On Wed, May 25, 2016 at 11:17:49AM +0100, Robin Murphy wrote: >On 25/05/16 00:06, Wei Yang wrote: >>Hi, Joerg >> >>Not sure whether you think this calculation is correct. >> >>If I missed something for this " + 1" in your formula, I am glad to hear your >>explanation. So that I could learn something from you :-) > >I'm not familiar enough with this aspect of the driver to confirm whether the >change is appropriate or not, but it does seem worth noting that using >DIV_ROUND_UP would be an even neater approach. >
Hi, Robin, Thanks for your comment. Yes, I agree DIV_ROUND_UP would make the code more easy to read. I have thought about using DIV_ROUND_UP, while from the definition DIV_ROUND_UP use operation "/", and ALIGN use bit operation. So the change in my patch chooses the second one and tries to keep the efficiency. >Robin. > >>Have a good day~ >> >>On Sat, May 21, 2016 at 02:41:51AM +0000, Wei Yang wrote: >>>In commit <8bf478163e69> ("iommu/vt-d: Split up iommu->domains array"), it >>>it splits iommu->domains in two levels. Each first level contains 256 >>>entries of second level. In case of the ndomains is exact a multiple of >>>256, it would have one more extra first level entry for current >>>implementation. >>> >>>This patch refines this calculation to reduce the extra first level entry. >>> >>>Signed-off-by: Wei Yang <richard.weiy...@gmail.com> >>>--- >>>drivers/iommu/intel-iommu.c | 4 ++-- >>>1 file changed, 2 insertions(+), 2 deletions(-) >>> >>>diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c >>>index e3061d3..2204ca4 100644 >>>--- a/drivers/iommu/intel-iommu.c >>>+++ b/drivers/iommu/intel-iommu.c >>>@@ -1634,7 +1634,7 @@ static int iommu_init_domains(struct intel_iommu >>>*iommu) >>> return -ENOMEM; >>> } >>> >>>- size = ((ndomains >> 8) + 1) * sizeof(struct dmar_domain **); >>>+ size = (ALIGN(ndomains, 256) >> 8) * sizeof(struct dmar_domain **); >>> iommu->domains = kzalloc(size, GFP_KERNEL); >>> >>> if (iommu->domains) { >>>@@ -1699,7 +1699,7 @@ static void disable_dmar_iommu(struct intel_iommu >>>*iommu) >>>static void free_dmar_iommu(struct intel_iommu *iommu) >>>{ >>> if ((iommu->domains) && (iommu->domain_ids)) { >>>- int elems = (cap_ndoms(iommu->cap) >> 8) + 1; >>>+ int elems = ALIGN(cap_ndoms(iommu->cap), 256) >> 8; >>> int i; >>> >>> for (i = 0; i < elems; i++) >>>-- >>>1.7.9.5 >> -- Wei Yang Help you, Help me