For allocating new exch from pool, scanning for free slot in exch
array fluctuates when exch pool is close to exhaustion.
The fluctuation is smoothed, and the scan looks to be O(2).
Signed-off-by: Hillf Danton <dhillf@xxxxxxxxx>
---
--- a/drivers/scsi/libfc/fc_exch.c 2010-09-13 07:07:38.000000000 +0800
+++ b/drivers/scsi/libfc/fc_exch.c 2010-10-22 20:02:54.000000000 +0800
@@ -67,6 +67,11 @@ struct workqueue_struct *fc_exch_workque
struct fc_exch_pool {
u16 next_index;
u16 total_exches;
+
+ /* two cache of free slot in exch array */
+ u16 left;
+ u16 right;
+
spinlock_t lock;
struct list_head ex_list;
};
@@ -397,13 +402,26 @@ static inline void fc_exch_ptr_set(struc
static void fc_exch_delete(struct fc_exch *ep)
{
struct fc_exch_pool *pool;
+ u16 index;
pool = ep->pool;
spin_lock_bh(&pool->lock);
WARN_ON(pool->total_exches <= 0);
pool->total_exches--;
- fc_exch_ptr_set(pool, (ep->xid - ep->em->min_xid) >> fc_cpu_order,
- NULL);
+
+ /* update cache of free slot */
+ index = (ep->xid - ep->em->min_xid) >> fc_cpu_order;
+ if (pool->left == FC_XID_UNKNOWN)
+ pool->left = index;
+ else if (pool->right == FC_XID_UNKNOWN)
+ pool->right = index;
+ else
+ /* XXX
+ * next = entropy(index, left, right);
+ **/
+ pool->next_index = index;
+
+ fc_exch_ptr_set(pool, index, NULL);
list_del(&ep->ex_list);
spin_unlock_bh(&pool->lock);
fc_exch_release(ep); /* drop hold for exch in mp */
@@ -679,6 +697,19 @@ static struct fc_exch *fc_exch_em_alloc(
pool = per_cpu_ptr(mp->pool, cpu);
spin_lock_bh(&pool->lock);
put_cpu();
+
+ /* peek cache of free slot */
+ if (pool->left != FC_XID_UNKNOWN) {
+ index = pool->left;
+ pool->left = FC_XID_UNKNOWN;
+ goto hit;
+ }
+ if (pool->right != FC_XID_UNKNOWN) {
+ index = pool->right;
+ pool->right = FC_XID_UNKNOWN;
+ goto hit;
+ }
+
index = pool->next_index;
/* allocate new exch from pool */
while (fc_exch_ptr_get(pool, index)) {
@@ -687,7 +718,7 @@ static struct fc_exch *fc_exch_em_alloc(
goto err;
}
pool->next_index = index == mp->pool_max_index ? 0 : index + 1;
-
+hit:
fc_exch_hold(ep); /* hold for exch in mp */
spin_lock_init(&ep->ex_lock);
/*
@@ -2181,6 +2212,8 @@ struct fc_exch_mgr *fc_exch_mgr_alloc(st
goto free_mempool;
for_each_possible_cpu(cpu) {
pool = per_cpu_ptr(mp->pool, cpu);
+ pool->left =
+ pool->right = FC_XID_UNKNOWN;
spin_lock_init(&pool->lock);
INIT_LIST_HEAD(&pool->ex_list);
}
--
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