On Thu, Feb 19, 2026 at 12:10:57PM -0800, Matthew Brost wrote: > The dma-map IOVA alloc, link, and sync APIs perform significantly better > than dma-map / dma-unmap, as they avoid costly IOMMU synchronizations. > This difference is especially noticeable when mapping a 2MB region in > 4KB pages.
Still a good improvement but with device THP now in drm-tip for GPU SVM, the speedup is less noticeable when looking at latency and throughput. > > Use the IOVA alloc, link, and sync APIs for DRM pagemap, which create DMA > mappings between the CPU and GPU for copying data. > > Signed-off-by: Matthew Brost <[email protected]> > > --- > v5: > - Remove extra newline (Thomas) > - Adjust alignemnt calculation (Thomas) > --- > drivers/gpu/drm/drm_pagemap.c | 83 +++++++++++++++++++++++++++++------ > 1 file changed, 69 insertions(+), 14 deletions(-) > > diff --git a/drivers/gpu/drm/drm_pagemap.c b/drivers/gpu/drm/drm_pagemap.c > index ef8b9c69d1d4..d9fceffce347 100644 > --- a/drivers/gpu/drm/drm_pagemap.c > +++ b/drivers/gpu/drm/drm_pagemap.c > @@ -281,6 +281,19 @@ drm_pagemap_migrate_map_device_private_pages(struct > device *dev, > return 0; > } > > +/** > + * struct drm_pagemap_iova_state - DRM pagemap IOVA state > + * @dma_state: DMA IOVA state. > + * @offset: Current offset in IOVA. > + * > + * This structure acts as an iterator for packing all IOVA addresses within a > + * contiguous range. > + */ > +struct drm_pagemap_iova_state { > + struct dma_iova_state dma_state; > + unsigned long offset; > +}; > + > /** > * drm_pagemap_migrate_map_system_pages() - Map system or device coherent > * migration pages for GPU SVM migration > @@ -289,6 +302,7 @@ drm_pagemap_migrate_map_device_private_pages(struct > device *dev, > * @migrate_pfn: Array of page frame numbers of system pages or peer pages > to map. > * @npages: Number of system or device coherent pages to map. > * @dir: Direction of data transfer (e.g., DMA_BIDIRECTIONAL) > + * @state: DMA IOVA state for mapping. > * > * This function maps pages of memory for migration usage in GPU SVM. It > * iterates over each page frame number provided in @migrate_pfn, maps the Not visible in this diff but we should update the doc as the return value is not only 0 or -EFAULT, it can be any error code returned by dma_iova_link(). > @@ -302,9 +316,11 @@ drm_pagemap_migrate_map_system_pages(struct device *dev, > struct drm_pagemap_addr *pagemap_addr, > unsigned long *migrate_pfn, > unsigned long npages, > - enum dma_data_direction dir) > + enum dma_data_direction dir, > + struct drm_pagemap_iova_state *state) > { > unsigned long i; > + bool try_alloc = false; > > for (i = 0; i < npages;) { > struct page *page = migrate_pfn_to_page(migrate_pfn[i]); > @@ -319,9 +335,31 @@ drm_pagemap_migrate_map_system_pages(struct device *dev, > folio = page_folio(page); > order = folio_order(folio); > > - dma_addr = dma_map_page(dev, page, 0, page_size(page), dir); > - if (dma_mapping_error(dev, dma_addr)) > - return -EFAULT; > + if (!try_alloc) { > + dma_iova_try_alloc(dev, &state->dma_state, > + (npages - i) * PAGE_SIZE >= > + HPAGE_PMD_SIZE ? > + HPAGE_PMD_SIZE : 0, > + npages * PAGE_SIZE); > + try_alloc = true; > + } > + > + if (dma_use_iova(&state->dma_state)) { > + int err = dma_iova_link(dev, &state->dma_state, > + page_to_phys(page), > + state->offset, page_size(page), > + dir, 0); > + if (err) > + return err; > + > + dma_addr = state->dma_state.addr + state->offset; > + state->offset += page_size(page); > + } else { > + dma_addr = dma_map_page(dev, page, 0, page_size(page), > + dir); > + if (dma_mapping_error(dev, dma_addr)) > + return -EFAULT; > + } > > pagemap_addr[i] = > drm_pagemap_addr_encode(dma_addr, > @@ -332,6 +370,9 @@ drm_pagemap_migrate_map_system_pages(struct device *dev, > i += NR_PAGES(order); > } > > + if (dma_use_iova(&state->dma_state)) > + return dma_iova_sync(dev, &state->dma_state, 0, state->offset); > + > return 0; > } > > @@ -343,6 +384,7 @@ drm_pagemap_migrate_map_system_pages(struct device *dev, > * @pagemap_addr: Array of DMA information corresponding to mapped pages > * @npages: Number of pages to unmap > * @dir: Direction of data transfer (e.g., DMA_BIDIRECTIONAL) > + * @state: DMA IOVA state for mapping. > * > * This function unmaps previously mapped