From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753034AbcEYKRz (ORCPT ); Wed, 25 May 2016 06:17:55 -0400 Received: from foss.arm.com ([217.140.101.70]:33727 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752957AbcEYKRx (ORCPT ); Wed, 25 May 2016 06:17:53 -0400 Subject: Re: [PATCH] iommu/vt-d: reduce extra first level entry in iommu->domains To: Wei Yang References: <1463798511-4015-1-git-send-email-richard.weiyang@gmail.com> <20160524230655.GA28550@vultr.guest> Cc: dwmw2@infradead.org, iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org From: Robin Murphy Message-ID: <57457BCD.7080909@arm.com> Date: Wed, 25 May 2016 11:17:49 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.8.0 MIME-Version: 1.0 In-Reply-To: <20160524230655.GA28550@vultr.guest> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. 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 >> --- >> 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 >