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

Conflicts:

	kernel/srcu.c
This commit is contained in:
Lai Jiangshan 2012-03-19 16:12:12 +08:00 committed by Paul E. McKenney
parent dc87917501
commit d9792edd7a
1 changed files with 14 additions and 13 deletions
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27
kernel/srcu.c
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@ -266,16 +266,16 @@ EXPORT_SYMBOL_GPL(__srcu_read_unlock);
* we repeatedly block for 1-millisecond time periods. This approach * we repeatedly block for 1-millisecond time periods. This approach
* has done well in testing, so there is no need for a config parameter. * has done well in testing, so there is no need for a config parameter.
*/ */
#define SYNCHRONIZE_SRCU_READER_DELAY 5 #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 * Wait until all pre-existing readers complete. Such readers
* will have used the index specified by "idx". * 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 * SRCU read-side critical sections are normally short, so wait
* a small amount of time before possibly blocking. * 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)) { if (!srcu_readers_active_idx_check(sp, idx)) {
udelay(SYNCHRONIZE_SRCU_READER_DELAY); udelay(SYNCHRONIZE_SRCU_READER_DELAY);
while (!srcu_readers_active_idx_check(sp, idx)) { while (!srcu_readers_active_idx_check(sp, idx)) {
if (expedited && ++ trycount < 10) if (trycount > 0) {
trycount--;
udelay(SYNCHRONIZE_SRCU_READER_DELAY); udelay(SYNCHRONIZE_SRCU_READER_DELAY);
else } else
schedule_timeout_interruptible(1); 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(). * 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; int busy_idx;
@ -319,8 +320,8 @@ static void __synchronize_srcu(struct srcu_struct *sp, bool expedited)
* have completed: * have completed:
* *
* __synchronize_srcu() { * __synchronize_srcu() {
* wait_idx(sp, 0, expedited); * wait_idx(sp, 0, trycount);
* wait_idx(sp, 1, expedited); * wait_idx(sp, 1, trycount);
* } * }
* *
* Starvation is prevented by the fact that we flip the index. * 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 * this call to wait_idx(), which waits on really old readers
* describe in this comment above, will almost never need to wait. * 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. */ /* Flip the index to avoid reader-induced starvation. */
srcu_flip(sp); srcu_flip(sp);
/* Wait for recent pre-existing readers. */ /* Wait for recent pre-existing readers. */
wait_idx(sp, busy_idx, expedited); wait_idx(sp, busy_idx, trycount);
mutex_unlock(&sp->mutex); 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) void synchronize_srcu(struct srcu_struct *sp)
{ {
__synchronize_srcu(sp, 0); __synchronize_srcu(sp, SYNCHRONIZE_SRCU_TRYCOUNT);
} }
EXPORT_SYMBOL_GPL(synchronize_srcu); EXPORT_SYMBOL_GPL(synchronize_srcu);
@ -392,7 +393,7 @@ EXPORT_SYMBOL_GPL(synchronize_srcu);
*/ */
void synchronize_srcu_expedited(struct srcu_struct *sp) 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); EXPORT_SYMBOL_GPL(synchronize_srcu_expedited);