rcu: Make ->dynticks_nesting be a simple counter
Now that ->dynticks_nesting counts only process-level dyntick-idle entry and exit, there is no need for the elaborate segmented counter with its guard fields and overflow checking. This commit therefore makes ->dynticks_nesting be a simple counter. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney
parent
58721f5da4
commit
51a1fd30f1
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@ -30,32 +30,7 @@
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#define RCU_TRACE(stmt)
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#endif /* #else #ifdef CONFIG_RCU_TRACE */
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/*
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* Process-level increment to ->dynticks_nesting field. This allows for
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* architectures that use half-interrupts and half-exceptions from
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* process context.
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*
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* DYNTICK_TASK_NEST_MASK defines a field of width DYNTICK_TASK_NEST_WIDTH
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* that counts the number of process-based reasons why RCU cannot
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* consider the corresponding CPU to be idle, and DYNTICK_TASK_NEST_VALUE
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* is the value used to increment or decrement this field.
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*
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* The rest of the bits could in principle be used to count interrupts,
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* but this would mean that a negative-one value in the interrupt
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* field could incorrectly zero out the DYNTICK_TASK_NEST_MASK field.
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* We therefore provide a two-bit guard field defined by DYNTICK_TASK_MASK
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* that is set to DYNTICK_TASK_FLAG upon initial exit from idle.
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* The DYNTICK_TASK_EXIT_IDLE value is thus the combined value used upon
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* initial exit from idle.
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*/
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#define DYNTICK_TASK_NEST_WIDTH 7
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#define DYNTICK_TASK_NEST_VALUE ((LLONG_MAX >> DYNTICK_TASK_NEST_WIDTH) + 1)
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#define DYNTICK_TASK_NEST_MASK (LLONG_MAX - DYNTICK_TASK_NEST_VALUE + 1)
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#define DYNTICK_TASK_FLAG ((DYNTICK_TASK_NEST_VALUE / 8) * 2)
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#define DYNTICK_TASK_MASK ((DYNTICK_TASK_NEST_VALUE / 8) * 3)
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#define DYNTICK_TASK_EXIT_IDLE (DYNTICK_TASK_NEST_VALUE + \
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DYNTICK_TASK_FLAG)
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/* Offset to allow for unmatched rcu_irq_{enter,exit}(). */
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#define DYNTICK_IRQ_NONIDLE ((INT_MAX / 2) + 1)
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@ -265,7 +265,7 @@ void rcu_bh_qs(void)
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#endif
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static DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
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.dynticks_nesting = DYNTICK_TASK_EXIT_IDLE,
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.dynticks_nesting = 1,
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.dynticks_nmi_nesting = DYNTICK_IRQ_NONIDLE,
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.dynticks = ATOMIC_INIT(RCU_DYNTICK_CTRL_CTR),
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};
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@ -813,6 +813,10 @@ static void rcu_eqs_enter_common(bool user)
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/*
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* Enter an RCU extended quiescent state, which can be either the
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* idle loop or adaptive-tickless usermode execution.
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*
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* We crowbar the ->dynticks_nmi_nesting field to zero to allow for
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* the possibility of usermode upcalls having messed up our count
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* of interrupt nesting level during the prior busy period.
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*/
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static void rcu_eqs_enter(bool user)
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{
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@ -821,11 +825,11 @@ static void rcu_eqs_enter(bool user)
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rdtp = this_cpu_ptr(&rcu_dynticks);
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WRITE_ONCE(rdtp->dynticks_nmi_nesting, 0);
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WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
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(rdtp->dynticks_nesting & DYNTICK_TASK_NEST_MASK) == 0);
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if ((rdtp->dynticks_nesting & DYNTICK_TASK_NEST_MASK) == DYNTICK_TASK_NEST_VALUE)
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rdtp->dynticks_nesting == 0);
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if (rdtp->dynticks_nesting == 1)
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rcu_eqs_enter_common(user);
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else
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rdtp->dynticks_nesting -= DYNTICK_TASK_NEST_VALUE;
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rdtp->dynticks_nesting--;
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}
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/**
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@ -836,10 +840,6 @@ static void rcu_eqs_enter(bool user)
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* critical sections can occur in irq handlers in idle, a possibility
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* handled by irq_enter() and irq_exit().)
