Am 2021-11-18 um 11:19 a.m. schrieb philip yang:
>
>
> On 2021-11-17 7:14 p.m., Felix Kuehling wrote:
>>
>> On 2021-11-16 10:43 p.m., Philip Yang wrote:
>>> unmap range always set svms->drain_pagefaults flag to simplify both
>>> parent range and child range unmap. Deferred list work takes mmap write
>>> lock to read and clear svms->drain_pagefaults, to serialize with unmap
>>> callback.
>>>
>>> Add atomic flag svms->draining_faults, if svms->draining_faults is set,
>>> page fault handle ignore the retry fault, to speed up interrupt
>>> handling.
>> Having both svms->drain_pagefaults and svms->draining_faults is
>> confusing. Do we really need both?
>
> Using one flag, I can not find a way to handle the case, unmap new
> range. if the flag is set, restore_pages uses the flag to drop fault,
> then drain_retry_fault reset the flag after draining is done, we will
> not able to drain retry fault for the new range.
>
I think the correct solution would be to use atomic_inc to set the flag
and atomic_cmp_xchg in svm_range_drain_retry_fault to clear it. If the
flag was changed while svm_range_drain_retry_fault executed, it means
another drain was requested by someone else and the flag should remain
set for another round of draining.
Regards,
Felix
> Regards,
>
> Philip
>
>> Regards,
>> Felix
>>
>>>
>>> Signed-off-by: Philip Yang <Philip.Yang@xxxxxxx>
>>> ---
>>> drivers/gpu/drm/amd/amdkfd/kfd_priv.h | 1 +
>>> drivers/gpu/drm/amd/amdkfd/kfd_svm.c | 24 ++++++++++++++++++------
>>> 2 files changed, 19 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_priv.h
>>> b/drivers/gpu/drm/amd/amdkfd/kfd_priv.h
>>> index 1d3f012bcd2a..4e4640b731e1 100644
>>> --- a/drivers/gpu/drm/amd/amdkfd/kfd_priv.h
>>> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_priv.h
>>> @@ -767,6 +767,7 @@ struct svm_range_list {
>>> spinlock_t deferred_list_lock;
>>> atomic_t evicted_ranges;
>>> bool drain_pagefaults;
>>> + atomic_t draining_faults;
>>> struct delayed_work restore_work;
>>> DECLARE_BITMAP(bitmap_supported, MAX_GPU_INSTANCE);
>>> struct task_struct *faulting_task;
>>> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
>>> b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
>>> index 3eb0a9491755..d332462bf9d3 100644
>>> --- a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
>>> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
>>> @@ -1962,6 +1962,7 @@ void svm_range_drain_retry_fault(struct
>>> svm_range_list *svms)
>>> p = container_of(svms, struct kfd_process, svms);
>>> + atomic_set(&svms->draining_faults, 1);
>>> for_each_set_bit(i, svms->bitmap_supported, p->n_pdds) {
>>> pdd = p->pdds[i];
>>> if (!pdd)
>>> @@ -1975,6 +1976,7 @@ void svm_range_drain_retry_fault(struct
>>> svm_range_list *svms)
>>> flush_work(&adev->irq.ih1_work);
>>> pr_debug("drain retry fault gpu %d svms 0x%p done\n", i,
>>> svms);
>>> }
>>> + atomic_set(&svms->draining_faults, 0);
>>> }
>>> static void svm_range_deferred_list_work(struct work_struct *work)
>>> @@ -2002,6 +2004,7 @@ static void
>>> svm_range_deferred_list_work(struct work_struct *work)
>>> * mmap write lock to serialize with munmap notifiers.
>>> */
>>> if (unlikely(READ_ONCE(svms->drain_pagefaults))) {
>>> + atomic_set(&svms->draining_faults, 1);
>>> WRITE_ONCE(svms->drain_pagefaults, false);
>>> mmap_write_unlock(mm);
>>> svm_range_drain_retry_fault(svms);
>>> @@ -2049,12 +2052,6 @@ svm_range_add_list_work(struct svm_range_list
>>> *svms, struct svm_range *prange,
>>> struct mm_struct *mm, enum svm_work_list_ops op)
>>> {
>>> spin_lock(&svms->deferred_list_lock);
>>> - /* Make sure pending page faults are drained in the deferred
>>> worker
>>> - * before the range is freed to avoid straggler interrupts on
>>> - * unmapped memory causing "phantom faults".
>>> - */
>>> - if (op == SVM_OP_UNMAP_RANGE)
>>> - svms->drain_pagefaults = true;
>>> /* if prange is on the deferred list */
>>> if (!list_empty(&prange->deferred_list)) {
>>> pr_debug("update exist prange 0x%p work op %d\n", prange,
>>> op);
>>> @@ -2133,6 +2130,13 @@ svm_range_unmap_from_cpu(struct mm_struct
>>> *mm, struct svm_range *prange,
>>> pr_debug("svms 0x%p prange 0x%p [0x%lx 0x%lx] [0x%lx
>>> 0x%lx]\n", svms,
>>> prange, prange->start, prange->last, start, last);
>>> + /* Make sure pending page faults are drained in the deferred
>>> worker
>>> + * before the range is freed to avoid straggler interrupts on
>>> + * unmapped memory causing "phantom faults".
>>> + */
>>> + pr_debug("set range drain_pagefaults true\n");
>>> + WRITE_ONCE(svms->drain_pagefaults, true);
>>> +
>>> unmap_parent = start <= prange->start && last >= prange->last;
>>> list_for_each_entry(pchild, &prange->child_list, child_list) {
>>> @@ -2595,6 +2599,13 @@ svm_range_restore_pages(struct amdgpu_device
>>> *adev, unsigned int pasid,
>>> mm = p->mm;
>>> mmap_write_lock(mm);
>>> + if (!!atomic_read(&svms->draining_faults) ||
>>> + READ_ONCE(svms->drain_pagefaults)) {
>>> + pr_debug("draining retry fault, drop fault 0x%llx\n", addr);
>>> + mmap_write_downgrade(mm);
>>> + goto out_unlock_mm;
>>> + }
>>> +
>>> vma = find_vma(p->mm, addr << PAGE_SHIFT);
>>> if (!vma || (addr << PAGE_SHIFT) < vma->vm_start) {
>>> pr_debug("VMA not found for address 0x%llx\n", addr);
>>> @@ -2732,6 +2743,7 @@ int svm_range_list_init(struct kfd_process *p)
>>> mutex_init(&svms->lock);
>>> INIT_LIST_HEAD(&svms->list);
>>> atomic_set(&svms->evicted_ranges, 0);
>>> + atomic_set(&svms->draining_faults, 0);
>>> INIT_DELAYED_WORK(&svms->restore_work, svm_range_restore_work);
>>> INIT_WORK(&svms->deferred_list_work,
>>> svm_range_deferred_list_work);
>>> INIT_LIST_HEAD(&svms->deferred_range_list);
