[PATCH v3] drm/amdkfd: Use partial migrations in GPU page faults
Chen, Xiaogang
xiaogang.chen at amd.com
Fri Sep 29 20:24:32 UTC 2023
On 9/29/2023 2:48 PM, Felix Kuehling wrote:
>
> On 2023-09-29 15:44, Chen, Xiaogang wrote:
>>
>> On 9/29/2023 1:41 PM, Felix Kuehling wrote:
>>>
>>> On 2023-09-29 14:25, Chen, Xiaogang wrote:
>>>>
>>>> On 9/28/2023 4:26 PM, Felix Kuehling wrote:
>>>>> On 2023-09-20 13:32, Xiaogang.Chen wrote:
>>>>>> From: Xiaogang Chen <xiaogang.chen at amd.com>
>>>>>>
>>>>>> This patch implements partial migration in gpu page fault
>>>>>> according to migration
>>>>>> granularity(default 2MB) and not split svm range in cpu page
>>>>>> fault handling.
>>>>>> A svm range may include pages from both system ram and vram of
>>>>>> one gpu now.
>>>>>> These chagnes are expected to improve migration performance and
>>>>>> reduce mmu
>>>>>> callback and TLB flush workloads.
>>>>>>
>>>>>> Signed-off-by: xiaogang chen<xiaogang.chen at amd.com>
>>>>>
>>>>> Some more nit-picks inline.
>>> [snip]
>>>>> @@ -202,12 +200,24 @@ svm_range_dma_map_dev(struct amdgpu_device
>>>>> *adev, struct svm_range *prange,
>>>>> static int
>>>>> svm_range_dma_map(struct svm_range *prange, unsigned long *bitmap,
>>>>> unsigned long offset, unsigned long npages,
>>>>> - unsigned long *hmm_pfns)
>>>>> + unsigned long *hmm_pfns, uint64_t *vram_pages)
>>>>> {
>>>>> struct kfd_process *p;
>>>>> uint32_t gpuidx;
>>>>> + struct page **page;
>>>>> int r;
>>>>> + page = kvcalloc(npages, sizeof(*page), GFP_KERNEL);
>>>>>
>>>>> Is there a reason this needs to be 0-initialized? The loop below
>>>>> initializes all elements.
>>>> Will use kvmalloc_array instead. This array is not needed to init
>>>> during alloc as it will be set afterword.
>>>>>
>>>>> I'm also not happy about having to allocate this page array here.
>>>>> It may be justified if the repeated calls to hmm_pfn_to_page were
>>>>> expensive compared to the memory allocation and initialization.
>>>>> I'm not convinced that's the case, though. With
>>>>> CONFIG_SPARSEMEM_VMEMMAP, hmm_pfn_to_page basically boils down to
>>>>> __pfn_to_page, which is a macro that does just this:
>>>>>
>>>>> #define __pfn_to_page(pfn) (vmemmap + (pfn))
>>>>>
>>>>> See
>>>>> https://elixir.bootlin.com/linux/v6.5.5/source/include/asm-generic/memory_model.h#L37.
>>>>>
>>>> We get page* array here, then we do not need get page at
>>>> svm_range_dma_map_dev for each device since pages are same for all
>>>> gpu devices. So we save calling hmm_pfn_to_page though calling
>>>> hmm_pfn_to_page cost is low. Here we also want get vram page number
>>>> during svm_range_dma_map.
>>>>
>>>> I think you do not want alloc a page array each time we do
>>>> svm_range_dma_map? then can we put this struct page **page at
>>>> svm_range, and alloc it each time create new prange(and clone/split
>>>> prange)?
>>>
>>> Allocating and freeing memory in every dmamap call adds a point of
>>> failure and non-deterministic overhead for the memory allocation.
>>> It's non-deterministic because it depends on current memory pressure
>>> situation and if the array is large, it also needs to update the
>>> kernel page table and potentially flush CPU TLBs.
>>>
>>> Allocating the page pointer array permanently in the prange
>>> structure would be even worse, because that increases our system
>>> memory overhead. For each GB of virtual address space we manage, we
>>> waste 2MB of system memory for the page arrays. To make matters
>>> worse, those page arrays are allocated in kernel mode where they are
>>> not swappable. It's like taking physical DIMM sticks out of your
>>> system. We worked hard to eliminate redundant address and page array
>>> allocations from the driver a few years ago.
