
{
if (yield_active & YIELD_WRITE)
if (rand_r(&rand_yield) & 0x1)
- sched_yield();
+ usleep(rand_r(&rand_yield) % MAX_SLEEP);
}
static inline void debug_yield_init(void)
}
#endif
-/* Global quiescent period parity */
-extern int urcu_qparity;
-
-extern int __thread urcu_active_readers[2];
-
-static inline int get_urcu_qparity(void)
+#ifdef DEBUG_FULL_MB
+static inline void reader_barrier()
{
- return urcu_qparity;
+ smp_mb();
}
+#else
+static inline void reader_barrier()
+{
+ barrier();
+}
+#endif
+
+/*
+ * The trick here is that RCU_GP_CTR_BIT must be a multiple of 8 so we can use a
+ * full 8-bits, 16-bits or 32-bits bitmask for the lower order bits.
+ */
+#define RCU_GP_COUNT (1UL << 0)
+/* Use the amount of bits equal to half of the architecture long size */
+#define RCU_GP_CTR_BIT (1UL << (sizeof(long) << 2))
+#define RCU_GP_CTR_NEST_MASK (RCU_GP_CTR_BIT - 1)
/*
- * urcu_parity should be declared on the caller's stack.
+ * Global quiescent period counter with low-order bits unused.
+ * Using a int rather than a char to eliminate false register dependencies
+ * causing stalls on some architectures.
*/
-static inline void rcu_read_lock(int *urcu_parity)
+extern long urcu_gp_ctr;
+
+extern long __thread urcu_active_readers;
+
+static inline int rcu_old_gp_ongoing(long *value)
+{
+ long v;
+
+ if (value == NULL)
+ return 0;
+ /*
+ * Make sure both tests below are done on the same version of *value
+ * to insure consistency.
+ */
+ v = LOAD_SHARED(*value);
+ return (v & RCU_GP_CTR_NEST_MASK) &&
+ ((v ^ urcu_gp_ctr) & RCU_GP_CTR_BIT);
+}
+
+static inline void rcu_read_lock(void)
{
- debug_yield_read();
- *urcu_parity = get_urcu_qparity();
- debug_yield_read();
- urcu_active_readers[*urcu_parity]++;
- debug_yield_read();
+ long tmp;
+
+ tmp = urcu_active_readers;
+ /* urcu_gp_ctr = RCU_GP_COUNT | (~RCU_GP_CTR_BIT or RCU_GP_CTR_BIT) */
+ /*
+ * The data dependency "read urcu_gp_ctr, write urcu_active_readers",
+ * serializes those two memory operations. We are not using STORE_SHARED
+ * and LOAD_SHARED here (although we should) because the writer will
+ * wake us up with a signal which does a flush in its handler to perform
+ * urcu_gp_ctr re-read and urcu_active_readers commit to main memory.
+ */
+ if (likely(!(tmp & RCU_GP_CTR_NEST_MASK)))
+ urcu_active_readers = ACCESS_ONCE(urcu_gp_ctr);
+ else
+ urcu_active_readers = tmp + RCU_GP_COUNT;
/*
* Increment active readers count before accessing the pointer.
* See force_mb_all_threads().
*/
- barrier();
- debug_yield_read();
+ reader_barrier();
}
-static inline void rcu_read_unlock(int *urcu_parity)
+static inline void rcu_read_unlock(void)
{
- debug_yield_read();
- barrier();
- debug_yield_read();
+ reader_barrier();
/*
* Finish using rcu before decrementing the pointer.
* See force_mb_all_threads().
*/
- urcu_active_readers[*urcu_parity]--;
- debug_yield_read();
+ urcu_active_readers -= RCU_GP_COUNT;
}
-extern void *urcu_publish_content(void **ptr, void *new);
+/**
+ * rcu_assign_pointer - assign (publicize) a pointer to a newly
+ * initialized structure that will be dereferenced by RCU read-side
+ * critical sections. Returns the value assigned.
+ *
+ * Inserts memory barriers on architectures that require them
+ * (pretty much all of them other than x86), and also prevents
+ * the compiler from reordering the code that initializes the
+ * structure after the pointer assignment. More importantly, this
+ * call documents which pointers will be dereferenced by RCU read-side
+ * code.
+ */
+
+#define rcu_assign_pointer(p, v) \
+ ({ \
+ if (!__builtin_constant_p(v) || \
+ ((v) != NULL)) \
+ wmb(); \
+ (p) = (v); \
+ smp_wmc(); \
+ })
+
+#define rcu_xchg_pointer(p, v) \
+ ({ \
+ if (!__builtin_constant_p(v) || \
+ ((v) != NULL)) \
+ wmb(); \
+ xchg(p, v); \
+ })
+
+extern void synchronize_rcu(void);
+
+/*
+ * Exchanges the pointer and waits for quiescent state.
+ * The pointer returned can be freed.
+ */
+#define urcu_publish_content(p, v) \
+ ({ \
+ void *oldptr; \
+ oldptr = rcu_xchg_pointer(p, v); \
+ synchronize_rcu(); \
+ oldptr; \
+ })
/*
* Reader thread registration.
projects / urcu.git / blobdiff