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iommu/iova: Optimise rbtree searching 

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>
Tested-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Tested-by: Zhen Lei <thunder.leizhen@huawei.com>
Tested-by: Nate Watterson <nwatters@codeaurora.org>
[rm: rewrote commit message to clarify]
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>
This commit is contained in:
Zhen Lei 2017-09-21 16:52:42 +01:00 committed by Joerg Roedel
parent e19b205be4
commit 2070f940a6
1 changed files with 3 additions and 6 deletions
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9
drivers/iommu/iova.c
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@ -342,15 +342,12 @@ 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;