diff options
| -rw-r--r-- | include/linux/srcutree.h | 4 | ||||
| -rw-r--r-- | kernel/rcu/srcutree.c | 44 |
2 files changed, 42 insertions, 6 deletions
diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h index 1b9ff4ed37e4..e3014319d1ad 100644 --- a/include/linux/srcutree.h +++ b/include/linux/srcutree.h @@ -71,9 +71,11 @@ struct srcu_struct { 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 #. */ @@ -83,6 +85,8 @@ struct srcu_struct { 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; }; diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index 862008c147b0..6dd44e759f12 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -511,7 +511,10 @@ static bool srcu_readers_active(struct srcu_struct *ssp) 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 @@ -519,9 +522,18 @@ static bool srcu_readers_active(struct srcu_struct *ssp) */ 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; } /** @@ -623,6 +635,8 @@ static void srcu_gp_start(struct srcu_struct *ssp) (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); @@ -706,7 +720,7 @@ static void srcu_gp_end(struct srcu_struct *ssp) 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); @@ -893,7 +907,7 @@ static void srcu_funnel_gp_start(struct srcu_struct *ssp, struct srcu_data *sdp, // 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); } @@ -1448,6 +1462,7 @@ static void srcu_advance_state(struct srcu_struct *ssp) 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); } @@ -1462,6 +1477,7 @@ static void srcu_advance_state(struct srcu_struct *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. */ } } @@ -1552,12 +1568,28 @@ static void srcu_reschedule(struct srcu_struct *ssp, unsigned long delay) */ 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, |