[PATCH] drm/amdgpu: check vm bo eviction valuable at last

Christian König christian.koenig at amd.com
Mon Feb 21 08:24:50 UTC 2022


Am 21.02.22 um 04:28 schrieb Qiang Yu:
> On Fri, Feb 18, 2022 at 6:24 PM Christian König
> <ckoenig.leichtzumerken at gmail.com> wrote:
>> Am 18.02.22 um 11:16 schrieb Qiang Yu:
>>> [SNIP]
>>>>> If amdgpu_vm_ready() use evicting flag, it's still not equivalent to check
>>>>> vm idle: true -> vm idle, false -> vm may be idle or busy.
>>>> Yeah, but why should that be relevant?
>>>>
>>>> The amdgpu_vm_ready() return if we can do page table updates or not. If
>>>> the VM is idle or not is only relevant for eviction.
>>>>
>>>> In other words any CS or page table update makes the VM busy, but that
>>>> only affects if the VM can be evicted or not.
>>>>
>>> My point is: we can't use amdgpu_vm_ready() to replace vm_is_busy(), so
>>> currently we update vm even when vm is busy. So why not use:
> Sorry, should be "vm is idle".
>
>>> if (!amdgpu_vm_ready() || vm_is_busy()) return;
>>> in amdgpu_gem_va_update_vm(), as you mentioned we prefer to not
>>> update vm when it's idle.
>> Because updating the VM while it is busy is perfectly fine, we do it all
>> the time.
>>
> Yeah, as above, my typo.
>
>> We should just not update it when it is already idle and was considered
>> for eviction.
> "and", not "or"?
>
>> In this situation it makes most of the time sense to keep
>> it idle and postpone the update till the next command submission.
>>
>>>>>>> Then we can keep the evicting flag accurate (after solving your
>>>>>>> concern for this patch that eviction may fail latter by further delay
>>>>>>> the flag update after eviction success).
>>>>>> That won't work. See we need to mark the VM as evicted before we
>>>>>> actually evict them because otherwise somebody could use the VM in
>>>>>> parallel and add another fence to it.
>>>>>>
>>>>> I see, make this too accurate should cost too much like holding the
>>>>> eviction_lock when eviction. But just delay it in
>>>>> amdgpu_ttm_bo_eviction_valuable()
>>>>> could avoid most false positive case.
>>>> Partially correct. Another fundamental problem is that we can't hold the
>>>> eviction lock because that would result in lock inversion and potential
>>>> deadlock.
>>>>
>>>> We could set the flag later on, but as I said before that when we set
>>>> the evicted flag when the VM is already idle is a desired effect.
>>>>
>>> As above, this confuse me as we can explicitly check vm idle when
>>> user update vm, why bother to embed it in evicting flag implicitly?
>> Well as I said it's irrelevant for the update if the VM is idle or not.
>>
>> To summarize the rules once more:
>> 1. When VM page tables are used by CS or page tables updates it is
>> considered busy, e.g. not idle.
>>
>> 2. When we want to evict a VM it must be idle. As soon as we considered
>> this we should set the evicted flag to make sure to keep it idle as much
>> as possible.
>>
>> 3. When we want to update the page tables we just need to check if the
>> VM is idle or not.
>>
> But now we does not check vm idle directly in amdgpu_gem_va_update_vm().
> If VM bo has not been considered for eviction, it could be either idle or busy.
>
> Just want to confirm if the fix should be only change amdgpu_vm_ready()
> to use evicting flag or besides using evicting flag, also check vm_idle() in
> amdgpu_gem_va_update_vm().

Only changing the amdgpu_vm_ready() should be enough. It can be that 
this then bubbles up more issue, but those need to be taken care of 
separately then.

Regards,
Christian.