pages of memory for GPU Shared > Virtual > * Memory (SVM). It iterates over each DMA address provided in @dma_addr, > checks While we are here: s/@dma_addr/@pagemap_addr/ Francois > @@ -352,10 +394,17 @@ static void drm_pagemap_migrate_unmap_pages(struct > device *dev, > struct drm_pagemap_addr > *pagemap_addr, > unsigned long *migrate_pfn, > unsigned long npages, > - enum dma_data_direction dir) > + enum dma_data_direction dir, > + struct drm_pagemap_iova_state > *state) > { > unsigned long i; > > + if (state && dma_use_iova(&state->dma_state)) { > + dma_iova_unlink(dev, &state->dma_state, 0, state->offset, dir, > 0); > + dma_iova_free(dev, &state->dma_state); > + return; > + } > + > for (i = 0; i < npages;) { > struct page *page = migrate_pfn_to_page(migrate_pfn[i]); > > @@ -410,7 +459,7 @@ drm_pagemap_migrate_remote_to_local(struct > drm_pagemap_devmem *devmem, > devmem->pre_migrate_fence); > out: > drm_pagemap_migrate_unmap_pages(remote_device, pagemap_addr, local_pfns, > - npages, DMA_FROM_DEVICE); > + npages, DMA_FROM_DEVICE, NULL); > return err; > } > > @@ -420,11 +469,13 @@ drm_pagemap_migrate_sys_to_dev(struct > drm_pagemap_devmem *devmem, > struct page *local_pages[], > struct drm_pagemap_addr pagemap_addr[], > unsigned long npages, > - const struct drm_pagemap_devmem_ops *ops) > + const struct drm_pagemap_devmem_ops *ops, > + struct drm_pagemap_iova_state *state) > { > int err = drm_pagemap_migrate_map_system_pages(devmem->dev, > pagemap_addr, sys_pfns, > - npages, DMA_TO_DEVICE); > + npages, DMA_TO_DEVICE, > + state); > > if (err) > goto out; > @@ -433,7 +484,7 @@ drm_pagemap_migrate_sys_to_dev(struct drm_pagemap_devmem > *devmem, > devmem->pre_migrate_fence); > out: > drm_pagemap_migrate_unmap_pages(devmem->dev, pagemap_addr, sys_pfns, > npages, > - DMA_TO_DEVICE); > + DMA_TO_DEVICE, state); > return err; > } > > @@ -461,6 +512,7 @@ static int drm_pagemap_migrate_range(struct > drm_pagemap_devmem *devmem, > const struct migrate_range_loc *cur, > const struct drm_pagemap_migrate_details > *mdetails) > { > + struct drm_pagemap_iova_state state = {}; > int ret = 0; > > if (cur->start == 0) > @@ -488,7 +540,7 @@ static int drm_pagemap_migrate_range(struct > drm_pagemap_devmem *devmem, > &pages[last->start], > &pagemap_addr[last->start], > cur->start - last->start, > - last->ops); > + last->ops, &state); > > out: > *last = *cur; > @@ -993,6 +1045,7 @@ EXPORT_SYMBOL(drm_pagemap_put); > int drm_pagemap_evict_to_ram(struct drm_pagemap_devmem *devmem_allocation) > { > const struct drm_pagemap_devmem_ops *ops = devmem_allocation->ops; > + struct drm_pagemap_iova_state state = {}; > unsigned long npages, mpages = 0; > struct page **pages; > unsigned long *src, *dst; > @@ -1034,7 +1087,7 @@ int drm_pagemap_evict_to_ram(struct drm_pagemap_devmem > *devmem_allocation) > err = drm_pagemap_migrate_map_system_pages(devmem_allocation->dev, > pagemap_addr, > dst, npages, > - DMA_FROM_DEVICE); > + DMA_FROM_DEVICE, &state); > if (err) > goto err_finalize; > > @@ -1051,7 +1104,7 @@ int drm_pagemap_evict_to_ram(struct drm_pagemap_devmem > *devmem_allocation) > migrate_device_pages(src, dst, npages); > migrate_device_finalize(src, dst, npages); > drm_pagemap_migrate_unmap_pages(devmem_allocation->dev, pagemap_addr, > dst, npages, > - DMA_FROM_DEVICE); > + DMA_FROM_DEVICE, &state); > > err_free: > kvfree(buf); > @@ -1095,6 +1148,7 @@ static int __drm_pagemap_migrate_to_ram(struct > vm_area_struct *vas, > MIGRATE_VMA_SELECT_DEVICE_COHERENT, > .fault_page = page, > }; > + struct drm_pagemap_iova_state state = {}; > struct drm_pagemap_zdd *zdd; > const struct drm_pagemap_devmem_ops *ops; > struct device *dev = NULL; > @@ -1154,7 +1208,7 @@ static int __drm_pagemap_migrate_to_ram(struct > vm_area_struct *vas, > > err = drm_pagemap_migrate_map_system_pages(dev, pagemap_addr, > migrate.dst, npages, > - DMA_FROM_DEVICE); > + DMA_FROM_DEVICE, &state); > if (err) > goto err_finalize; > > @@ -1172,7 +1226,8 @@ static int __drm_pagemap_migrate_to_ram(struct > vm_area_struct *vas, > migrate_vma_finalize(&migrate); > if (dev) > drm_pagemap_migrate_unmap_pages(dev, pagemap_addr, migrate.dst, > - npages, DMA_FROM_DEVICE); > + npages, DMA_FROM_DEVICE, > + &state); > err_free: > kvfree(buf); > err_out: > -- > 2.34.1 >
