Re: [PATCH 3/3] drm/amdkfd: simplify drain retry fault

[Felix Kuehling]

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?

Regards,
  Felix


Signed-off-by: Philip Yang <philip.y...@amd.com>
---
  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);