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 <[email protected]>
>
>> Signed-off-by: Zhen Lei <[email protected]>
>> ---
>> 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
