linux-kernel - [PATCH v2 6/7] iommu/iova: move the caculation of pad mask out of loop

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Message-ID: <1490930665-9696-7-git-send-email-thunder.leizhen@huawei.com>
Date:   Fri, 31 Mar 2017 11:24:24 +0800
From:   Zhen Lei <thunder.leizhen@...wei.com>
To:     Joerg Roedel <joro@...tes.org>,
        iommu <iommu@...ts.linux-foundation.org>,
        Robin Murphy <robin.murphy@....com>,
        David Woodhouse <dwmw2@...radead.org>,
        Sudeep Dutt <sudeep.dutt@...el.com>,
        Ashutosh Dixit <ashutosh.dixit@...el.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
CC:     Zefan Li <lizefan@...wei.com>, Xinwei Hu <huxinwei@...wei.com>,
        "Tianhong Ding" <dingtianhong@...wei.com>,
        Hanjun Guo <guohanjun@...wei.com>,
        Zhen Lei <thunder.leizhen@...wei.com>
Subject: [PATCH v2 6/7] iommu/iova: move the caculation of pad mask out of loop

I'm not sure whether the compiler can optimize it, but move it out will
be better. At least, it does not require lock protection.

Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
---
 drivers/iommu/iova.c | 22 ++++++++++------------
 1 file changed, 10 insertions(+), 12 deletions(-)

diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c
index 23abe84..68754e4 100644
--- a/drivers/iommu/iova.c
+++ b/drivers/iommu/iova.c
@@ -127,23 +127,16 @@ __cached_rbnode_delete_update(struct iova_domain *iovad, struct iova *free)
 		*cached_node = rb_prev(&free->node);
 }
 
-/*
- * Computes the padding size required, to make the start address
- * naturally aligned on the power-of-two order of its size
- */
-static unsigned long
-iova_get_pad_size(unsigned long size, unsigned long limit_pfn)
-{
-	return (limit_pfn + 1 - size) & (__roundup_pow_of_two(size) - 1);
-}
-
 static int __alloc_and_insert_iova_range(struct iova_domain *iovad,
 		unsigned long size, unsigned long limit_pfn,
 			struct iova *new, bool size_aligned)
 {
 	struct rb_node *prev, *curr;
 	unsigned long flags;
-	unsigned long pad_size = 0;
+	unsigned long pad_mask, pad_size = 0;
+
+	if (size_aligned)
+		pad_mask = __roundup_pow_of_two(size) - 1;
 
 	/* Walk the tree backwards */
 	spin_lock_irqsave(&iovad->iova_rbtree_lock, flags);
@@ -157,8 +150,13 @@ static int __alloc_and_insert_iova_range(struct iova_domain *iovad,
 		else if (limit_pfn < curr_iova->pfn_hi)
 			goto adjust_limit_pfn;
 		else {
+			/*
+			 * Computes the padding size required, to make the start
+			 * address naturally aligned on the power-of-two order
+			 * of its size
+			 */
 			if (size_aligned)
-				pad_size = iova_get_pad_size(size, limit_pfn);
+				pad_size = (limit_pfn + 1 - size) & pad_mask;
 			if ((curr_iova->pfn_hi + size + pad_size) <= limit_pfn)
 				break;	/* found a free slot */
 		}
-- 
2.5.0