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Commit d9792edd authored by Lai Jiangshan's avatar Lai Jiangshan Committed by Paul E. McKenney
Browse files

rcu: Use single value to handle expedited SRCU grace periods 



The earlier algorithm used an "expedited" flag combined with a "trycount"
counter to differentiate between normal and expedited SRCU grace periods.
However, the difference can be encoded into a single counter with a cutoff
value and different initial values for expedited and normal SRCU grace
periods.  This commit makes that change.

Signed-off-by: default avatarLai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>

Conflicts:

	kernel/srcu.c
parent dc879175

kernel/srcu.c

+14 −13
Original line number Diff line number Diff line
@@ -267,15 +267,15 @@ EXPORT_SYMBOL_GPL(__srcu_read_unlock); 
 * has done well in testing, so there is no need for a config parameter.

 */

#define SYNCHRONIZE_SRCU_READER_DELAY	5

#define SYNCHRONIZE_SRCU_TRYCOUNT	2

#define SYNCHRONIZE_SRCU_EXP_TRYCOUNT	12



/*

 * Wait until all pre-existing readers complete.  Such readers

 * will have used the index specified by "idx".

 */

static void wait_idx(struct srcu_struct *sp, int idx, bool expedited)

static void wait_idx(struct srcu_struct *sp, int idx, int trycount)

{

	int trycount = 0;



	/*

	 * SRCU read-side critical sections are normally short, so wait

	 * a small amount of time before possibly blocking.
@@ -283,9 +283,10 @@ static void wait_idx(struct srcu_struct *sp, int idx, bool expedited) 
	if (!srcu_readers_active_idx_check(sp, idx)) {

		udelay(SYNCHRONIZE_SRCU_READER_DELAY);

		while (!srcu_readers_active_idx_check(sp, idx)) {

			if (expedited && ++ trycount < 10)

			if (trycount > 0) {

				trycount--;

				udelay(SYNCHRONIZE_SRCU_READER_DELAY);

			else

			} else

				schedule_timeout_interruptible(1);

		}

	}
@@ -299,7 +300,7 @@ static void srcu_flip(struct srcu_struct *sp) 
/*

 * Helper function for synchronize_srcu() and synchronize_srcu_expedited().

 */

static void __synchronize_srcu(struct srcu_struct *sp, bool expedited)

static void __synchronize_srcu(struct srcu_struct *sp, int trycount)

{

	int busy_idx;
@@ -319,8 +320,8 @@ static void __synchronize_srcu(struct srcu_struct *sp, bool expedited) 
	 * have completed:

	 *

	 * __synchronize_srcu() {

	 * 	wait_idx(sp, 0, expedited);

	 * 	wait_idx(sp, 1, expedited);

	 * 	wait_idx(sp, 0, trycount);

	 * 	wait_idx(sp, 1, trycount);

	 * }

	 *

	 * Starvation is prevented by the fact that we flip the index.
@@ -344,13 +345,13 @@ static void __synchronize_srcu(struct srcu_struct *sp, bool expedited) 
	 * this call to wait_idx(), which waits on really old readers

	 * describe in this comment above, will almost never need to wait.

	 */

	wait_idx(sp, 1 - busy_idx, expedited);

	wait_idx(sp, 1 - busy_idx, trycount);



	/* Flip the index to avoid reader-induced starvation. */

	srcu_flip(sp);



	/* Wait for recent pre-existing readers. */

	wait_idx(sp, busy_idx, expedited);

	wait_idx(sp, busy_idx, trycount);



	mutex_unlock(&sp->mutex);

}
@@ -371,7 +372,7 @@ static void __synchronize_srcu(struct srcu_struct *sp, bool expedited) 
 */

void synchronize_srcu(struct srcu_struct *sp)

{

	__synchronize_srcu(sp, 0);

	__synchronize_srcu(sp, SYNCHRONIZE_SRCU_TRYCOUNT);

}

EXPORT_SYMBOL_GPL(synchronize_srcu);
@@ -392,7 +393,7 @@ EXPORT_SYMBOL_GPL(synchronize_srcu); 
 */

void synchronize_srcu_expedited(struct srcu_struct *sp)

{

	__synchronize_srcu(sp, 1);

	__synchronize_srcu(sp, SYNCHRONIZE_SRCU_EXP_TRYCOUNT);

}

EXPORT_SYMBOL_GPL(synchronize_srcu_expedited);