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Groups > linux.kernel > #1690464

[PATCH 1/4] iommu/iova: Optimise rbtree searching

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From: Zhen Lei <thunder.leizhen@huawei.com>

Checking the IOVA bounds separately before deciding which direction to
continue the search (if necessary) results in redundantly comparing both
pfns twice each. GCC can already determine that the final comparison op
is redundant and optimise it down to 3 in total, but we can go one
further with a little tweak of the ordering (which makes the intent of
the code that much cleaner as a bonus).

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
[rm: rewrote commit message to clarify]
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---
 drivers/iommu/iova.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c
index 246f14c83944..8f7552dc4e04 100644
--- a/drivers/iommu/iova.c
+++ b/drivers/iommu/iova.c
@@ -289,15 +289,12 @@ private_find_iova(struct iova_domain *iovad, unsigned long pfn)
 	while (node) {
 		struct iova *iova = rb_entry(node, struct iova, node);
 
-		/* If pfn falls within iova's range, return iova */
-		if ((pfn >= iova->pfn_lo) && (pfn <= iova->pfn_hi)) {
-			return iova;
-		}
-
 		if (pfn < iova->pfn_lo)
 			node = node->rb_left;
-		else if (pfn > iova->pfn_lo)
+		else if (pfn > iova->pfn_hi)
 			node = node->rb_right;
+		else
+			return iova;	/* pfn falls within iova's range */
 	}
 
 	return NULL;
-- 
2.12.2.dirty

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[PATCH 0/4] Optimise 64-bit IOVA allocations Robin Murphy <robin.murphy@arm.com> - 2017-07-18 19:10 +0200
  [PATCH 1/4] iommu/iova: Optimise rbtree searching Robin Murphy <robin.murphy@arm.com> - 2017-07-18 19:10 +0200
  [PATCH 3/4] iommu/iova: Extend rbtree node caching Robin Murphy <robin.murphy@arm.com> - 2017-07-18 19:10 +0200
  [PATCH 2/4] iommu/iova: Optimise the padding calculation Robin Murphy <robin.murphy@arm.com> - 2017-07-18 19:10 +0200
  [PATCH 4/4] iommu/iova: Make dma_32bit_pfn implicit Robin Murphy <robin.murphy@arm.com> - 2017-07-18 19:10 +0200
  Re: [PATCH 0/4] Optimise 64-bit IOVA allocations Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2017-07-19 10:40 +0200
    Re: [PATCH 0/4] Optimise 64-bit IOVA allocations Robin Murphy <robin.murphy@arm.com> - 2017-07-19 12:30 +0200
      Re: [PATCH 0/4] Optimise 64-bit IOVA allocations "Leizhen (ThunderTown)" <thunder.leizhen@huawei.com> - 2017-07-21 11:50 +0200

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