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SubjectRe: [PATCH] iommu: Improve the performance for direct_mapping
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On Mon, 2020-11-23 at 12:32 +0000, Will Deacon wrote:
> On Fri, Nov 20, 2020 at 05:06:28PM +0800, Yong Wu wrote:
> > Currently direct_mapping always use the smallest pgsize which is SZ_4K
> > normally to mapping. This is unnecessary. we could gather the size, and
> > call iommu_map then, iommu_map could decide how to map better with the
> > just right pgsize.
> >
> > From the original comment, we should take care overlap, otherwise,
> > iommu_map may return -EEXIST. In this overlap case, we should map the
> > previous region before overlap firstly. then map the left part.
> >
> > Each a iommu device will call this direct_mapping when its iommu
> > initialize, This patch is effective to improve the boot/initialization
> > time especially while it only needs level 1 mapping.
> >
> > Signed-off-by: Anan Sun <anan.sun@mediatek.com>
> > Signed-off-by: Yong Wu <yong.wu@mediatek.com>
> > ---
> > drivers/iommu/iommu.c | 20 ++++++++++++++++++--
> > 1 file changed, 18 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> > index df87c8e825f7..854a8fcb928d 100644
> > --- a/drivers/iommu/iommu.c
> > +++ b/drivers/iommu/iommu.c
> > @@ -737,6 +737,7 @@ static int iommu_create_device_direct_mappings(struct iommu_group *group,
> > /* We need to consider overlapping regions for different devices */
> > list_for_each_entry(entry, &mappings, list) {
> > dma_addr_t start, end, addr;
> > + size_t unmapped_sz = 0;
>
> I think "unmapped" is the wrong word here, as this variable actually
> represents the amount we want to map! I suggest "map_size" instead.
>
> > if (domain->ops->apply_resv_region)
> > domain->ops->apply_resv_region(dev, domain, entry);
> > @@ -752,10 +753,25 @@ static int iommu_create_device_direct_mappings(struct iommu_group *group,
> > phys_addr_t phys_addr;
> >
> > phys_addr = iommu_iova_to_phys(domain, addr);
> > - if (phys_addr)
> > + if (phys_addr == 0) {
> > + unmapped_sz += pg_size; /* Gather the size. */
> > continue;
> > + }
> >
> > - ret = iommu_map(domain, addr, addr, pg_size, entry->prot);
> > + if (unmapped_sz) {
> > + /* Map the region before the overlap. */
> > + ret = iommu_map(domain, start, start,
> > + unmapped_sz, entry->prot);
> > + if (ret)
> > + goto out;
> > + start += unmapped_sz;
>
> I think it's a bit confusing to update start like this. Can we call
> iommu_map(domain, addr - map_size, addr - map_size, map_size, entry->prot)
> instead?
>
> > + unmapped_sz = 0;
> > + }
> > + start += pg_size;
> > + }
> > + if (unmapped_sz) {
> > + ret = iommu_map(domain, start, start, unmapped_sz,
> > + entry->prot);
>
> Can you avoid this hunk by changing your loop check to something like:
>
> if (!phys_addr) {
> map_size += pg_size;
> if (addr + pg_size < end)
> continue;
> }

Thanks for your quick review. I have fixed and tested it. the patch is
simple. I copy it here. Is this readable for you now?


--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -737,6 +737,7 @@ static int
iommu_create_device_direct_mappings(struct iommu_group *group,
/* We need to consider overlapping regions for different devices */
list_for_each_entry(entry, &mappings, list) {
dma_addr_t start, end, addr;
+ size_t map_size = 0;

if (domain->ops->apply_resv_region)
domain->ops->apply_resv_region(dev, domain, entry);
@@ -752,12 +753,21 @@ static int
iommu_create_device_direct_mappings(struct iommu_group *group,
phys_addr_t phys_addr;

phys_addr = iommu_iova_to_phys(domain, addr);
- if (phys_addr)
- continue;
+ if (!phys_addr) {
+ map_size += pg_size;
+ if (addr + pg_size < end)
+ continue;
+ else
+ addr += pg_size; /*Point to End */
+ }

- ret = iommu_map(domain, addr, addr, pg_size, entry->prot);
- if (ret)
- goto out;
+ if (map_size) {
+ ret = iommu_map(domain, addr - map_size, addr - map_size,
+ map_size, entry->prot);
+ if (ret)
+ goto out;
+ map_size = 0;
+ }
}

>
> Will

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