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rcu: optimize rcutiny

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rcu_sched_qs() currently calls local_irq_save()/local_irq_restore() up
to three times.

Remove irq masking from rcu_qsctr_help() / invoke_rcu_kthread()
and do it once in rcu_sched_qs() / rcu_bh_qs()

This generates smaller code as well.

   text	   data	    bss	    dec	    hex	filename
   2314	    156	     24	   2494	    9be	kernel/rcutiny.old.o
   2250	    156	     24	   2430	    97e	kernel/rcutiny.new.o

Fix an outdated comment for rcu_qsctr_help()
Move invoke_rcu_kthread() definition before its use.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
This commit is contained in:
Eric Dumazet 2011-04-28 07:23:45 +02:00 committed by Paul E. McKenney
parent 2655d57ef3
commit b554d7de8d
1 changed files with 21 additions and 22 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

43
kernel/rcutiny.c
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@ -40,10 +40,10 @@
static struct task_struct *rcu_kthread_task;
static DECLARE_WAIT_QUEUE_HEAD(rcu_kthread_wq);
static unsigned long have_rcu_kthread_work;
static void invoke_rcu_kthread(void);
/* Forward declarations for rcutiny_plugin.h. */
struct rcu_ctrlblk;
static void invoke_rcu_kthread(void);
static void rcu_process_callbacks(struct rcu_ctrlblk *rcp);
static int rcu_kthread(void *arg);
static void __call_rcu(struct rcu_head *head,
@ -79,26 +79,31 @@ void rcu_exit_nohz(void)
#endif /* #ifdef CONFIG_NO_HZ */
/*
* Helper function for rcu_qsctr_inc() and rcu_bh_qsctr_inc().
* Also disable irqs to avoid confusion due to interrupt handlers
* Helper function for rcu_sched_qs() and rcu_bh_qs().
* Also irqs are disabled to avoid confusion due to interrupt handlers
* invoking call_rcu().
*/
static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
{
unsigned long flags;
local_irq_save(flags);
if (rcp->rcucblist != NULL &&
rcp->donetail != rcp->curtail) {
rcp->donetail = rcp->curtail;
local_irq_restore(flags);
return 1;
}
local_irq_restore(flags);
return 0;
}
/*
* Wake up rcu_kthread() to process callbacks now eligible for invocation
* or to boost readers.
*/
static void invoke_rcu_kthread(void)
{
have_rcu_kthread_work = 1;
wake_up(&rcu_kthread_wq);
}
/*
* Record an rcu quiescent state. And an rcu_bh quiescent state while we
* are at it, given that any rcu quiescent state is also an rcu_bh
@ -106,9 +111,13 @@ static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
*/
void rcu_sched_qs(int cpu)
{
unsigned long flags;
local_irq_save(flags);
if (rcu_qsctr_help(&rcu_sched_ctrlblk) +
rcu_qsctr_help(&rcu_bh_ctrlblk))
invoke_rcu_kthread();
local_irq_restore(flags);
}
/*
@ -116,8 +125,12 @@ void rcu_sched_qs(int cpu)
*/
void rcu_bh_qs(int cpu)
{
unsigned long flags;
local_irq_save(flags);
if (rcu_qsctr_help(&rcu_bh_ctrlblk))
invoke_rcu_kthread();
local_irq_restore(flags);
}
/*
@ -207,20 +220,6 @@ static int rcu_kthread(void *arg)
return 0; /* Not reached, but needed to shut gcc up. */
}
/*
* Wake up rcu_kthread() to process callbacks now eligible for invocation
* or to boost readers.
*/
static void invoke_rcu_kthread(void)
{
unsigned long flags;
local_irq_save(flags);
have_rcu_kthread_work = 1;
wake_up(&rcu_kthread_wq);
local_irq_restore(flags);
}
/*
* Wait for a grace period to elapse. But it is illegal to invoke
* synchronize_sched() from within an RCU read-side critical section.