From mboxrd@z Thu Jan 1 00:00:00 1970 From: Robert Love Subject: [PATCH 04/27] libfc: tune fc_exch_em_alloc() to be O(2) Date: Tue, 30 Nov 2010 16:18:17 -0800 Message-ID: <20101201001817.18369.74436.stgit@localhost.localdomain> References: <20101201001756.18369.7107.stgit@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Return-path: Received: from mga11.intel.com ([192.55.52.93]:26582 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752489Ab0LAASS (ORCPT ); Tue, 30 Nov 2010 19:18:18 -0500 In-Reply-To: <20101201001756.18369.7107.stgit@localhost.localdomain> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: James.Bottomley@suse.de, linux-scsi@vger.kernel.org Cc: Hillf Danton From: Hillf Danton 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 Signed-off-by: Robert Love --- drivers/scsi/libfc/fc_exch.c | 36 +++++++++++++++++++++++++++++++++--- 1 files changed, 33 insertions(+), 3 deletions(-) diff --git a/drivers/scsi/libfc/fc_exch.c b/drivers/scsi/libfc/fc_exch.c index d0df1b2..46973d6 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); }