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<div class="moz-cite-prefix">On 2021-11-18 11:39 a.m., Felix
Kuehling wrote:<br>
</div>
<blockquote type="cite" cite="mid:423b2831-ba9c-3239-574b-ae3ac8ebb112@amd.com">
<pre class="moz-quote-pre" wrap="">Am 2021-11-18 um 11:19 a.m. schrieb philip yang:
</pre>
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<pre class="moz-quote-pre" wrap="">
On 2021-11-17 7:14 p.m., Felix Kuehling wrote:
</pre>
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<pre class="moz-quote-pre" wrap="">
On 2021-11-16 10:43 p.m., Philip Yang wrote:
</pre>
<blockquote type="cite">
<pre class="moz-quote-pre" wrap="">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.
</pre>
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<pre class="moz-quote-pre" wrap="">Having both svms->drain_pagefaults and svms->draining_faults is
confusing. Do we really need both?
</pre>
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<pre class="moz-quote-pre" wrap="">
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.
</pre>
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<pre class="moz-quote-pre" wrap="">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.
</pre>
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<p>Tanks for the idea to use atomic_cmp_xchg, it will solve the
issue.</p>
<p>Philip<br>
</p>
<blockquote type="cite" cite="mid:423b2831-ba9c-3239-574b-ae3ac8ebb112@amd.com">
<pre class="moz-quote-pre" wrap="">
Regards,
Felix
</pre>
<blockquote type="cite">
<pre class="moz-quote-pre" wrap="">Regards,
Philip
</pre>
<blockquote type="cite">
<pre class="moz-quote-pre" wrap="">Regards,
Felix
</pre>
<blockquote type="cite">
<pre class="moz-quote-pre" wrap="">
Signed-off-by: Philip Yang <a class="moz-txt-link-rfc2396E" href="mailto:Philip.Yang@amd.com"><Philip.Yang@amd.com></a>
---
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);
</pre>
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