#include <pthread.h>
#include <stdbool.h>
#include <poll.h>
-#include <side/trace.h>
#include <rseq/rseq.h>
+#include <linux/futex.h>
+#include <sys/time.h>
+#include <unistd.h>
+#include <sys/syscall.h>
+#include <side/macros.h>
#define SIDE_CACHE_LINE_SIZE 256
uintptr_t rseq_begin;
uintptr_t end;
uintptr_t rseq_end;
-} __attribute__((__aligned__(SIDE_CACHE_LINE_SIZE)));
+};
struct side_rcu_cpu_gp_state {
struct side_rcu_percpu_count count[2];
-};
+} __attribute__((__aligned__(SIDE_CACHE_LINE_SIZE)));
struct side_rcu_gp_state {
struct side_rcu_cpu_gp_state *percpu_state;
int nr_cpus;
+ int32_t futex;
unsigned int period;
pthread_mutex_t gp_lock;
};
-//TODO: implement wait/wakeup for grace period using sys_futex
+struct side_rcu_read_state {
+ struct side_rcu_percpu_count *percpu_count;
+ int cpu;
+};
+
+extern unsigned int side_rcu_rseq_membarrier_available __attribute__((visibility("hidden")));
+
+static inline
+int futex(int32_t *uaddr, int op, int32_t val,
+ const struct timespec *timeout, int32_t *uaddr2, int32_t val3)
+{
+ return syscall(__NR_futex, uaddr, op, val, timeout, uaddr2, val3);
+}
+
+/*
+ * Wake-up side_rcu_wait_grace_period. Called concurrently from many
+ * threads.
+ */
+static inline
+void side_rcu_wake_up_gp(struct side_rcu_gp_state *gp_state)
+{
+ if (side_unlikely(__atomic_load_n(&gp_state->futex, __ATOMIC_RELAXED) == -1)) {
+ __atomic_store_n(&gp_state->futex, 0, __ATOMIC_RELAXED);
+ /* TODO: handle futex return values. */
+ (void) futex(&gp_state->futex, FUTEX_WAKE, 1, NULL, NULL, 0);
+ }
+}
+
static inline
-unsigned int side_rcu_read_begin(struct side_rcu_gp_state *gp_state)
+void side_rcu_read_begin(struct side_rcu_gp_state *gp_state, struct side_rcu_read_state *read_state)
{
- unsigned int period = __atomic_load_n(&gp_state->period, __ATOMIC_RELAXED);
+ struct side_rcu_percpu_count *begin_cpu_count;
struct side_rcu_cpu_gp_state *cpu_gp_state;
+ unsigned int period;
int cpu;
- if (side_likely(rseq_offset > 0)) {
- cpu = rseq_cpu_start();
- cpu_gp_state = &gp_state->percpu_state[cpu];
- if (!rseq_addv((intptr_t *)&cpu_gp_state->count[period].rseq_begin, 1, cpu))
- goto fence;
+ cpu = rseq_cpu_start();
+ period = __atomic_load_n(&gp_state->period, __ATOMIC_RELAXED);
+ cpu_gp_state = &gp_state->percpu_state[cpu];
+ read_state->percpu_count = begin_cpu_count = &cpu_gp_state->count[period];
+ read_state->cpu = cpu;
+ if (side_likely(side_rcu_rseq_membarrier_available &&
+ !rseq_addv(RSEQ_MO_RELAXED, RSEQ_PERCPU_CPU_ID,
+ (intptr_t *)&begin_cpu_count->rseq_begin, 1, cpu))) {
+ /*
+ * This compiler barrier (A) is paired with membarrier() at (C),
+ * (D), (E). It effectively upgrades this compiler barrier to a
+ * SEQ_CST fence with respect to the paired barriers.
+ *
+ * This barrier (A) ensures that the contents of the read-side
+ * critical section does not leak before the "begin" counter
+ * increment. It pairs with memory barriers (D) and (E).
+ *
+ * This barrier (A) also ensures that the "begin" increment is
+ * before the "end" increment. It pairs with memory barrier (C).
+ * It is redundant with barrier (B) for that purpose.