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*
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* We crowbar the ->dynticks_nesting field to zero to allow for
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* the possibility of usermode upcalls having messed up our count
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* of interrupt nesting level during the prior busy period.
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*
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* If you add or remove a call to rcu_idle_enter(), be sure to test with
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* CONFIG_RCU_EQS_DEBUG=y.
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*/
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@ -984,6 +984,10 @@ static void rcu_eqs_exit_common(long long newval, int user)
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/*
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* Exit an RCU extended quiescent state, which can be either the
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* idle loop or adaptive-tickless usermode execution.
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*
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* We crowbar the ->dynticks_nmi_nesting field to DYNTICK_IRQ_NONIDLE to
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* allow for the possibility of usermode upcalls messing up our count of
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* interrupt nesting level during the busy period that is just now starting.
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*/
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static void rcu_eqs_exit(bool user)
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{
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@ -994,12 +998,12 @@ static void rcu_eqs_exit(bool user)
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rdtp = this_cpu_ptr(&rcu_dynticks);
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oldval = rdtp->dynticks_nesting;
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WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && oldval < 0);
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if (oldval & DYNTICK_TASK_NEST_MASK) {
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rdtp->dynticks_nesting += DYNTICK_TASK_NEST_VALUE;
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if (oldval) {
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rdtp->dynticks_nesting++;
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} else {
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__this_cpu_inc(disable_rcu_irq_enter);
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rcu_eqs_exit_common(DYNTICK_TASK_EXIT_IDLE, user);
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rdtp->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
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rcu_eqs_exit_common(1, user);
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rdtp->dynticks_nesting = 1;
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__this_cpu_dec(disable_rcu_irq_enter);
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WRITE_ONCE(rdtp->dynticks_nmi_nesting, DYNTICK_IRQ_NONIDLE);
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}
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@ -1011,11 +1015,6 @@ static void rcu_eqs_exit(bool user)
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* Exit idle mode, in other words, -enter- the mode in which RCU
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* read-side critical sections can occur.
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*
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* We crowbar the ->dynticks_nesting field to DYNTICK_TASK_NEST to
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* allow for the possibility of usermode upcalls messing up our count
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* of interrupt nesting level during the busy period that is just
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* now starting.
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*
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* If you add or remove a call to rcu_idle_exit(), be sure to test with
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* CONFIG_RCU_EQS_DEBUG=y.
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*/
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@ -1219,7 +1218,8 @@ EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online);
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*/
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static int rcu_is_cpu_rrupt_from_idle(void)
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{
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return __this_cpu_read(rcu_dynticks.dynticks_nesting) <= 1;
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return __this_cpu_read(rcu_dynticks.dynticks_nesting) <= 0 &&
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__this_cpu_read(rcu_dynticks.dynticks_nmi_nesting) <= 1;
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}
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/*
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@ -3709,7 +3709,7 @@ rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
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raw_spin_lock_irqsave_rcu_node(rnp, flags);
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rdp->grpmask = leaf_node_cpu_bit(rdp->mynode, cpu);
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rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
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WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_EXIT_IDLE);
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WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != 1);
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WARN_ON_ONCE(rcu_dynticks_in_eqs(rcu_dynticks_snap(rdp->dynticks)));
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rdp->cpu = cpu;
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rdp->rsp = rsp;
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@ -3738,7 +3738,7 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp)
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if (rcu_segcblist_empty(&rdp->cblist) && /* No early-boot CBs? */
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!init_nocb_callback_list(rdp))
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rcu_segcblist_init(&rdp->cblist); /* Re-enable callbacks. */
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rdp->dynticks->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
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rdp->dynticks->dynticks_nesting = 1;
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rcu_dynticks_eqs_online();
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raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
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@ -39,7 +39,6 @@
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*/
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struct rcu_dynticks {
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long long dynticks_nesting; /* Track irq/process nesting level. */
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/* Process level is worth LLONG_MAX/2. */
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int dynticks_nmi_nesting; /* Track NMI nesting level. */
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atomic_t dynticks; /* Even value for idle, else odd. */
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bool rcu_need_heavy_qs; /* GP old, need heavy quiescent state. */
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