>>>
>>> I'd prefer a small amount of redundant address calculations over the
>>> memory or non-deterministic allocation overhead.
>>>
>> Then I think we can cal vram_pages atsvm_range_validate_and_map as
>> the last version:
>>
>> +for (int i = 0; i < npages; i++) {
>>
>> +if (is_zone_device_page(hmm_pfn_to_page(hmm_range->hmm_pfns[i])))
>>
>> vram_pages++;
>>
>> +}
>>
>> That will not alloc page* array, but have additional calling
>> hmm_pfn_to_page.
>>
>> Or add a parameter at svm_range_dma_map_dev to indicate whether cal
>> vram_pages, and only one svm_range_dma_map_dev call will cal vram_pages.
>
> svm_range_dma_map_dev has the
> is_zone_device_page(hmm_pfn_to_page(...)) check already. Always
> counting VRAM pages in svm_range_dma_map_dev would be trivial. Adding
> a condition would only make it slower.
>
> Whether or not use use the vram_pages count in the end is a different
> matter. But I think just unconditionally adding vram_pages++ in
> svm_range_dma_map_dev would have negligible overhead.
ok, adding a check at svm_range_dma_map_dev would spoil code cache or
branch prediction. Always do vram_pages++ even though get same result
for all gpu devices.
Regards
Xiaogang
>
> Regards,
> Felix
>
>
>>
>> Regards
>>
>> Xiaogang
>>
>>> Regards,
>>> Felix
>>>
>>>
>>>>
>>>>>
>>>>>> + if (!page)
>>>>>> + return -ENOMEM;
>>>>>> +
>>>>>> + *vram_pages = 0;
>>>>>> + for (int i = 0; i < npages; i++) {
>>>>>> + page[i] = hmm_pfn_to_page(hmm_pfns[i]);
>>>>>> + if (is_zone_device_page(page[i]))
>>>>>> + (*vram_pages)++;
>>>>>> + }
>>>>>> +
>>>>>> p = container_of(prange->svms, struct kfd_process, svms);
>>>>>> for_each_set_bit(gpuidx, bitmap, MAX_GPU_INSTANCE) {
>>>>>> @@ -221,11 +231,12 @@ svm_range_dma_map(struct svm_range *prange,
>>>>>> unsigned long *bitmap,
>>>>>> }
>>>>>> r = svm_range_dma_map_dev(pdd->dev->adev, prange,
>>>>>> offset, npages,
>>>>>> - hmm_pfns, gpuidx);
>>>>>> + hmm_pfns, gpuidx, page);
>>>>>> if (r)
>>>>>> break;
>>>>>> }
>>>>>> + kvfree(page);
>>>>>> return r;
>>>>>> }
>>>>>> @@ -347,6 +358,7 @@ svm_range *svm_range_new(struct
>>>>>> svm_range_list *svms, uint64_t start,
>>>>>> INIT_LIST_HEAD(&prange->child_list);
>>>>>> atomic_set(&prange->invalid, 0);
>>>>>> prange->validate_timestamp = 0;
>>>>>> + prange->vram_pages = 0;
>>>>>> mutex_init(&prange->migrate_mutex);
>>>>>> mutex_init(&prange->lock);
>>>>>> @@ -393,6 +405,8 @@ static void svm_range_bo_release(struct
>>>>>> kref *kref)
>>>>>> prange->start, prange->last);
>>>>>> mutex_lock(&prange->lock);
>>>>>> prange->svm_bo = NULL;
>>>>>> + /* prange does not hold vram page now */
>>>>>> + prange->actual_loc = 0;
>>>>>
>>>>> If you need this here, something probably went wrong elsewhere.
>>>>> Before we release the BO, we should have migrated everything to
>>>>> system memory, and actual_loc should already be 0. If anything,
>>>>> I'd add a WARN_ON(prange->actual_loc) here.
>>>>>
>>>> Will replace by WARN_ON as mentioned before.
