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Date: Tue, 23 Aug 2022 15:00:55 -0700
From: Rob Clark <robdclark@...il.com>
To: Akhil P Oommen <quic_akhilpo@...cinc.com>
Cc: dri-devel@...ts.freedesktop.org,
Rob Clark <robdclark@...omium.org>,
Sai Prakash Ranjan <quic_saipraka@...cinc.com>,
David Airlie <airlied@...ux.ie>, linux-arm-msm@...r.kernel.org,
Abhinav Kumar <quic_abhinavk@...cinc.com>,
open list <linux-kernel@...r.kernel.org>,
Sean Paul <sean@...rly.run>, Daniel Vetter <daniel@...ll.ch>,
Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
freedreno@...ts.freedesktop.org
Subject: Re: [Freedreno] [PATCH v2] drm/msm/iommu: optimize map/unmap
On Tue, Aug 23, 2022 at 2:37 PM Akhil P Oommen <quic_akhilpo@...cinc.com> wrote:
>
> On 8/23/2022 10:07 PM, Rob Clark wrote:
> > From: Rob Clark <robdclark@...omium.org>
> >
> > Using map_pages/unmap_pages cuts down on the # of pgtable walks needed
> > in the process of finding where to insert/remove an entry. The end
> > result is ~5-10x faster than mapping a single page at a time.
> >
> > v2: Rename iommu_pgsize(), drop obsolete comments, fix error handling
> > in msm_iommu_pagetable_map()
> >
> > Signed-off-by: Rob Clark <robdclark@...omium.org>
> > ---
> > drivers/gpu/drm/msm/msm_iommu.c | 101 +++++++++++++++++++++++++++-----
> > 1 file changed, 86 insertions(+), 15 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/msm/msm_iommu.c b/drivers/gpu/drm/msm/msm_iommu.c
> > index a54ed354578b..5577cea7c009 100644
> > --- a/drivers/gpu/drm/msm/msm_iommu.c
> > +++ b/drivers/gpu/drm/msm/msm_iommu.c
> > @@ -21,6 +21,7 @@ struct msm_iommu_pagetable {
> > struct msm_mmu base;
> > struct msm_mmu *parent;
> > struct io_pgtable_ops *pgtbl_ops;
> > + unsigned long pgsize_bitmap; /* Bitmap of page sizes in use */
> > phys_addr_t ttbr;
> > u32 asid;
> > };
> > @@ -29,23 +30,84 @@ static struct msm_iommu_pagetable *to_pagetable(struct msm_mmu *mmu)
> > return container_of(mmu, struct msm_iommu_pagetable, base);
> > }
> >
> > +/* based on iommu_pgsize() in iommu.c: */
> > +static size_t calc_pgsize(struct msm_iommu_pagetable *pagetable,
> > + unsigned long iova, phys_addr_t paddr,
> > + size_t size, size_t *count)
> > +{
> > + unsigned int pgsize_idx, pgsize_idx_next;
> > + unsigned long pgsizes;
> > + size_t offset, pgsize, pgsize_next;
> > + unsigned long addr_merge = paddr | iova;
> > +
> > + /* Page sizes supported by the hardware and small enough for @size */
> > + pgsizes = pagetable->pgsize_bitmap & GENMASK(__fls(size), 0);
> > +
> > + /* Constrain the page sizes further based on the maximum alignment */
> > + if (likely(addr_merge))
> > + pgsizes &= GENMASK(__ffs(addr_merge), 0);
> > +
> > + /* Make sure we have at least one suitable page size */
> > + BUG_ON(!pgsizes);
> > +
> > + /* Pick the biggest page size remaining */
> > + pgsize_idx = __fls(pgsizes);
> > + pgsize = BIT(pgsize_idx);
> > + if (!count)
> > + return pgsize;
> > +
> > + /* Find the next biggest support page size, if it exists */
> > + pgsizes = pagetable->pgsize_bitmap & ~GENMASK(pgsize_idx, 0);
> > + if (!pgsizes)
> > + goto out_set_count;
> > +
> > + pgsize_idx_next = __ffs(pgsizes);
> > + pgsize_next = BIT(pgsize_idx_next);
> > +
> > + /*
> > + * There's no point trying a bigger page size unless the virtual
> > + * and physical addresses are similarly offset within the larger page.
> > + */
> > + if ((iova ^ paddr) & (pgsize_next - 1))
> > + goto out_set_count;
> > +
> > + /* Calculate the offset to the next page size alignment boundary */
> > + offset = pgsize_next - (addr_merge & (pgsize_next - 1));
> > +
> > + /*
> > + * If size is big enough to accommodate the larger page, reduce
> > + * the number of smaller pages.
