forked from luck/tmp_suning_uos_patched
rcu: Refactor rcu_{nmi,irq}_{enter,exit}()
When entering or exiting irq or NMI handlers, the current code uses ->dynticks_nmi_nesting to detect if it is in the outermost handler, that is, the one interrupting or returning to an RCU-idle context (the idle loop or nohz_full usermode execution). When entering the outermost handler via an interrupt (as opposed to NMI), it is necessary to invoke rcu_dynticks_task_exit() just before the CPU is marked non-idle from an RCU perspective and to invoke rcu_cleanup_after_idle() just after the CPU is marked non-idle. Similarly, when exiting the outermost handler via an interrupt, it is necessary to invoke rcu_prepare_for_idle() just before marking the CPU idle and to invoke rcu_dynticks_task_enter() just after marking the CPU idle. The decision to execute these four functions is currently taken in rcu_irq_enter() and rcu_irq_exit() as follows: rcu_irq_enter() /* A conditional branch with ->dynticks_nmi_nesting */ rcu_nmi_enter() /* A conditional branch with ->dynticks */ /* A conditional branch with ->dynticks_nmi_nesting */ rcu_irq_exit() /* A conditional branch with ->dynticks_nmi_nesting */ rcu_nmi_exit() /* A conditional branch with ->dynticks_nmi_nesting */ /* A conditional branch with ->dynticks_nmi_nesting */ rcu_nmi_enter() /* A conditional branch with ->dynticks */ rcu_nmi_exit() /* A conditional branch with ->dynticks_nmi_nesting */ This works, but the conditional branches in rcu_irq_enter() and rcu_irq_exit() are redundant with those in rcu_nmi_enter() and rcu_nmi_exit(), respectively. Redundant branches are not something we want in the to/from-idle fastpaths, so this commit refactors rcu_{nmi,irq}_{enter,exit}() so they use a common inlined function passed a constant argument as follows: rcu_irq_enter() inlining rcu_nmi_enter_common(irq=true) /* A conditional branch with ->dynticks */ rcu_irq_exit() inlining rcu_nmi_exit_common(irq=true) /* A conditional branch with ->dynticks_nmi_nesting */ rcu_nmi_enter() inlining rcu_nmi_enter_common(irq=false) /* A conditional branch with ->dynticks */ rcu_nmi_exit() inlining rcu_nmi_exit_common(irq=false) /* A conditional branch with ->dynticks_nmi_nesting */ The combination of the constant function argument and the inlining allows the compiler to discard the conditionals that previously controlled execution of rcu_dynticks_task_exit(), rcu_cleanup_after_idle(), rcu_prepare_for_idle(), and rcu_dynticks_task_enter(). This reduces both the to-idle and from-idle path lengths by two conditional branches each, and improves readability as well. This commit also changes order of execution from this: rcu_dynticks_task_exit(); rcu_dynticks_eqs_exit(); trace_rcu_dyntick(); rcu_cleanup_after_idle(); To this: rcu_dynticks_task_exit(); rcu_dynticks_eqs_exit(); rcu_cleanup_after_idle(); trace_rcu_dyntick(); In other words, the calls to rcu_cleanup_after_idle() and trace_rcu_dyntick() are reversed. This has no functional effect because the real concern is whether a given call is before or after the call to rcu_dynticks_eqs_exit(), and this patch does not change that. Before the call to rcu_dynticks_eqs_exit(), RCU is not yet watching the current CPU and after that call RCU is watching. A similar switch in calling order happens on the idle-entry path, with similar lack of effect for the same reasons. Suggested-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by: Byungchul Park <byungchul.park@lge.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> [ paulmck: Applied Steven Rostedt feedback. ] Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
This commit is contained in:
parent
5b394b2ddf
commit
cf7614e13c
|
@ -770,18 +770,16 @@ void rcu_user_enter(void)
|
|||
}
|
||||
#endif /* CONFIG_NO_HZ_FULL */
|
||||
|
||||
/**
|
||||
* rcu_nmi_exit - inform RCU of exit from NMI context
|
||||
*
|
||||
/*
|
||||
* If we are returning from the outermost NMI handler that interrupted an
|
||||
* RCU-idle period, update rdtp->dynticks and rdtp->dynticks_nmi_nesting
|
||||
* to let the RCU grace-period handling know that the CPU is back to
|
||||
* being RCU-idle.
|
||||
*
|
||||
* If you add or remove a call to rcu_nmi_exit(), be sure to test
|
||||
* If you add or remove a call to rcu_nmi_exit_common(), be sure to test
|
||||
* with CONFIG_RCU_EQS_DEBUG=y.
