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rcu: Make ->dynticks_nesting be a simple counter

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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 2017-10-03 14:43:40 -07:00
parent 58721f5da4
commit 51a1fd30f1
3 changed files with 21 additions and 47 deletions
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27
kernel/rcu/rcu.h
View File

@ -30,32 +30,7 @@
#define RCU_TRACE(stmt) #define RCU_TRACE(stmt)
#endif /* #else #ifdef CONFIG_RCU_TRACE */ #endif /* #else #ifdef CONFIG_RCU_TRACE */
/* /* Offset to allow for unmatched rcu_irq_{enter,exit}(). */
* Process-level increment to ->dynticks_nesting field. This allows for
* architectures that use half-interrupts and half-exceptions from
* process context.
*
* DYNTICK_TASK_NEST_MASK defines a field of width DYNTICK_TASK_NEST_WIDTH
* that counts the number of process-based reasons why RCU cannot
* consider the corresponding CPU to be idle, and DYNTICK_TASK_NEST_VALUE
* is the value used to increment or decrement this field.
*
* The rest of the bits could in principle be used to count interrupts,
* but this would mean that a negative-one value in the interrupt
* field could incorrectly zero out the DYNTICK_TASK_NEST_MASK field.
* We therefore provide a two-bit guard field defined by DYNTICK_TASK_MASK
* that is set to DYNTICK_TASK_FLAG upon initial exit from idle.
* The DYNTICK_TASK_EXIT_IDLE value is thus the combined value used upon
* initial exit from idle.
*/
#define DYNTICK_TASK_NEST_WIDTH 7
#define DYNTICK_TASK_NEST_VALUE ((LLONG_MAX >> DYNTICK_TASK_NEST_WIDTH) + 1)
#define DYNTICK_TASK_NEST_MASK (LLONG_MAX - DYNTICK_TASK_NEST_VALUE + 1)
#define DYNTICK_TASK_FLAG ((DYNTICK_TASK_NEST_VALUE / 8) * 2)
#define DYNTICK_TASK_MASK ((DYNTICK_TASK_NEST_VALUE / 8) * 3)
#define DYNTICK_TASK_EXIT_IDLE (DYNTICK_TASK_NEST_VALUE + \
DYNTICK_TASK_FLAG)
#define DYNTICK_IRQ_NONIDLE ((INT_MAX / 2) + 1) #define DYNTICK_IRQ_NONIDLE ((INT_MAX / 2) + 1)

