On Thu, Jan 30, 2025 at 07:51:49PM +0100, Thomas Hellström wrote: > On Thu, 2025-01-30 at 09:31 -0800, Matthew Brost wrote: > > On Thu, Jan 30, 2025 at 04:56:39PM +0000, Matthew Auld wrote: > > > On 30/01/2025 16:32, Matthew Brost wrote: > > > > On Thu, Jan 30, 2025 at 02:22:55PM +0000, Matthew Auld wrote: > > > > > On 29/01/2025 19:52, Matthew Brost wrote: > > > > > > Migration is implemented with range granularity, with VRAM > > > > > > backing being > > > > > > a VM private TTM BO (i.e., shares dma-resv with VM). The > > > > > > lifetime of the > > > > > > TTM BO is limited to when the SVM range is in VRAM (i.e., > > > > > > when a VRAM > > > > > > SVM range is migrated to SRAM, the TTM BO is destroyed). > > > > > > > > > > > > The design choice for using TTM BO for VRAM backing store, as > > > > > > opposed to > > > > > > direct buddy allocation, is as follows: > > > > > > > > > > > > - DRM buddy allocations are not at page granularity, offering > > > > > > no > > > > > > advantage over a BO. > > > > > > - Unified eviction is required (SVM VRAM and TTM BOs need to > > > > > > be able to > > > > > > evict each other). > > > > > > - For exhaustive eviction [1], SVM VRAM allocations will > > > > > > almost certainly > > > > > > require a dma-resv. > > > > > > - Likely allocation size is 2M which makes of size of BO > > > > > > (872) > > > > > > acceptable per allocation (872 / 2M == .0004158). > > > > > > > > > > > > With this, using TTM BO for VRAM backing store seems to be an > > > > > > obvious > > > > > > choice as it allows leveraging of the TTM eviction code. > > > > > > > > > > > > Current migration policy is migrate any SVM range greater > > > > > > than or equal > > > > > > to 64k once. > > > > > > > > > > > > [1] https://patchwork.freedesktop.org/series/133643/ > > > > > > > > > > > > v2: > > > > > > - Rebase on latest GPU SVM > > > > > > - Retry page fault on get pages returning mixed allocation > > > > > > - Use drm_gpusvm_devmem > > > > > > v3: > > > > > > - Use new BO flags > > > > > > - New range structure (Thomas) > > > > > > - Hide migration behind Kconfig > > > > > > - Kernel doc (Thomas) > > > > > > - Use check_pages_threshold > > > > > > v4: > > > > > > - Don't evict partial unmaps in garbage collector (Thomas) > > > > > > - Use %pe to print errors (Thomas) > > > > > > - Use %p to print pointers (Thomas) > > > > > > > > > > > > Signed-off-by: Matthew Brost <matthew.brost@xxxxxxxxx> > > > > > > --- > > > > > > drivers/gpu/drm/xe/xe_svm.c | 99 > > > > > > +++++++++++++++++++++++++++++++++++-- > > > > > > drivers/gpu/drm/xe/xe_svm.h | 5 ++ > > > > > > 2 files changed, 100 insertions(+), 4 deletions(-) > > > > > > > > > > > > diff --git a/drivers/gpu/drm/xe/xe_svm.c > > > > > > b/drivers/gpu/drm/xe/xe_svm.c > > > > > > index ba1db030bf33..fc030855d078 100644 > > > > > > --- a/drivers/gpu/drm/xe/xe_svm.c > > > > > > +++ b/drivers/gpu/drm/xe/xe_svm.c > > > > > > @@ -502,7 +502,6 @@ static int > > > > > > xe_svm_populate_devmem_pfn(struct drm_gpusvm_devmem > > > > > > *devmem_allocatio > > > > > > return 0; > > > > > > } > > > > > > -__maybe_unused > > > > > > static const struct drm_gpusvm_devmem_ops > > > > > > gpusvm_devmem_ops = { > > > > > > .devmem_release = xe_svm_devmem_release, > > > > > > .populate_devmem_pfn = xe_svm_populate_devmem_pfn, > > > > > > @@ -582,6 +581,64 @@ static bool xe_svm_range_is_valid(struct > > > > > > xe_svm_range *range, > > > > > > return (range->tile_present & ~range- > > > > > > >tile_invalidated) & BIT(tile->id); > > > > > > } > > > > > > +static struct xe_mem_region *tile_to_mr(struct xe_tile > > > > > > *tile) > > > > > > +{ > > > > > > + return &tile->mem.vram; > > > > > > +} > > > > > > + > > > > > > +static struct xe_bo *xe_svm_alloc_vram(struct xe_vm *vm, > > > > > > struct xe_tile *tile, > > > > > > + struct xe_svm_range > > > > > > *range, > > > > > > + const struct > > > > > > drm_gpusvm_ctx *ctx) > > > > > > +{ > > > > > > + struct xe_mem_region *mr = tile_to_mr(tile); > > > > > > + struct drm_buddy_block *block; > > > > > > + struct list_head *blocks; > > > > > > + struct xe_bo *bo; > > > > > > + ktime_t end = 0; > > > > > > + int err; > > > > > > + > > > > > > +retry: > > > > > > + xe_vm_lock(vm, false); > > > > > > + bo = xe_bo_create(tile_to_xe(tile), tile, vm, range- > > > > > > >base.itree.last + 1 - > > > > > > + range->base.itree.start, > > > > > > ttm_bo_type_device, > > > > > > + XE_BO_FLAG_VRAM_IF_DGFX(tile) | > > > > > > + XE_BO_FLAG_CPU_ADDR_MIRROR); > > > > > > + xe_vm_unlock(vm); > > > > > > > > > > What was the trick again to ensure eviction is not triggered at > > > > > this point? > > > > > I thought there was some trick with eviction_valuable() but I > > > > > can't find it. > > > > > > > > > > > > > I dropped that given the hacky nature of how it was implemented. > > > > Yes, it > > > > is possible that we allocate VRAM and it is immediately evicted > > > > before > > > > the bind occurs but in practice should never really happen given > > > > this BO > > > > should be the last entry on the LRU list. Even if this happens, I > > > > believe this is harmless given the bind will abort and trigger a > > > > retry. > > > > > > Looking at xe_svm_bo_evict() it wants to use stuff like > > > bo->devmem_allocation, but that is not set up yet? For example > > > dereferencing the devmem_allocation->mm from there will potentially > > > hit a > > > NPD? > > > > Good catch. I think drm_gpusvm_devmem_init at least needs to be moved > > under BO's dma resv lock. > > > > The multi-GPU work Thomas is doing will even expand this scope > > further > > to include drm_gpusvm_migrate_to_devmem under the BO dma-resv too - > > this > > was ommitted in this series given we'd have to rework the mmap read > > lock > > a bit too which I'd prefer to wait on until his series. > > TBH, I think all pages need to be present in the CPU page-table before > we can release the dma-resv lock. That will ensure the eviction causes > an invalidation later than the migration invalidation, and everybody's > happy. > Yea, perhaps. Certainly this is safer but I think I reasoned it actually ok given 2 opposing migrate functions lock the individual pages before the migration actually happens. We'd likely end up hitting the retry in the eviction code though due to partial eviction. I do agree in general with taking dma-resv lock here for safety / simplicity. > An alternative until the multi-device series lands could be to pin the > bo until the end of the function. That would avoid the locking > trickiness. > I'd rather just rework the locking the structure with the mmap taken in the Xe layer + a comment indicating moving this lock to a DRM layer is preferred. Matt > /Thomas > > > > > Matt > > > > > > > > > > > > > Matt > > > > > > > > > > + if (IS_ERR(bo)) { > > > > > > + err = PTR_ERR(bo); > > > > > > + if (xe_vm_validate_should_retry(NULL, err, > > > > > > &end)) > > > > > > + goto retry; > > > > > > + return bo; > > > > > > + } > > > > > > + > > > > > > + drm_gpusvm_devmem_init(&bo->devmem_allocation, > > > > > > + vm->xe->drm.dev, vm- > > > > > > >svm.gpusvm.mm, > > > > > > + &gpusvm_devmem_ops, > > > > > > + &tile->mem.vram.dpagemap, > > > > > > + range->base.itree.last + 1 - > > > > > > + range->base.itree.start); > > > > > > + > > > > > > + blocks = &to_xe_ttm_vram_mgr_resource(bo- > > > > > > >ttm.resource)->blocks; > > > > > > + list_for_each_entry(block, blocks, link) > > > > > > + block->private = mr; > > > > > > + > > > > > > + /* > > > > > > + * Take ref because as soon as > > > > > > drm_gpusvm_migrate_to_devmem succeeds the > > > > > > + * creation ref can be dropped upon CPU fault or > > > > > > unmap. > > > > > > + */ > > > > > > + xe_bo_get(bo); > > > > > > + > > > > > > + err = drm_gpusvm_migrate_to_devmem(&vm->svm.gpusvm, > > > > > > &range->base, > > > > > > + &bo- > > > > > > >devmem_allocation, ctx); > > > > > > + if (err) { > > > > > > + xe_bo_put(bo); /* Local ref */ > > > > > > + xe_bo_put(bo); /* Creation ref */ > > > > > > + return ERR_PTR(err); > > > > > > + } > > > > > > + > > > > > > + return bo; > > > > > > +} > > > > > > + > > > > > > /** > > > > > > * xe_svm_handle_pagefault() - SVM handle page fault > > > > > > * @vm: The VM. > > > > > > @@ -590,7 +647,8 @@ static bool xe_svm_range_is_valid(struct > > > > > > xe_svm_range *range, > > > > > > * @fault_addr: The GPU fault address. > > > > > > * @atomic: The fault atomic