diff options
Diffstat (limited to 'kernel/rcu')
| -rw-r--r-- | kernel/rcu/tree.c | 52 | ||||
| -rw-r--r-- | kernel/rcu/tree.h | 3 | ||||
| -rw-r--r-- | kernel/rcu/tree_plugin.h | 5 |
3 files changed, 15 insertions, 45 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 77d2cbf7c831..bc42c600027c 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1018,25 +1018,6 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp) return 1; } - /* - * Has this CPU encountered a cond_resched() since the beginning - * of the grace period? For this to be the case, the CPU has to - * have noticed the current grace period. This might not be the - * case for nohz_full CPUs looping in the kernel. - */ - jtsq = jiffies_till_sched_qs; - ruqp = per_cpu_ptr(&rcu_dynticks.rcu_urgent_qs, rdp->cpu); - if (time_after(jiffies, rcu_state.gp_start + jtsq) && - READ_ONCE(rdp->rcu_qs_ctr_snap) != per_cpu(rcu_dynticks.rcu_qs_ctr, rdp->cpu) && - rcu_seq_current(&rdp->gp_seq) == rnp->gp_seq && !rdp->gpwrap) { - trace_rcu_fqs(rcu_state.name, rdp->gp_seq, rdp->cpu, TPS("rqc")); - rcu_gpnum_ovf(rnp, rdp); - return 1; - } else if (time_after(jiffies, rcu_state.gp_start + jtsq)) { - /* Load rcu_qs_ctr before store to rcu_urgent_qs. */ - smp_store_release(ruqp, true); - } - /* If waiting too long on an offline CPU, complain. */ if (!(rdp->grpmask & rcu_rnp_online_cpus(rnp)) && time_after(jiffies, rcu_state.gp_start + HZ)) { @@ -1060,29 +1041,27 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp) /* * A CPU running for an extended time within the kernel can - * delay RCU grace periods. When the CPU is in NO_HZ_FULL mode, - * even context-switching back and forth between a pair of - * in-kernel CPU-bound tasks cannot advance grace periods. - * So if the grace period is old enough, make the CPU pay attention. - * Note that the unsynchronized assignments to the per-CPU - * rcu_need_heavy_qs variable are safe. Yes, setting of - * bits can be lost, but they will be set again on the next - * force-quiescent-state pass. So lost bit sets do not result - * in incorrect behavior, merely in a grace period lasting - * a few jiffies longer than it might otherwise. Because - * there are at most four threads involved, and because the - * updates are only once every few jiffies, the probability of - * lossage (and thus of slight grace-period extension) is - * quite low. + * delay RCU grace periods: (1) At age jiffies_till_sched_qs, + * set .rcu_urgent_qs, (2) At age 2*jiffies_till_sched_qs, set + * both .rcu_need_heavy_qs and .rcu_urgent_qs. Note that the + * unsynchronized assignments to the per-CPU rcu_need_heavy_qs + * variable are safe because the assignments are repeated if this + * CPU failed to pass through a quiescent state. This code + * also checks .jiffies_resched in case jiffies_till_sched_qs + * is set way high. */ + jtsq = jiffies_till_sched_qs; + ruqp = per_cpu_ptr(&rcu_dynticks.rcu_urgent_qs, rdp->cpu); rnhqp = &per_cpu(rcu_dynticks.rcu_need_heavy_qs, rdp->cpu); if (!READ_ONCE(*rnhqp) && - (time_after(jiffies, rcu_state.gp_start + jtsq) || + (time_after(jiffies, rcu_state.gp_start + jtsq * 2) || time_after(jiffies, rcu_state.jiffies_resched))) { WRITE_ONCE(*rnhqp, true); /* Store rcu_need_heavy_qs before rcu_urgent_qs. */ smp_store_release(ruqp, true); rcu_state.jiffies_resched += jtsq; /* Re-enable beating. */ + } else if (time_after(jiffies, rcu_state.gp_start + jtsq)) { + WRITE_ONCE(*ruqp, true); } /* @@ -1091,7 +1070,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp) * see if the CPU is getting hammered with interrupts, but only * once per grace period, just to keep the IPIs down to a dull roar. */ - if (jiffies - rcu_state.gp_start > rcu_jiffies_till_stall_check() / 2) { + if (time_after(jiffies, rcu_state.jiffies_resched)) { resched_cpu(rdp->cpu); if (IS_ENABLED(CONFIG_IRQ_WORK) && !rdp->rcu_iw_pending && rdp->rcu_iw_gp_seq != rnp->gp_seq && @@ -1669,7 +1648,6 @@ static bool __note_gp_changes(struct rcu_node *rnp, struct rcu_data *rdp) trace_rcu_grace_period(rcu_state.name, rnp->gp_seq, TPS("cpustart")); need_gp = !!(rnp->qsmask & rdp->grpmask); rdp->cpu_no_qs.b.norm = need_gp; - rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_dynticks.rcu_qs_ctr); rdp->core_needs_qs = need_gp; zero_cpu_stall_ticks(rdp); } @@ -2230,7 +2208,6 @@ rcu_report_qs_rdp(int cpu, struct rcu_data *rdp) * within the current grace period. */ rdp->cpu_no_qs.b.norm = true; /* need qs for new gp. */ - rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_dynticks.rcu_qs_ctr); raw_spin_unlock_irqrestore_rcu_node(rnp, flags); return; } @@ -3213,7 +3190,6 @@ int rcutree_prepare_cpu(unsigned int cpu) rdp->gp_seq = rnp->gp_seq; rdp->gp_seq_needed = rnp->gp_seq; rdp->cpu_no_qs.b.norm = true; - rdp->rcu_qs_ctr_snap = per_cpu(rcu_dynticks.rcu_qs_ctr, cpu); rdp->core_needs_qs = false; rdp->rcu_iw_pending = false; rdp->rcu_iw_gp_seq = rnp->gp_seq - 1; diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index 8cf93ac277ec..4866fa44ab0b 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -42,7 +42,6 @@ struct rcu_dynticks { long dynticks_nmi_nesting; /* Track irq/NMI nesting level. */ atomic_t dynticks; /* Even value for idle, else odd. */ bool rcu_need_heavy_qs; /* GP old, need heavy quiescent state. */ - unsigned long rcu_qs_ctr; /* Light universal quiescent state ctr. */ bool rcu_urgent_qs; /* GP old need light quiescent state. */ #ifdef CONFIG_RCU_FAST_NO_HZ bool all_lazy; /* Are all CPU's CBs lazy? */ @@ -188,8 +187,6 @@ struct rcu_data { /* 1) quiescent-state and grace-period handling : */ unsigned long gp_seq; /* Track rsp->rcu_gp_seq counter. */ unsigned long gp_seq_needed; /* Track rsp->rcu_gp_seq_needed ctr. */ - unsigned long rcu_qs_ctr_snap;/* Snapshot of rcu_qs_ctr to check */ - /* for rcu_all_qs() invocations. */ union rcu_noqs cpu_no_qs; /* No QSes yet for this CPU. */ bool core_needs_qs; /* Core waits for quiesc state. */ bool beenonline; /* CPU online at least once. */ diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index beaaca7a11f4..726d57708849 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -978,9 +978,7 @@ void rcu_all_qs(void) rcu_momentary_dyntick_idle(); local_irq_restore(flags); } - if (unlikely(raw_cpu_read(rcu_data.cpu_no_qs.b.exp))) - rcu_qs(); - this_cpu_inc(rcu_dynticks.rcu_qs_ctr); + rcu_qs(); barrier(); /* Avoid RCU read-side critical sections leaking up. */ preempt_enable(); } @@ -1000,7 +998,6 @@ void rcu_note_context_switch(bool preempt) this_cpu_write(rcu_dynticks.rcu_urgent_qs, false); if (unlikely(raw_cpu_read(rcu_dynticks.rcu_need_heavy_qs))) rcu_momentary_dyntick_idle(); - this_cpu_inc(rcu_dynticks.rcu_qs_ctr); if (!preempt) rcu_tasks_qs(current); out: |