linux-kernel - Re: [PATCH] iommu/vt-d: reduce extra first level entry in iommu->domains

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Date:	Tue, 24 May 2016 23:06:55 +0000
From:	Wei Yang <richard.weiyang@...il.com>
To:	Wei Yang <richard.weiyang@...il.com>
Cc:	joro@...tes.org, dwmw2@...radead.org,
	iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iommu/vt-d: reduce extra first level entry in
 iommu->domains

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 :-)

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.weiyang@...il.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