access bit. > > > > > > * > > > > > > - * Create GPU bindings for a SVM page fault. > > > > > > + * Create GPU bindings for a SVM page fault. Optionally > > > > > > migrate to device > > > > > > + * memory. > > > > > > * > > > > > > * Return: 0 on success, negative error code on error. > > > > > > */ > > > > > > @@ -598,11 +656,18 @@ int xe_svm_handle_pagefault(struct > > > > > > xe_vm *vm, struct xe_vma *vma, > > > > > > struct xe_tile *tile, u64 > > > > > > fault_addr, > > > > > > bool atomic) > > > > > > { > > > > > > - struct drm_gpusvm_ctx ctx = { .read_only = > > > > > > xe_vma_read_only(vma), }; > > > > > > + struct drm_gpusvm_ctx ctx = { > > > > > > + .read_only = xe_vma_read_only(vma), > > > > > > + .devmem_possible = IS_DGFX(vm->xe) && > > > > > > + IS_ENABLED(CONFIG_DRM_XE_DEVMEM_MIRR > > > > > > OR), > > > > > > + .check_pages_threshold = IS_DGFX(vm->xe) && > > > > > > + IS_ENABLED(CONFIG_DRM_XE_DEVMEM_MIRR > > > > > > OR) ? SZ_64K : 0, > > > > > > + }; > > > > > > struct xe_svm_range *range; > > > > > > struct drm_gpusvm_range *r; > > > > > > struct drm_exec exec; > > > > > > struct dma_fence *fence; > > > > > > + struct xe_bo *bo = NULL; > > > > > > ktime_t end = 0; > > > > > > int err; > > > > > > @@ -610,6 +675,9 @@ int xe_svm_handle_pagefault(struct xe_vm > > > > > > *vm, struct xe_vma *vma, > > > > > > xe_assert(vm->xe, xe_vma_is_cpu_addr_mirror(vma)); > > > > > > retry: > > > > > > + xe_bo_put(bo); > > > > > > + bo = NULL; > > > > > > + > > > > > > /* Always process UNMAPs first so view SVM ranges is > > > > > > current */ > > > > > > err = xe_svm_garbage_collector(vm); > > > > > > if (err) > > > > > > @@ -625,9 +693,31 @@ int xe_svm_handle_pagefault(struct xe_vm > > > > > > *vm, struct xe_vma *vma, > > > > > > if (xe_svm_range_is_valid(range, tile)) > > > > > > return 0; > > > > > > + /* XXX: Add migration policy, for now migrate range > > > > > > once */ > > > > > > + if (!range->migrated && range- > > > > > > >base.flags.migrate_devmem && > > > > > > + (range->base.itree.last + 1 - range- > > > > > > >base.itree.start) >= SZ_64K) { > > > > > > + range->migrated = true; > > > > > > + > > > > > > + bo = xe_svm_alloc_vram(vm, tile, range, > > > > > > &ctx); > > > > > > + if (IS_ERR(bo)) { > > > > > > + drm_info(&vm->xe->drm, > > > > > > + "VRAM allocation failed, > > > > > > falling back to retrying, asid=%u, errno %pe\n", > > > > > > + vm->usm.asid, bo); > > > > > > + bo = NULL; > > > > > > + goto retry; > > > > > > + } > > > > > > + } > > > > > > + > > > > > > err = drm_gpusvm_range_get_pages(&vm->svm.gpusvm, r, > > > > > > &ctx); > > > > > > - if (err == -EFAULT || err == -EPERM) /* Corner > > > > > > where CPU mappings have changed */ > > > > > > + /* Corner where CPU mappings have changed */ > > > > > > + if (err == -EOPNOTSUPP || err == -EFAULT || err == - > > > > > > EPERM) { > > > > > > + if (err == -EOPNOTSUPP) > > > > > > + drm_gpusvm_range_evict(&vm- > > > > > > >svm.gpusvm, &range->base); > > > > > > + drm_info(&vm->xe->drm, > > > > > > + "Get pages failed, falling back to > > > > > > retrying, asid=%u, gpusvm=%p, errno %pe\n", > > > > > > + vm->usm.asid, &vm->svm.gpusvm, > > > > > > ERR_PTR(err)); > > > > > > goto retry; > > > > > > + } > > > > > > if (err) > > > > > > goto err_out; > > > > > > @@ -658,6 +748,7 @@ int xe_svm_handle_pagefault(struct xe_vm > > > > > > *vm, struct xe_vma *vma, > > > > > > dma_fence_put(fence); > > > > > > err_out: > > > > > > + xe_bo_put(bo); > > > > > > return err; > > > > > > } > > > > > > diff --git a/drivers/gpu/drm/xe/xe_svm.h > > > > > > b/drivers/gpu/drm/xe/xe_svm.h > > > > > > index 63daffdfdbf6..4c2576162c39 100644 > > > > > > --- a/drivers/gpu/drm/xe/xe_svm.h > > > > > > +++ b/drivers/gpu/drm/xe/xe_svm.h > > > > > > @@ -35,6 +35,11 @@ struct xe_svm_range { > > > > > > * range. Protected by GPU SVM notifier lock. > > > > > > */ > > > > > > u8 tile_invalidated; > > > > > > + /** > > > > > > + * @migrated: Range has been migrated to device > > > > > > memory, protected by > > > > > > + * GPU fault handler locking. > > > > > > + */ > > > > > > + u8 migrated :1; > > > > > > }; > > > > > > int xe_devm_add(struct xe_tile *tile, struct xe_mem_region > > > > > > *mr); > > > > > > > > >