40
kernel/rcu/tree.c
View File

@ -265,7 +265,7 @@ void rcu_bh_qs(void)
#endif #endif
static DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = { static DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
.dynticks_nesting = DYNTICK_TASK_EXIT_IDLE, .dynticks_nesting = 1,
.dynticks_nmi_nesting = DYNTICK_IRQ_NONIDLE, .dynticks_nmi_nesting = DYNTICK_IRQ_NONIDLE,
.dynticks = ATOMIC_INIT(RCU_DYNTICK_CTRL_CTR), .dynticks = ATOMIC_INIT(RCU_DYNTICK_CTRL_CTR),
}; };
@ -813,6 +813,10 @@ static void rcu_eqs_enter_common(bool user)
/* /*
* Enter an RCU extended quiescent state, which can be either the * Enter an RCU extended quiescent state, which can be either the
* idle loop or adaptive-tickless usermode execution. * idle loop or adaptive-tickless usermode execution.
*
* We crowbar the ->dynticks_nmi_nesting field to zero to allow for
* the possibility of usermode upcalls having messed up our count
* of interrupt nesting level during the prior busy period.
*/ */
static void rcu_eqs_enter(bool user) static void rcu_eqs_enter(bool user)
{ {
@ -821,11 +825,11 @@ static void rcu_eqs_enter(bool user)
rdtp = this_cpu_ptr(&rcu_dynticks); rdtp = this_cpu_ptr(&rcu_dynticks);
WRITE_ONCE(rdtp->dynticks_nmi_nesting, 0); WRITE_ONCE(rdtp->dynticks_nmi_nesting, 0);
WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
(rdtp->dynticks_nesting & DYNTICK_TASK_NEST_MASK) == 0); rdtp->dynticks_nesting == 0);
if ((rdtp->dynticks_nesting & DYNTICK_TASK_NEST_MASK) == DYNTICK_TASK_NEST_VALUE) if (rdtp->dynticks_nesting == 1)
rcu_eqs_enter_common(user); rcu_eqs_enter_common(user);
else else
rdtp->dynticks_nesting -= DYNTICK_TASK_NEST_VALUE; rdtp->dynticks_nesting--;
} }
/** /**
@ -836,10 +840,6 @@ static void rcu_eqs_enter(bool user)
* critical sections can occur in irq handlers in idle, a possibility * critical sections can occur in irq handlers in idle, a possibility
* handled by irq_enter() and irq_exit().) * handled by irq_enter() and irq_exit().)
* *
* We crowbar the ->dynticks_nesting field to zero to allow for
* the possibility of usermode upcalls having messed up our count
* of interrupt nesting level during the prior busy period.
*
* If you add or remove a call to rcu_idle_enter(), be sure to test with * If you add or remove a call to rcu_idle_enter(), be sure to test with
* CONFIG_RCU_EQS_DEBUG=y. * CONFIG_RCU_EQS_DEBUG=y.
*/ */
@ -984,6 +984,10 @@ static void rcu_eqs_exit_common(long long newval, int user)
/* /*
* Exit an RCU extended quiescent state, which can be either the * Exit an RCU extended quiescent state, which can be either the
* idle loop or adaptive-tickless usermode execution. * idle loop or adaptive-tickless usermode execution.
*
* We crowbar the ->dynticks_nmi_nesting field to DYNTICK_IRQ_NONIDLE to
* allow for the possibility of usermode upcalls messing up our count of
* interrupt nesting level during the busy period that is just now starting.
*/ */
static void rcu_eqs_exit(bool user) static void rcu_eqs_exit(bool user)
{ {
@ -994,12 +998,12 @@ static void rcu_eqs_exit(bool user)
rdtp = this_cpu_ptr(&rcu_dynticks); rdtp = this_cpu_ptr(&rcu_dynticks);
oldval = rdtp->dynticks_nesting; oldval = rdtp->dynticks_nesting;
WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && oldval < 0); WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && oldval < 0);
if (oldval & DYNTICK_TASK_NEST_MASK) { if (oldval) {
rdtp->dynticks_nesting += DYNTICK_TASK_NEST_VALUE; rdtp->dynticks_nesting++;
} else { } else {
__this_cpu_inc(disable_rcu_irq_enter); __this_cpu_inc(disable_rcu_irq_enter);
rcu_eqs_exit_common(DYNTICK_TASK_EXIT_IDLE, user); rcu_eqs_exit_common(1, user);
rdtp->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE; rdtp->dynticks_nesting = 1;
__this_cpu_dec(disable_rcu_irq_enter); __this_cpu_dec(disable_rcu_irq_enter);
WRITE_ONCE(rdtp->dynticks_nmi_nesting, DYNTICK_IRQ_NONIDLE); WRITE_ONCE(rdtp->dynticks_nmi_nesting, DYNTICK_IRQ_NONIDLE);
} }
@ -1011,11 +1015,6 @@ static void rcu_eqs_exit(bool user)
* Exit idle mode, in other words, -enter- the mode in which RCU * Exit idle mode, in other words, -enter- the mode in which RCU
* read-side critical sections can occur. * read-side critical sections can occur.
* *
* We crowbar the ->dynticks_nesting field to DYNTICK_TASK_NEST to
* allow for the possibility of usermode upcalls messing up our count
* of interrupt nesting level during the busy period that is just
* now starting.
*
* If you add or remove a call to rcu_idle_exit(), be sure to test with * If you add or remove a call to rcu_idle_exit(), be sure to test with
* CONFIG_RCU_EQS_DEBUG=y. * CONFIG_RCU_EQS_DEBUG=y.
*/ */
@ -1219,7 +1218,8 @@ EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online);
*/ */
static int rcu_is_cpu_rrupt_from_idle(void) static int rcu_is_cpu_rrupt_from_idle(void)
{ {
return __this_cpu_read(rcu_dynticks.dynticks_nesting) <= 1; return __this_cpu_read(rcu_dynticks.dynticks_nesting) <= 0 &&
__this_cpu_read(rcu_dynticks.dynticks_nmi_nesting) <= 1;
} }
/* /*
@ -3709,7 +3709,7 @@ rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
raw_spin_lock_irqsave_rcu_node(rnp, flags); raw_spin_lock_irqsave_rcu_node(rnp, flags);
rdp->grpmask = leaf_node_cpu_bit(rdp->mynode, cpu); rdp->grpmask = leaf_node_cpu_bit(rdp->mynode, cpu);
rdp->dynticks = &per_cpu(rcu_dynticks, cpu); rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_EXIT_IDLE); WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != 1);
WARN_ON_ONCE(rcu_dynticks_in_eqs(rcu_dynticks_snap(rdp->dynticks))); WARN_ON_ONCE(rcu_dynticks_in_eqs(rcu_dynticks_snap(rdp->dynticks)));
rdp->cpu = cpu; rdp->cpu = cpu;
rdp->rsp = rsp; rdp->rsp = rsp;
@ -3738,7 +3738,7 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp)
if (rcu_segcblist_empty(&rdp->cblist) && /* No early-boot CBs? */ if (rcu_segcblist_empty(&rdp->cblist) && /* No early-boot CBs? */
!init_nocb_callback_list(rdp)) !init_nocb_callback_list(rdp))
rcu_segcblist_init(&rdp->cblist); /* Re-enable callbacks. */ rcu_segcblist_init(&rdp->cblist); /* Re-enable callbacks. */
rdp->dynticks->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE; rdp->dynticks->dynticks_nesting = 1;
rcu_dynticks_eqs_online(); rcu_dynticks_eqs_online();
raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */ raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */

1
kernel/rcu/tree.h
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@ -39,7 +39,6 @@
*/ */
struct rcu_dynticks { struct rcu_dynticks {
long long dynticks_nesting; /* Track irq/process nesting level. */ long long dynticks_nesting; /* Track irq/process nesting level. */
/* Process level is worth LLONG_MAX/2. */
int dynticks_nmi_nesting; /* Track NMI nesting level. */ int dynticks_nmi_nesting; /* Track NMI nesting level. */
atomic_t dynticks; /* Even value for idle, else odd. */ atomic_t dynticks; /* Even value for idle, else odd. */
bool rcu_need_heavy_qs; /* GP old, need heavy quiescent state. */ bool rcu_need_heavy_qs; /* GP old, need heavy quiescent state. */