[PATCH v4 2/2] drm/amdgpu: sync page table freeing with tlb flush
Sharma, Shashank
shashank.sharma at amd.com
Fri Mar 1 20:17:26 UTC 2024
On 01/03/2024 14:29, Christian König wrote:
>
>
> Am 01.03.24 um 12:07 schrieb Shashank Sharma:
>> The idea behind this patch is to delay the freeing of PT entry objects
>> until the TLB flush is done.
>>
>> This patch:
>> - Adds a tlb_flush_waitlist which will keep the objects that need to be
>> freed after tlb_flush
>> - Adds PT entries in this list in amdgpu_vm_pt_free_dfs, instead of
>> freeing
>> them immediately.
>> - Exports function amdgpu_vm_pt_free to be called dircetly.
>> - Adds a 'force' input bool to amdgpu_vm_pt_free_dfs to differentiate
>> between immediate freeing of the BOs (like from
>> amdgpu_vm_pt_free_root) vs delayed freeing.
>>
>> V2: rebase
>> V4: (Christian)
>> - add only locked PTEs entries in TLB flush waitlist.
>> - do not create a separate function for list flush.
>> - do not create a new lock for TLB flush.
>> - there is no need to wait on tlb_flush_fence exclusively.
>>
>> Cc: Christian König <Christian.Koenig at amd.com>
>> Cc: Alex Deucher <alexander.deucher at amd.com>
>> Cc: Felix Kuehling <felix.kuehling at amd.com>
>> Cc: Rajneesh Bhardwaj <rajneesh.bhardwaj at amd.com>
>> Signed-off-by: Shashank Sharma <shashank.sharma at amd.com>
>> ---
>> drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c | 10 ++++++++++
>> drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h | 4 ++++
>> drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c | 21 ++++++++++++++-------
>> 3 files changed, 28 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
>> index 310aae6fb49b..94581a1fe34f 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
>> @@ -990,11 +990,20 @@ int amdgpu_vm_update_range(struct amdgpu_device
>> *adev, struct amdgpu_vm *vm,
>> /* Prepare a TLB flush fence to be attached to PTs */
>> if (!unlocked && params.needs_flush && vm->is_compute_context) {
>> + struct amdgpu_vm_bo_base *entry, *next;
>> +
>> amdgpu_vm_tlb_fence_create(adev, vm, fence);
>> /* Makes sure no PD/PT is freed before the flush */
>> dma_resv_add_fence(vm->root.bo->tbo.base.resv, *fence,
>> DMA_RESV_USAGE_BOOKKEEP);
>> +
>> + if (list_empty(&vm->tlb_flush_waitlist))
>> + goto error_unlock;
>> +
>> + /* Now actually free the waitlist */
>> + list_for_each_entry_safe(entry, next,
>> &vm->tlb_flush_waitlist, vm_status)
>> + amdgpu_vm_pt_free(entry);
>
> This needs to be outside of the "if". We also need to free the PDs/PTs
> in non compute VMs.
Noted,
>
>> }
>> error_unlock:
>> @@ -2214,6 +2223,7 @@ int amdgpu_vm_init(struct amdgpu_device *adev,
>> struct amdgpu_vm *vm,
>> INIT_LIST_HEAD(&vm->pt_freed);
>> INIT_WORK(&vm->pt_free_work, amdgpu_vm_pt_free_work);
>> INIT_KFIFO(vm->faults);
>> + INIT_LIST_HEAD(&vm->tlb_flush_waitlist);
>> r = amdgpu_seq64_alloc(adev, &vm->tlb_seq_va,
>> &vm->tlb_seq_cpu_addr);
>> if (r)
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
>> index 298f604b8e5f..ba374c2c61bd 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
>> @@ -343,6 +343,9 @@ struct amdgpu_vm {
>> uint64_t *tlb_seq_cpu_addr;
>> uint64_t tlb_fence_context;
>> + /* temporary storage of PT BOs until the TLB flush */
>> + struct list_head tlb_flush_waitlist;
>> +
>> atomic64_t kfd_last_flushed_seq;
>> /* How many times we had to re-generate the page tables */
>> @@ -545,6 +548,7 @@ int amdgpu_vm_ptes_update(struct
>> amdgpu_vm_update_params *params,
>> uint64_t start, uint64_t end,
>> uint64_t dst, uint64_t flags);
>> void amdgpu_vm_pt_free_work(struct work_struct *work);
>> +void amdgpu_vm_pt_free(struct amdgpu_vm_bo_base *entry);
>> #if defined(CONFIG_DEBUG_FS)
>> void amdgpu_debugfs_vm_bo_info(struct amdgpu_vm *vm, struct
>> seq_file *m);
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c
>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c
>> index 95dc0afdaffb..cb14e5686c0f 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_pt.c
>> @@ -636,7 +636,7 @@ static int amdgpu_vm_pt_alloc(struct
>> amdgpu_device *adev,
>> *
>> * @entry: PDE to free
>> */
>> -static void amdgpu_vm_pt_free(struct amdgpu_vm_bo_base *entry)
>> +void amdgpu_vm_pt_free(struct amdgpu_vm_bo_base *entry)
>> {
>> struct amdgpu_bo *shadow;
>> @@ -685,13 +685,15 @@ void amdgpu_vm_pt_free_work(struct
>> work_struct *work)
>> * @vm: amdgpu vm structure
>> * @start: optional cursor where to start freeing PDs/PTs
>> * @unlocked: vm resv unlock status
>> + * @force: force free all PDs/PTs without waiting for TLB flush
>> *
>> * Free the page directory or page table level and all sub levels.