+ */
+ rseq_barrier();
+ return;
}
+ /* Fallback to atomic increment and SEQ_CST. */
cpu = sched_getcpu();
if (side_unlikely(cpu < 0))
cpu = 0;
+ read_state->cpu = cpu;
cpu_gp_state = &gp_state->percpu_state[cpu];
- (void) __atomic_add_fetch(&cpu_gp_state->count[period].begin, 1, __ATOMIC_RELAXED);
-fence:
- /*
- * This memory barrier (A) ensures that the contents of the
- * read-side critical section does not leak before the "begin"
- * counter increment. It pairs with memory barriers (D) and (E).
- *
- * This memory barrier (A) also ensures that the "begin"
- * increment is before the "end" increment. It pairs with memory
- * barrier (C). It is redundant with memory barrier (B) for that
- * purpose.
- */
- rseq_barrier();
- return period;
+ read_state->percpu_count = begin_cpu_count = &cpu_gp_state->count[period];
+ (void) __atomic_add_fetch(&begin_cpu_count->begin, 1, __ATOMIC_SEQ_CST);
}
static inline
-void side_rcu_read_end(struct side_rcu_gp_state *gp_state, unsigned int period)
+void side_rcu_read_end(struct side_rcu_gp_state *gp_state, struct side_rcu_read_state *read_state)
{
- struct side_rcu_cpu_gp_state *cpu_gp_state;
- int cpu;
+ struct side_rcu_percpu_count *begin_cpu_count = read_state->percpu_count;
+ int cpu = read_state->cpu;
/*
- * This memory barrier (B) ensures that the contents of the
- * read-side critical section does not leak after the "end"
- * counter increment. It pairs with memory barriers (D) and (E).
+ * This compiler barrier (B) is paired with membarrier() at (C),
+ * (D), (E). It effectively upgrades this compiler barrier to a
+ * SEQ_CST fence with respect to the paired barriers.
*
- * This memory barrier (B) also ensures that the "begin"
- * increment is before the "end" increment. It pairs with memory
- * barrier (C). It is redundant with memory barrier (A) for that
- * purpose.
+ * This barrier (B) ensures that the contents of the read-side
+ * critical section does not leak after the "end" counter
+ * increment. It pairs with memory barriers (D) and (E).
+ *
+ * This barrier (B) also ensures that the "begin" increment is
+ * before the "end" increment. It pairs with memory barrier (C).
+ * It is redundant with barrier (A) for that purpose.
*/
rseq_barrier();
-
- if (side_likely(rseq_offset > 0)) {
- cpu = rseq_cpu_start();
- cpu_gp_state = &gp_state->percpu_state[cpu];
- if (!rseq_addv((intptr_t *)&cpu_gp_state->count[period].rseq_end, 1, cpu))
- return;
+ if (side_likely(side_rcu_rseq_membarrier_available &&
+ !rseq_addv(RSEQ_MO_RELAXED, RSEQ_PERCPU_CPU_ID,
+ (intptr_t *)&begin_cpu_count->rseq_end, 1, cpu))) {
+ /*
+ * This barrier (F) is paired with membarrier()
+ * at (G). It orders increment of the begin/end
+ * counters before load/store to the futex.
+ */
+ rseq_barrier();
+ goto end;
}
- cpu = sched_getcpu();
- if (side_unlikely(cpu < 0))
- cpu = 0;
- cpu_gp_state = &gp_state->percpu_state[cpu];
- (void) __atomic_add_fetch(&cpu_gp_state->count[period].end, 1, __ATOMIC_RELAXED);
+ /* Fallback to atomic increment and SEQ_CST. */
+ (void) __atomic_add_fetch(&begin_cpu_count->end, 1, __ATOMIC_SEQ_CST);
+ /*
+ * This barrier (F) implied by SEQ_CST is paired with SEQ_CST
+ * barrier or membarrier() at (G). It orders increment of the
+ * begin/end counters before load/store to the futex.
+ */
+end:
+ side_rcu_wake_up_gp(gp_state);
}
#define side_rcu_dereference(p) \
(_____side_v); \
})
-#define side_rcu_assign_pointer(p, v) __atomic_store_n(&(p), v, __ATOMIC_RELEASE); \
+#define side_rcu_assign_pointer(p, v) __atomic_store_n(&(p), v, __ATOMIC_RELEASE);
void side_rcu_wait_grace_period(struct side_rcu_gp_state *gp_state) __attribute__((visibility("hidden")));
void side_rcu_gp_init(struct side_rcu_gp_state *rcu_gp) __attribute__((visibility("hidden")));
projects / libside.git / blobdiff