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authorHillf Danton <dhillf@gmail.com>2010-11-30 16:18:17 -0800
committerJames Bottomley <James.Bottomley@suse.de>2010-12-21 12:24:19 -0600
commit2034c19ce8f8503aa14cb1e763fbfe60316aaa8e (patch)
treea041e219fe6342d6268d71581d94c02073f681f6 /drivers/scsi/libfc
parent8236554a27af870ecd1cd588d9558ccdc212037b (diff)
[SCSI] libfc: tune fc_exch_em_alloc() to be O(2)
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@gmail.com> Signed-off-by: Robert Love <robert.w.love@intel.com> Signed-off-by: James Bottomley <James.Bottomley@suse.de>
Diffstat (limited to 'drivers/scsi/libfc')
-rw-r--r--drivers/scsi/libfc/fc_exch.c36
1 files changed, 33 insertions, 3 deletions
diff --git a/drivers/scsi/libfc/fc_exch.c b/drivers/scsi/libfc/fc_exch.c
index d0df1b2faf2..46973d6618d 100644
--- a/drivers/scsi/libfc/fc_exch.c
+++ b/drivers/scsi/libfc/fc_exch.c
@@ -67,6 +67,11 @@ struct workqueue_struct *fc_exch_workqueue;
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;
};
@@ -396,13 +401,23 @@ static inline void fc_exch_ptr_set(struct fc_exch_pool *pool, u16 index,
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
+ 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 */
@@ -678,6 +693,19 @@ static struct fc_exch *fc_exch_em_alloc(struct fc_lport *lport,
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)) {
@@ -686,7 +714,7 @@ static struct fc_exch *fc_exch_em_alloc(struct fc_lport *lport,
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);
/*
@@ -2180,6 +2208,8 @@ struct fc_exch_mgr *fc_exch_mgr_alloc(struct fc_lport *lport,
goto free_mempool;
for_each_possible_cpu(cpu) {
pool = per_cpu_ptr(mp->pool, cpu);
+ pool->left = FC_XID_UNKNOWN;
+ pool->right = FC_XID_UNKNOWN;
spin_lock_init(&pool->lock);
INIT_LIST_HEAD(&pool->ex_list);
}