> > + */
> > + if (offset + pgsize_next <= size)
> > + size = offset;
> > +
> > +out_set_count:
> > + *count = size >> pgsize_idx;
> > + return pgsize;
> > +}
> > +
> Can we keep this in iommu driver? Seems useful to other drivers too.
This might end up being only temporary.. Robin had the idea of adding
a private way to create "dummy" iommu_domain's which we could use
instead of the pgtbl ops directly. On one hand, it would simplify
this quite a bit. On the other hand it would force powering up (at
least the SMMU) for unmaps/maps, and make it harder to do things like
this:
https://patchwork.freedesktop.org/patch/498660/?series=107536&rev=1
> Perhaps implement an sg friendly version of iopgtble ops, like
> unmap_sg() maybe!
Probably not a good idea to push more into the iopgtbl
implementations.. __iommu_map_sg() does have a bit of cleverness, but
that shouldn't really be required if we get our sg from
drm_prime_pages_to_sg() since sg_alloc_append_table_from_pages()
already performs a similar merging
BR,
-R
>
> -Akhil.
> > static int msm_iommu_pagetable_unmap(struct msm_mmu *mmu, u64 iova,
> > size_t size)
> > {
> > struct msm_iommu_pagetable *pagetable = to_pagetable(mmu);
> > struct io_pgtable_ops *ops = pagetable->pgtbl_ops;
> > - size_t unmapped = 0;
> >
> > - /* Unmap the block one page at a time */
> > while (size) {
> > - unmapped += ops->unmap(ops, iova, 4096, NULL);
> > - iova += 4096;
> > - size -= 4096;
> > + size_t unmapped, pgsize, count;
> > +
> > + pgsize = calc_pgsize(pagetable, iova, iova, size, &count);
> > +
> > + unmapped = ops->unmap_pages(ops, iova, pgsize, count, NULL);
> > + if (!unmapped)
> > + break;
> > +
> > + iova += unmapped;
> > + size -= unmapped;
> > }
> >
> > iommu_flush_iotlb_all(to_msm_iommu(pagetable->parent)->domain);
> >
> > - return (unmapped == size) ? 0 : -EINVAL;
> > + return (size == 0) ? 0 : -EINVAL;
> > }
> >
> > static int msm_iommu_pagetable_map(struct msm_mmu *mmu, u64 iova,
> > @@ -54,7 +116,6 @@ static int msm_iommu_pagetable_map(struct msm_mmu *mmu, u64 iova,
> > struct msm_iommu_pagetable *pagetable = to_pagetable(mmu);
> > struct io_pgtable_ops *ops = pagetable->pgtbl_ops;
> > struct scatterlist *sg;
> > - size_t mapped = 0;
> > u64 addr = iova;
> > unsigned int i;
> >
> > @@ -62,17 +123,26 @@ static int msm_iommu_pagetable_map(struct msm_mmu *mmu, u64 iova,
> > size_t size = sg->length;
> > phys_addr_t phys = sg_phys(sg);
> >
> > - /* Map the block one page at a time */
> > while (size) {
> > - if (ops->map(ops, addr, phys, 4096, prot, GFP_KERNEL)) {
> > - msm_iommu_pagetable_unmap(mmu, iova, mapped);
> > + size_t pgsize, count, mapped = 0;
> > + int ret;
> > +
> > + pgsize = calc_pgsize(pagetable, addr, phys, size, &count);
> > +
> > + ret = ops->map_pages(ops, addr, phys, pgsize, count,
> > + prot, GFP_KERNEL, &mapped);
> > +
> > + /* map_pages could fail after mapping some of the pages,
> > + * so update the counters before error handling.
> > + */
> > + phys += mapped;
> > + addr += mapped;
> > + size -= mapped;
> > +
> > + if (ret) {
> > + msm_iommu_pagetable_unmap(mmu, iova, addr - iova);
> > return -EINVAL;
> > }
> > -
> > - phys += 4096;
> > - addr += 4096;
> > - size -= 4096;
> > - mapped += 4096;
> > }
> > }
> >
> > @@ -207,6 +277,7 @@ struct msm_mmu *msm_iommu_pagetable_create(struct msm_mmu *parent)
> >
> > /* Needed later for TLB flush */
> > pagetable->parent = parent;
> > + pagetable->pgsize_bitmap = ttbr0_cfg.pgsize_bitmap;
> > pagetable->ttbr = ttbr0_cfg.arm_lpae_s1_cfg.ttbr;
> >
> > /*
>
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