>>>>>
>>>>>> mutex_unlock(&prange->lock);
>>>>>> spin_lock(&svm_bo->list_lock);
>>>>>> @@ -966,6 +980,11 @@ svm_range_split_nodes(struct svm_range *new,
>>>>>> struct svm_range *old,
>>>>>> new->svm_bo = svm_range_bo_ref(old->svm_bo);
>>>>>> new->ttm_res = old->ttm_res;
>>>>>> + /* set new's vram_pages as old range's now, the acurate
>>>>>> vram_pages
>>>>>> + * will be updated during mapping
>>>>>> + */
>>>>>> + new->vram_pages = min(old->vram_pages, new->npages);
>>>>>> +
>>>>>> spin_lock(&new->svm_bo->list_lock);
>>>>>> list_add(&new->svm_bo_list, &new->svm_bo->range_list);
>>>>>> spin_unlock(&new->svm_bo->list_lock);
>>>>>> @@ -1610,6 +1629,7 @@ static int
>>>>>> svm_range_validate_and_map(struct mm_struct *mm,
>>>>>> struct svm_validate_context *ctx;
>>>>>> unsigned long start, end, addr;
>>>>>> struct kfd_process *p;
>>>>>> + uint64_t vram_pages;
>>>>>> void *owner;
>>>>>> int32_t idx;
>>>>>> int r = 0;
>>>>>> @@ -1678,11 +1698,13 @@ static int
>>>>>> svm_range_validate_and_map(struct mm_struct *mm,
>>>>>> }
>>>>>> }
>>>>>> + vram_pages = 0;
>>>>>> start = prange->start << PAGE_SHIFT;
>>>>>> end = (prange->last + 1) << PAGE_SHIFT;
>>>>>> for (addr = start; addr < end && !r; ) {
>>>>>> struct hmm_range *hmm_range;
>>>>>> struct vm_area_struct *vma;
>>>>>> + uint64_t vram_pages_vma;
>>>>>> unsigned long next;
>>>>>> unsigned long offset;
>>>>>> unsigned long npages;
>>>>>> @@ -1711,12 +1733,14 @@ static int
>>>>>> svm_range_validate_and_map(struct mm_struct *mm,
>>>>>> offset = (addr - start) >> PAGE_SHIFT;
>>>>>> r = svm_range_dma_map(prange, ctx->bitmap, offset, npages,
>>>>>> - hmm_range->hmm_pfns);
>>>>>> + hmm_range->hmm_pfns, &vram_pages_vma);
>>>>>> if (r) {
>>>>>> pr_debug("failed %d to dma map range\n", r);
>>>>>> goto unreserve_out;
>>>>>> }
>>>>>> + vram_pages += vram_pages_vma;
>>>>>> +
>>>>>> svm_range_lock(prange);
>>>>>> if (amdgpu_hmm_range_get_pages_done(hmm_range)) {
>>>>>> pr_debug("hmm update the range, need validate
>>>>>> again\n");
>>>>>> @@ -1738,8 +1762,20 @@ static int
>>>>>> svm_range_validate_and_map(struct mm_struct *mm,
>>>>>> addr = next;
>>>>>> }
>>>>>> - if (addr == end)
>>>>>> + if (addr == end) {
>>>>>> prange->mapped_to_gpu = true;
>>>>>> + prange->vram_pages = vram_pages;
>>>>>> +
>>>>>> + /* if pragne does not include any vram page and it
>>>>>
>>>>> Typo: prange
>>>>>
>>>> ok.
>>>>>
>>>>>> + * has not released svm_bo drop its svm_bo reference
>>>>>> + */
>>>>>> + if (!vram_pages && prange->ttm_res) {
>>>>>> + svm_range_vram_node_free(prange);
>>>>>> + mutex_lock(&prange->lock);
>>>>>
>>>>> Is this lock really needed.
>>>>>
>>>> same as before, will remove mutex_lock/unlock(&prange->lock) as it
>>>> seems overprotected.
