[PATCH v5 27/32] drm/xe: Add SVM VRAM migration
Ghimiray, Himal Prasad
himal.prasad.ghimiray at intel.com
Wed Feb 19 03:40:26 UTC 2025
On 19-02-2025 08:35, Matthew Brost wrote:
> On Wed, Feb 19, 2025 at 08:29:53AM +0530, Ghimiray, Himal Prasad wrote:
>>
>>
>> On 19-02-2025 03:24, Matthew Brost wrote:
>>> On Thu, Feb 13, 2025 at 11:58:27PM +0530, Ghimiray, Himal Prasad wrote:
>>>>
>>>>
>>>> On 13-02-2025 07:41, 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)
>>>>> v5:
>>>>> - Use range size helper (Thomas)
>>>>> - Make BO external (Thomas)
>>>>> - Set tile to NULL for BO creation (Thomas)
>>>>> - Drop BO mirror flag (Thomas)
>>>>> - Hold BO dma-resv lock across migration (Auld, Thomas)
>>>>>
>>>>> Signed-off-by: Matthew Brost <matthew.brost at intel.com>
>>>>> ---
>>>>> drivers/gpu/drm/xe/xe_svm.c | 111 ++++++++++++++++++++++++++++++++++--
>>>>> drivers/gpu/drm/xe/xe_svm.h | 5 ++
>>>>> 2 files changed, 112 insertions(+), 4 deletions(-)
>>>>>
>>>>> diff --git a/drivers/gpu/drm/xe/xe_svm.c b/drivers/gpu/drm/xe/xe_svm.c
>>>>> index 0a78a838508c..2e1e0f31c1a8 100644
>>>>> --- a/drivers/gpu/drm/xe/xe_svm.c
>>>>> +++ b/drivers/gpu/drm/xe/xe_svm.c
>>>>> @@ -32,6 +32,11 @@ static unsigned long xe_svm_range_end(struct xe_svm_range *range)
>>>>> return drm_gpusvm_range_end(&range->base);
>>>>> }
>>>>> +static unsigned long xe_svm_range_size(struct xe_svm_range *range)
>>>>> +{
>>>>> + return drm_gpusvm_range_size(&range->base);
>>>>> +}
>>>>> +
>>>>> static void *xe_svm_devm_owner(struct xe_device *xe)
>>>>> {
>>>>> return xe;
>>>>> @@ -512,7 +517,6 @@ 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,
>>>>> @@ -592,6 +596,71 @@ 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_vram_region *tile_to_vr(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 mm_struct *mm = vm->svm.gpusvm.mm;
>>>>> + struct xe_vram_region *vr = tile_to_vr(tile);
>>>>> + struct drm_buddy_block *block;
>>>>> + struct list_head *blocks;
>>>>> + struct xe_bo *bo;
>>>>> + ktime_t end = 0;
>>>>> + int err;
>>>>> +
>>>>> + if (!mmget_not_zero(mm))
>>>>> + return ERR_PTR(-EFAULT);
>>>>> + mmap_read_lock(mm);
>>>>> +
>>>>> +retry:
>>>>> + bo = xe_bo_create_locked(tile_to_xe(tile), NULL, NULL,
>>>>> + xe_svm_range_size(range),
>>>>> + ttm_bo_type_device,
>>>>> + XE_BO_FLAG_VRAM_IF_DGFX(tile));
>>>>> + if (IS_ERR(bo)) {
>>>>> + err = PTR_ERR(bo);
>>>>> + if (xe_vm_validate_should_retry(NULL, err, &end))
>>>>> + goto retry;
>>>>> + goto unlock;
>>>>> + }
>>>>> +
>>>>> + drm_gpusvm_devmem_init(&bo->devmem_allocation,
>>>>> + vm->xe->drm.dev, mm,
>>>>> + &gpusvm_devmem_ops,
>>>>> + &tile->mem.vram.dpagemap,
>>>>> + xe_svm_range_size(range));
>>>>> +
>>>>> + blocks = &to_xe_ttm_vram_mgr_resource(bo->ttm.resource)->blocks;
>>>>> + list_for_each_entry(block, blocks, link)
>>>>> + block->private = vr;
>>>>> +
>>>>> + /*
>>>>> + * 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);
>>>>> + xe_bo_unlock(bo);
>>>>> + if (err) {
>>>>> + xe_bo_put(bo); /* Local ref */
>>>>> + xe_bo_put(bo); /* Creation ref */
>>>>> + bo = ERR_PTR(err);
>>>>> + }
>>>>> +
>>>>> +unlock:
>>>>> + mmap_read_unlock(mm);
>>>>> + mmput(mm);
>>>>> +
>>>>> + return bo;
>>>>> +}
>>>>> +
>>>>> /**
>>>>> * xe_svm_handle_pagefault() - SVM handle page fault
>>>>> * @vm: The VM.
>>>>> @@ -600,7 +669,8 @@ 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.
>>>>> */
>>>>> @@ -608,11 +678,18 @@ 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_MIRROR),
>>>>> + .check_pages_threshold = IS_DGFX(vm->xe) &&
>>>>> + IS_ENABLED(CONFIG_DRM_XE_DEVMEM_MIRROR) ? 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;
>>>>> @@ -620,6 +697,9 @@ 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)
>>>>> @@ -635,9 +715,31 @@ 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 &&
>>>>> + xe_svm_range_size(range) >= SZ_64K) {
>>>>> + range->migrated = true;
>>>>
>>>>
>>>> shouldn't this be set to true, only once xe_svm_alloc_vram is successfull ?
>>>> In case of bo alloc failure retry wont enter here.
>>>>
>>>
>>> No. The point of this is try to migrate once to avoid a live lock case
>>> of concurrent CPU and GPU access. Once we have migration policy, I'd
>>> suspect memory marked as prefered VRAM only try once too. If memory is
>>> marked as VRAM only we'd retry to a limit and if reached kill the app.
>>> We can work of those details when that code lands. Until then, trying
>>> once seems reasonable.
>>
>> I understand what we are trying to achieve here, and it functions well.
>> However, my only concern is member name "migrated" gives the impression that
>> it will be set to true only if the range has been successfully migrated to
>> VRAM.
>>
>
> s/migrated/skip_migrate ?
sounds good to me.
>
>>>
>>> Matt
>>>
>>>>> +
>>>>> + 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);
>>
>> This log is also misleading, we dont retry vram allocation in case of first
>> failure.
>>
>
> How about...
>
> "VRAM allocation failed, falling back to retrying fault,"
Yup.
>
> Matt
>
>>>>> + 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;
>>>>> @@ -668,6 +770,7 @@ 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 0fa525d34987..984a61651d9e 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.
>>
>> The range is not necessarily migrated to device memory if migrated is true.
>>
>>>>> + */
>>>>> + u8 migrated :1;
>>>>> };
>>>>> int xe_devm_add(struct xe_tile *tile, struct xe_vram_region *vr);
>>>>
>>
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