unsigned long srcu_gp_seq; /* Grace-period seq #. */
unsigned long srcu_gp_seq_needed; /* Latest gp_seq needed. */
unsigned long srcu_gp_seq_needed_exp; /* Furthest future exp GP. */
+ unsigned long srcu_gp_start; /* Last GP start timestamp (jiffies) */
unsigned long srcu_last_gp_end; /* Last GP end timestamp (ns) */
unsigned long srcu_size_jiffies; /* Current contention-measurement interval. */
unsigned long srcu_n_lock_retries; /* Contention events in current interval. */
+ unsigned long srcu_n_exp_nodelay; /* # expedited no-delays in current GP phase. */
struct srcu_data __percpu *sda; /* Per-CPU srcu_data array. */
bool sda_is_static; /* May ->sda be passed to free_percpu()? */
unsigned long srcu_barrier_seq; /* srcu_barrier seq #. */
atomic_t srcu_barrier_cpu_cnt; /* # CPUs not yet posting a */
/* callback for the barrier */
/* operation. */
+ unsigned long reschedule_jiffies;
+ unsigned long reschedule_count;
struct delayed_work work;
struct lockdep_map dep_map;
};
return sum;
}
-#define SRCU_INTERVAL 1
+#define SRCU_INTERVAL 1 // Base delay if no expedited GPs pending.
+#define SRCU_MAX_INTERVAL 10 // Maximum incremental delay from slow readers.
+#define SRCU_MAX_NODELAY_PHASE 1 // Maximum per-GP-phase consecutive no-delay instances.
+#define SRCU_MAX_NODELAY 100 // Maximum consecutive no-delay instances.
/*
* Return grace-period delay, zero if there are expedited grace
*/
static unsigned long srcu_get_delay(struct srcu_struct *ssp)
{
+ unsigned long jbase = SRCU_INTERVAL;
+
if (ULONG_CMP_LT(READ_ONCE(ssp->srcu_gp_seq), READ_ONCE(ssp->srcu_gp_seq_needed_exp)))
- return 0;
- return SRCU_INTERVAL;
+ jbase = 0;
+ if (rcu_seq_state(READ_ONCE(ssp->srcu_gp_seq)))
+ jbase += jiffies - READ_ONCE(ssp->srcu_gp_start);
+ if (!jbase) {
+ WRITE_ONCE(ssp->srcu_n_exp_nodelay, READ_ONCE(ssp->srcu_n_exp_nodelay) + 1);
+ if (READ_ONCE(ssp->srcu_n_exp_nodelay) > SRCU_MAX_NODELAY_PHASE)
+ jbase = 1;
+ }
+ return jbase > SRCU_MAX_INTERVAL ? SRCU_MAX_INTERVAL : jbase;
}
/**
(void)rcu_segcblist_accelerate(&sdp->srcu_cblist,
rcu_seq_snap(&ssp->srcu_gp_seq));
spin_unlock_rcu_node(sdp); /* Interrupts remain disabled. */
+ WRITE_ONCE(ssp->srcu_gp_start, jiffies);
+ WRITE_ONCE(ssp->srcu_n_exp_nodelay, 0);
smp_mb(); /* Order prior store to ->srcu_gp_seq_needed vs. GP start. */
rcu_seq_start(&ssp->srcu_gp_seq);
state = rcu_seq_state(ssp->srcu_gp_seq);
spin_lock_irq_rcu_node(ssp);
idx = rcu_seq_state(ssp->srcu_gp_seq);
WARN_ON_ONCE(idx != SRCU_STATE_SCAN2);
- cbdelay = srcu_get_delay(ssp);
+ cbdelay = !!srcu_get_delay(ssp);
WRITE_ONCE(ssp->srcu_last_gp_end, ktime_get_mono_fast_ns());
rcu_seq_end(&ssp->srcu_gp_seq);
gpseq = rcu_seq_current(&ssp->srcu_gp_seq);
// the one boot CPU running with interrupts still disabled.
if (likely(srcu_init_done))
queue_delayed_work(rcu_gp_wq, &ssp->work,
- srcu_get_delay(ssp));
+ !!srcu_get_delay(ssp));
else if (list_empty(&ssp->work.work.entry))
list_add(&ssp->work.work.entry, &srcu_boot_list);
}
srcu_flip(ssp);
spin_lock_irq_rcu_node(ssp);
rcu_seq_set_state(&ssp->srcu_gp_seq, SRCU_STATE_SCAN2);
+ ssp->srcu_n_exp_nodelay = 0;
spin_unlock_irq_rcu_node(ssp);
}
mutex_unlock(&ssp->srcu_gp_mutex);
return; /* readers present, retry later. */
}
+ ssp->srcu_n_exp_nodelay = 0;
srcu_gp_end(ssp); /* Releases ->srcu_gp_mutex. */
}
}
*/
static void process_srcu(struct work_struct *work)
{
+ unsigned long curdelay;
+ unsigned long j;
struct srcu_struct *ssp;
ssp = container_of(work, struct srcu_struct, work.work);
srcu_advance_state(ssp);
- srcu_reschedule(ssp, srcu_get_delay(ssp));
+ curdelay = srcu_get_delay(ssp);
+ if (curdelay) {
+ WRITE_ONCE(ssp->reschedule_count, 0);
+ } else {
+ j = jiffies;
+ if (READ_ONCE(ssp->reschedule_jiffies) == j) {
+ WRITE_ONCE(ssp->reschedule_count, READ_ONCE(ssp->reschedule_count) + 1);
+ if (READ_ONCE(ssp->reschedule_count) > SRCU_MAX_NODELAY)
+ curdelay = 1;
+ } else {
+ WRITE_ONCE(ssp->reschedule_count, 1);
+ WRITE_ONCE(ssp->reschedule_jiffies, j);
+ }
+ }
+ srcu_reschedule(ssp, curdelay);
}
void srcutorture_get_gp_data(enum rcutorture_type test_type,