>>>>>
>>>>>> + prange->actual_loc = 0;
>>>>>> + mutex_unlock(&prange->lock);
>>>>>> + }
>>>>>> + }
>>>>>> unreserve_out:
>>>>>> svm_range_unreserve_bos(ctx);
>>>>>> @@ -1996,6 +2032,7 @@ static struct svm_range
>>>>>> *svm_range_clone(struct svm_range *old)
>>>>>> new->actual_loc = old->actual_loc;
>>>>>> new->granularity = old->granularity;
>>>>>> new->mapped_to_gpu = old->mapped_to_gpu;
>>>>>> + new->vram_pages = old->vram_pages;
>>>>>> bitmap_copy(new->bitmap_access, old->bitmap_access,
>>>>>> MAX_GPU_INSTANCE);
>>>>>> bitmap_copy(new->bitmap_aip, old->bitmap_aip,
>>>>>> MAX_GPU_INSTANCE);
>>>>>> @@ -2903,6 +2940,7 @@ svm_range_restore_pages(struct
>>>>>> amdgpu_device *adev, unsigned int pasid,
>>>>>> uint32_t vmid, uint32_t node_id,
>>>>>> uint64_t addr, bool write_fault)
>>>>>> {
>>>>>> + unsigned long start, last, size;
>>>>>> struct mm_struct *mm = NULL;
>>>>>> struct svm_range_list *svms;
>>>>>> struct svm_range *prange;
>>>>>> @@ -3038,32 +3076,38 @@ svm_range_restore_pages(struct
>>>>>> amdgpu_device *adev, unsigned int pasid,
>>>>>> kfd_smi_event_page_fault_start(node, p->lead_thread->pid,
>>>>>> addr,
>>>>>> write_fault, timestamp);
>>>>>> - if (prange->actual_loc != best_loc) {
>>>>>> + if (prange->actual_loc != 0 || best_loc != 0) {
>>>>>> migration = true;
>>>>>> + /* Align migration range start and size to granularity
>>>>>> size */
>>>>>> + size = 1UL << prange->granularity;
>>>>>> + start = ALIGN_DOWN(addr, size);
>>>>>> + last = ALIGN(addr + 1, size) - 1;
>>>>>> +
>>>>>> + start = (start >= prange->start) ? start : prange->start;
>>>>>> + last = (last <= prange->last) ? last : prange->last;
>>>>>
>>>>> Similar to the simplification I recommended in svm_migrate_to_ram,
>>>>> this could be:
>>>>>
>>>>> start = max(ALIGN_DOWN(addr, size), prange->start);
>>>>> last = min(ALIGN(addr + 1, size) - 1, prange->last);
>>>>>
>>>> ok, overlooked last time.
>>>>
>>>> Regards
>>>>
>>>> Xiaogang
>>>>
>>>>> Regards,
>>>>> Felix
>>>>>
>>>>>
>>>>>> +
>>>>>> if (best_loc) {
>>>>>> - r = svm_migrate_to_vram(prange, best_loc, mm,
>>>>>> - KFD_MIGRATE_TRIGGER_PAGEFAULT_GPU);
>>>>>> + r = svm_migrate_to_vram(prange, best_loc, start, last,
>>>>>> + mm, KFD_MIGRATE_TRIGGER_PAGEFAULT_GPU);
>>>>>> if (r) {
>>>>>> pr_debug("svm_migrate_to_vram failed (%d) at
>>>>>> %llx, falling back to system memory\n",
>>>>>> r, addr);
>>>>>> /* Fallback to system memory if migration to
>>>>>> * VRAM failed
>>>>>> */
>>>>>> - if (prange->actual_loc)
>>>>>> - r = svm_migrate_vram_to_ram(prange, mm,
>>>>>> - KFD_MIGRATE_TRIGGER_PAGEFAULT_GPU,
>>>>>> - NULL);
>>>>>> + if (prange->actual_loc && prange->actual_loc !=
>>>>>> best_loc)
>>>>>> + r = svm_migrate_vram_to_ram(prange, mm,
>>>>>> start, last,
>>>>>> + KFD_MIGRATE_TRIGGER_PAGEFAULT_GPU, NULL);
>>>>>> else
>>>>>> r = 0;
>>>>>> }
>>>>>> } else {
>>>>>> - r = svm_migrate_vram_to_ram(prange, mm,
>>>>>> - KFD_MIGRATE_TRIGGER_PAGEFAULT_GPU,
>>>>>> - NULL);
>>>>>> + r = svm_migrate_vram_to_ram(prange, mm, start, last,
>>>>>> + KFD_MIGRATE_TRIGGER_PAGEFAULT_GPU, NULL);
>>>>>> }
>>>>>> if (r) {
>>>>>> pr_debug("failed %d to migrate svms %p [0x%lx
>>>>>> 0x%lx]\n",
>>>>>> - r, svms, prange->start, prange->last);
>>>>>> + r, svms, start, last);
>>>>>> goto out_unlock_range;
>>>>>> }
>>>>>> }
>>>>>> @@ -3417,18 +3461,24 @@ svm_range_trigger_migration(struct
>>>>>> mm_struct *mm, struct svm_range *prange,
>>>>>> *migrated = false;
>>>>>> best_loc = svm_range_best_prefetch_location(prange);
>>>>>> - if (best_loc == KFD_IOCTL_SVM_LOCATION_UNDEFINED ||
>>>>>> - best_loc == prange->actual_loc)
>>>>>> + /* when best_loc is a gpu node and same as prange->actual_loc
>>>>>> + * we still need do migration as prange->actual_loc !=0 does
>>>>>> + * not mean all pages in prange are vram. hmm migrate will pick
>>>>>> + * up right pages during migration.
