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rcu: Don't redundantly disable irqs in rcu_irq_{enter,exit}()

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This commit replaces a local_irq_save()/local_irq_restore() pair with
a lockdep assertion that interrupts are already disabled.  This should
remove the corresponding overhead from the interrupt entry/exit fastpaths.

This change was inspired by the fact that Iftekhar Ahmed's mutation
testing showed that removing rcu_irq_enter()'s call to local_ird_restore()
had no effect, which might indicate that interrupts were always enabled
anyway.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney
2015-10-31 00:59:01 -07:00
parent d117c8aa1d
commit 7c9906ca5e
5 changed files with 40 additions and 10 deletions
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32
kernel/rcu/tree.c
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@@ -732,7 +732,7 @@ void rcu_user_enter(void)
*
* Exit from an interrupt handler, which might possibly result in entering
* idle mode, in other words, leaving the mode in which read-side critical
* sections can occur.
* sections can occur. The caller must have disabled interrupts.
*
* This code assumes that the idle loop never does anything that might
* result in unbalanced calls to irq_enter() and irq_exit(). If your
@@ -745,11 +745,10 @@ void rcu_user_enter(void)
*/
void rcu_irq_exit(void)
{
unsigned long flags;
long long oldval;
struct rcu_dynticks *rdtp;
local_irq_save(flags);
RCU_LOCKDEP_WARN(!irqs_disabled(), "rcu_irq_exit() invoked with irqs enabled!!!");
rdtp = this_cpu_ptr(&rcu_dynticks);
oldval = rdtp->dynticks_nesting;
rdtp->dynticks_nesting--;
@@ -760,6 +759,17 @@ void rcu_irq_exit(void)
else
rcu_eqs_enter_common(oldval, true);
rcu_sysidle_enter(1);
}
/*
* Wrapper for rcu_irq_exit() where interrupts are enabled.
*/
void rcu_irq_exit_irqson(void)
{
unsigned long flags;
local_irq_save(flags);
rcu_irq_exit();
local_irq_restore(flags);
}
@@ -857,7 +867,7 @@ void rcu_user_exit(void)
*
* Enter an interrupt handler, which might possibly result in exiting
* idle mode, in other words, entering the mode in which read-side critical
* sections can occur.
* sections can occur. The caller must have disabled interrupts.
*
* Note that the Linux kernel is fully capable of entering an interrupt
* handler that it never exits, for example when doing upcalls to
@@ -873,11 +883,10 @@ void rcu_user_exit(void)
*/
void rcu_irq_enter(void)
{
unsigned long flags;
struct rcu_dynticks *rdtp;
long long oldval;
local_irq_save(flags);
RCU_LOCKDEP_WARN(!irqs_disabled(), "rcu_irq_enter() invoked with irqs enabled!!!");
rdtp = this_cpu_ptr(&rcu_dynticks);
oldval = rdtp->dynticks_nesting;
rdtp->dynticks_nesting++;
@@ -888,6 +897,17 @@ void rcu_irq_enter(void)
else
rcu_eqs_exit_common(oldval, true);
rcu_sysidle_exit(1);
}
/*
* Wrapper for rcu_irq_enter() where interrupts are enabled.
*/
void rcu_irq_enter_irqson(void)
{
unsigned long flags;
local_irq_save(flags);
rcu_irq_enter();
local_irq_restore(flags);
}