>> */
>> static void amdgpu_vm_pt_free_dfs(struct amdgpu_device *adev,
>> struct amdgpu_vm *vm,
>> struct amdgpu_vm_pt_cursor *start,
>> - bool unlocked)
>> + bool unlocked,
>> + bool force)
>> {
>> struct amdgpu_vm_pt_cursor cursor;
>> struct amdgpu_vm_bo_base *entry;
>> @@ -708,11 +710,15 @@ static void amdgpu_vm_pt_free_dfs(struct
>> amdgpu_device *adev,
>> return;
>> }
>> - for_each_amdgpu_vm_pt_dfs_safe(adev, vm, start, cursor, entry)
>> - amdgpu_vm_pt_free(entry);
>> + for_each_amdgpu_vm_pt_dfs_safe(adev, vm, start, cursor, entry) {
>> + if (!force)
>> + list_move(&entry->vm_status, &vm->tlb_flush_waitlist);
>> + else
>> + amdgpu_vm_pt_free(entry);
>> + }
>> if (start)
>> - amdgpu_vm_pt_free(start->entry);
>> + list_move(&start->entry->vm_status, &vm->tlb_flush_waitlist);
>> }
>
> The complexity inside amdgpu_vm_pt_free_dfs() really starts to make no
> sense any more.
>
> First of all ditch the usage in amdgpu_vm_pt_free_root(). Instead just
> inline the call to for_each_amdgpu_vm_pt_dfs_safe() to free up all of
> the page tables immediately.
Noted,
>
> Then the other use case in amdgpu_vm_ptes_update():
>
> /* Make sure previous mapping is freed */
> if (cursor.entry->bo) {
> params->table_freed = true;
> amdgpu_vm_pt_free_dfs(adev, params->vm, &cursor, params->unlocked);
> }
>
> We should basically change params->table_freed into a list_head and
> put all to be freed entries on there. Something like that:
>
> spin_lock(&vm->status_lock);
> for_each_amdgpu_vm_pt_dfs_safe(adev, vm, start, cursor, entry)
> list_move(&entry->vm_status, ¶ms->table_freed);
> spin_unlock(&vm->status_lock);
>
> And then finally in amdgpu_vm_update_range() we should call
> amdgpu_vm_pt_free_dfs() to really free up all PDs/PTs (probably rename
> the function while at it).
- in amdgpu_vm_pt_free_dfs, there are two different lists for locked and
unlocked PT entries
unlocked is saved in vm->pt_freed
locked is freed immediately, which we now want to add into another
list (params->table_freed in your suggestion) and free after tlb_flush
which means we have to do something like this:
in amdgpu_vm_ptes_update {
/* Make sure previous mapping is freed */
if (cursor.entry->bo) {
for_each_amdgpu_vm_pt_dfs_safe(adev, vm, start, cursor, entry)
if (unlocked) {
list_move(&entry->vm_status, &vm->pt_free);
else
list_move(&entry->vm_status, ¶ms->table_freed);
}
}
and then we have to change the amdgpu_vm_pt_free_dfs() implementation to
simply free BOs, not searching anything like:
if (unlocked) {
schedule_work(pt_free_work)
} else {
list_for_each(params->table_freed)
amdgpu_vm_pt_free(entry)
}
and then we would be able to call amdgpu_vm_pt_free_dfs() from
amdgpu_vm_update_range().
Does that sound good to you ?
- Shashank
> Regards,
> Christian.
>
>> /**
>> @@ -724,7 +730,7 @@ static void amdgpu_vm_pt_free_dfs(struct
>> amdgpu_device *adev,
>> */
>> void amdgpu_vm_pt_free_root(struct amdgpu_device *adev, struct
>> amdgpu_vm *vm)
>> {
>> - amdgpu_vm_pt_free_dfs(adev, vm, NULL, false);
>> + amdgpu_vm_pt_free_dfs(adev, vm, NULL, false, true);
>> }
>> /**
>> @@ -1059,7 +1065,8 @@ int amdgpu_vm_ptes_update(struct
>> amdgpu_vm_update_params *params,
>> params->needs_flush = true;
>> amdgpu_vm_pt_free_dfs(adev, params->vm,
>> &cursor,
>> - params->unlocked);
>> + params->unlocked,
>> + false);
>> }
>> amdgpu_vm_pt_next(adev, &cursor);
>> }
>
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