>>>>>> + */
>>>>>> + if ((best_loc == KFD_IOCTL_SVM_LOCATION_UNDEFINED) ||
>>>>>> + (best_loc == 0 && prange->actual_loc == 0))
>>>>>> return 0;
>>>>>> if (!best_loc) {
>>>>>> - r = svm_migrate_vram_to_ram(prange, mm,
>>>>>> + r = svm_migrate_vram_to_ram(prange, mm, prange->start,
>>>>>> prange->last,
>>>>>> KFD_MIGRATE_TRIGGER_PREFETCH, NULL);
>>>>>> *migrated = !r;
>>>>>> return r;
>>>>>> }
>>>>>> - r = svm_migrate_to_vram(prange, best_loc, mm,
>>>>>> KFD_MIGRATE_TRIGGER_PREFETCH);
>>>>>> + r = svm_migrate_to_vram(prange, best_loc, prange->start,
>>>>>> prange->last,
>>>>>> + mm, KFD_MIGRATE_TRIGGER_PREFETCH);
>>>>>> *migrated = !r;
>>>>>> return r;
>>>>>> @@ -3483,7 +3533,11 @@ static void
>>>>>> svm_range_evict_svm_bo_worker(struct work_struct *work)
>>>>>> mutex_lock(&prange->migrate_mutex);
>>>>>> do {
>>>>>> + /* migrate all vram pages in this prange to sys ram
>>>>>> + * after that prange->actual_loc should be zero
>>>>>> + */
>>>>>> r = svm_migrate_vram_to_ram(prange, mm,
>>>>>> + prange->start, prange->last,
>>>>>> KFD_MIGRATE_TRIGGER_TTM_EVICTION, NULL);
>>>>>> } while (!r && prange->actual_loc && --retries);
>>>>>> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_svm.h
>>>>>> b/drivers/gpu/drm/amd/amdkfd/kfd_svm.h
>>>>>> index 5fd958a97a28..8574cc5eeabd 100644
>>>>>> --- a/drivers/gpu/drm/amd/amdkfd/kfd_svm.h
>>>>>> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_svm.h
>>>>>> @@ -78,6 +78,7 @@ struct svm_work_list_item {
>>>>>> * @update_list:link list node used to add to update_list
>>>>>> * @mapping: bo_va mapping structure to create and update
>>>>>> GPU page table
>>>>>> * @npages: number of pages
>>>>>> + * @vram_pages: vram pages number in this svm_range
>>>>>> * @dma_addr: dma mapping address on each GPU for system
>>>>>> memory physical page
>>>>>> * @ttm_res: vram ttm resource map
>>>>>> * @offset: range start offset within mm_nodes
>>>>>> @@ -88,7 +89,9 @@ struct svm_work_list_item {
>>>>>> * @flags: flags defined as KFD_IOCTL_SVM_FLAG_*
>>>>>> * @perferred_loc: perferred location, 0 for CPU, or GPU id
>>>>>> * @perfetch_loc: last prefetch location, 0 for CPU, or GPU id
>>>>>> - * @actual_loc: the actual location, 0 for CPU, or GPU id
>>>>>> + * @actual_loc: this svm_range location. 0: all pages are from
>>>>>> sys ram;
>>>>>> + * GPU id: this svm_range may include vram pages
>>>>>> from GPU with
>>>>>> + * id actual_loc.
>>>>>> * @granularity:migration granularity, log2 num pages
>>>>>> * @invalid: not 0 means cpu page table is invalidated
>>>>>> * @validate_timestamp: system timestamp when range is validated
>>>>>> @@ -112,6 +115,7 @@ struct svm_range {
>>>>>> struct list_head list;
>>>>>> struct list_head update_list;
>>>>>> uint64_t npages;
>>>>>> + uint64_t vram_pages;
>>>>>> dma_addr_t *dma_addr[MAX_GPU_INSTANCE];
>>>>>> struct ttm_resource *ttm_res;
>>>>>> uint64_t offset;
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