|
||||
*/
|
||||
void rcu_nmi_exit(void)
|
||||
static __always_inline void rcu_nmi_exit_common(bool irq)
|
||||
{
|
||||
struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
|
||||
|
||||
|
@ -807,7 +805,26 @@ void rcu_nmi_exit(void)
|
|||
/* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */
|
||||
trace_rcu_dyntick(TPS("Startirq"), rdtp->dynticks_nmi_nesting, 0, rdtp->dynticks);
|
||||
WRITE_ONCE(rdtp->dynticks_nmi_nesting, 0); /* Avoid store tearing. */
|
||||
|
||||
if (irq)
|
||||
rcu_prepare_for_idle();
|
||||
|
||||
rcu_dynticks_eqs_enter();
|
||||
|
||||
if (irq)
|
||||
rcu_dynticks_task_enter();
|
||||
}
|
||||
|
||||
/**
|
||||
* rcu_nmi_exit - inform RCU of exit from NMI context
|
||||
* @irq: Is this call from rcu_irq_exit?
|
||||
*
|
||||
* If you add or remove a call to rcu_nmi_exit(), be sure to test
|
||||
* with CONFIG_RCU_EQS_DEBUG=y.
|
||||
*/
|
||||
void rcu_nmi_exit(void)
|
||||
{
|
||||
rcu_nmi_exit_common(false);
|
||||
}
|
||||
|
||||
/**
|
||||
|
@ -831,14 +848,8 @@ void rcu_nmi_exit(void)
|
|||
*/
|
||||
void rcu_irq_exit(void)
|
||||
{
|
||||
struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
|
||||
|
||||
lockdep_assert_irqs_disabled();
|
||||
if (rdtp->dynticks_nmi_nesting == 1)
|
||||
rcu_prepare_for_idle();
|
||||
rcu_nmi_exit();
|
||||
if (rdtp->dynticks_nmi_nesting == 0)
|
||||
rcu_dynticks_task_enter();
|
||||
rcu_nmi_exit_common(true);
|
||||
}
|
||||
|
||||
/*
|
||||
|
@ -921,7 +932,8 @@ void rcu_user_exit(void)
|
|||
#endif /* CONFIG_NO_HZ_FULL */
|
||||
|
||||
/**
|
||||
* rcu_nmi_enter - inform RCU of entry to NMI context
|
||||
* rcu_nmi_enter_common - inform RCU of entry to NMI context
|
||||
* @irq: Is this call from rcu_irq_enter?
|
||||
*
|
||||
* If the CPU was idle from RCU's viewpoint, update rdtp->dynticks and
|
||||
* rdtp->dynticks_nmi_nesting to let the RCU grace-period handling know
|
||||
|
@ -929,10 +941,10 @@ void rcu_user_exit(void)
|
|||
* long as the nesting level does not overflow an int. (You will probably
|
||||
* run out of stack space first.)
|
||||
*
|
||||
* If you add or remove a call to rcu_nmi_enter(), be sure to test
|
||||
* If you add or remove a call to rcu_nmi_enter_common(), be sure to test
|
||||
* with CONFIG_RCU_EQS_DEBUG=y.
|
||||
*/
|
||||
void rcu_nmi_enter(void)
|
||||
static __always_inline void rcu_nmi_enter_common(bool irq)
|
||||
{
|
||||
struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
|
||||
long incby = 2;
|
||||
|
@ -949,7 +961,15 @@ void rcu_nmi_enter(void)
|
|||
* period (observation due to Andy Lutomirski).
|
||||
*/
|
||||
if (rcu_dynticks_curr_cpu_in_eqs()) {
|
||||
|
||||
if (irq)
|
||||
rcu_dynticks_task_exit();
|
||||
|
||||
rcu_dynticks_eqs_exit();
|
||||
|
||||
if (irq)
|
||||
rcu_cleanup_after_idle();
|
||||
|
||||
incby = 1;
|
||||
}
|
||||
trace_rcu_dyntick(incby == 1 ? TPS("Endirq") : TPS("++="),
|
||||
|
@ -960,6 +980,14 @@ void rcu_nmi_enter(void)
|
|||
barrier();
|
||||
}
|
||||
|
||||
/**
|
||||
* rcu_nmi_enter - inform RCU of entry to NMI context
|
||||
*/
|
||||
void rcu_nmi_enter(void)
|
||||
{
|
||||
rcu_nmi_enter_common(false);
|
||||
}
|
||||
|
||||
/**
|
||||
* rcu_irq_enter - inform RCU that current CPU is entering irq away from idle
|
||||
*
|
||||
|
@ -984,14 +1012,8 @@ void rcu_nmi_enter(void)
|
|||
*/
|
||||
void rcu_irq_enter(void)
|
||||
{
|
||||
struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
|
||||
|
||||
lockdep_assert_irqs_disabled();
|
||||
if (rdtp->dynticks_nmi_nesting == 0)
|
||||
rcu_dynticks_task_exit();
|
||||
rcu_nmi_enter();
|
||||
if (rdtp->dynticks_nmi_nesting == 1)
|
||||
rcu_cleanup_after_idle();
|
||||
rcu_nmi_enter_common(true);
|
||||
}
|
||||
|
||||
/*
|
||||
|
|
Loading…
Reference in New Issue
Block a user