Messages in this thread | | | Subject | Re: [PATCH 2/7] iommu/iova: cut down judgement times | From | "Leizhen (ThunderTown)" <> | Date | Fri, 31 Mar 2017 11:55:38 +0800 |
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On 2017/3/23 20:11, Robin Murphy wrote: > On 22/03/17 06:27, Zhen Lei wrote: >> Below judgement can only be satisfied at the last time, which produced 2N >> judgements(suppose N times failed, 0 or 1 time successed) in vain. >> >> if ((pfn >= iova->pfn_lo) && (pfn <= iova->pfn_hi)) { >> return iova; >> } > > For me, GCC (6.2.1 AArch64) seems to do a pretty good job of this > function already, so this change only saves two instructions in total > (pfn is compared against pfn_lo only once instead of twice), which I > wouldn't expect to see a noticeable performance effect from. OK, thanks for your careful analysis.
Although only two instructions saved in each loop iteration, but it's also an improvment and no harm.
> > Given the improvement in readability, though, I don't even care about > any codegen differences :) > > Reviewed-by: Robin Murphy <robin.murphy@arm.com> > >> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.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 8ba8b496..1c49969 100644 >> --- a/drivers/iommu/iova.c >> +++ b/drivers/iommu/iova.c >> @@ -312,15 +312,12 @@ 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; >> > > > . >
-- Thanks! BestRegards
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