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Commit b554d7de authored by Eric Dumazet's avatar Eric Dumazet Committed by Paul E. McKenney
Browse files

rcu: optimize rcutiny 



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Fix an outdated comment for rcu_qsctr_help()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: default avatarEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: default avatarJosh Triplett <josh@joshtriplett.org>
parent 2655d57e

kernel/rcutiny.c

+21 −22
Original line number Diff line number Diff line
@@ -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.