>
> Regards,
> Qiang
>
>> 4. When a CS happens we don't have another chance and make the VM busy
>> again. And do all postponed page table updates.
>>
> Anyway,
>
>> Regards,
>> Christian.
>>
>>> Check vm idle need to hold resv lock. Read your patch for adding
>>> evicting flag is to update vm without resv lock. But user vm ops in
>>> amdgpu_gem_va_update_vm() do hold the resv lock, so the difference
>>> happens when calling amdgpu_vm_bo_update_mapping() from
>>> svm_range_(un)map_to_gpu(). So embed vm idle in evicting flag
>>> is for svm_range_(un)map_to_gpu() also do nothing when vm idle?
>>
>>
>>> Regards,
>>> Qiang
>>>
>>>> Regards,
>>>> Christian.
>>>>
>>>>> Regards,
>>>>> Qiang
>>>>>
>>>>>> Regards,
>>>>>> Christian.
>>>>>>
>>>>>>> Regards,
>>>>>>> Qiang
>>>>>>>
>>>>>>>
>>>>>>>> Regards,
>>>>>>>> Christian.
>>>>>>>>
>>>>>>>>> Regards,
>>>>>>>>> Qiang
>>>>>>>>>
>>>>>>>>>> Regards,
>>>>>>>>>> Christian.
>>>>>>>>>>
>>>>>>>>>>> Regards,
>>>>>>>>>>> Qiang
>>>>>>>>>>>
>>>>>>>>>>>> Regards,
>>>>>>>>>>>> Christian.
>>>>>>>>>>>>
>>>>>>>>>>>>> Regards,
>>>>>>>>>>>>> Qiang
>>>>>>>>>>>>>
>>>>>>>>>>>>>> What we should rather do is to fix amdgpu_vm_ready() to take a look at
>>>>>>>>>>>>>> the flag instead of the linked list.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> Regards,
>>>>>>>>>>>>>> Christian.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> Signed-off-by: Qiang Yu <qiang.yu at amd.com>
>>>>>>>>>>>>>>> ---
>>>>>>>>>>>>>>>          drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 85 ++++++++++++++-----------
>>>>>>>>>>>>>>>          1 file changed, 47 insertions(+), 38 deletions(-)
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
>>>>>>>>>>>>>>> index 5a32ee66d8c8..88a27911054f 100644
>>>>>>>>>>>>>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
>>>>>>>>>>>>>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
>>>>>>>>>>>>>>> @@ -1306,45 +1306,11 @@ uint64_t amdgpu_ttm_tt_pte_flags(struct amdgpu_device *adev, struct ttm_tt *ttm,
>>>>>>>>>>>>>>>              return flags;
>>>>>>>>>>>>>>>          }
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> -/*
>>>>>>>>>>>>>>> - * amdgpu_ttm_bo_eviction_valuable - Check to see if we can evict a buffer
>>>>>>>>>>>>>>> - * object.
>>>>>>>>>>>>>>> - *
>>>>>>>>>>>>>>> - * Return true if eviction is sensible. Called by ttm_mem_evict_first() on
>>>>>>>>>>>>>>> - * behalf of ttm_bo_mem_force_space() which tries to evict buffer objects until
>>>>>>>>>>>>>>> - * it can find space for a new object and by ttm_bo_force_list_clean() which is
>>>>>>>>>>>>>>> - * used to clean out a memory space.
>>>>>>>>>>>>>>> - */
>>>>>>>>>>>>>>> -static bool amdgpu_ttm_bo_eviction_valuable(struct ttm_buffer_object *bo,
>>>>>>>>>>>>>>> -                                         const struct ttm_place *place)
>>>>>>>>>>>>>>> +static bool amdgpu_ttm_mem_eviction_valuable(struct ttm_buffer_object *bo,
>>>>>>>>>>>>>>> +                                          const struct ttm_place *place)
>>>>>>>>>>>>>>>          {
>>>>>>>>>>>>>>>              unsigned long num_pages = bo->resource->num_pages;
>>>>>>>>>>>>>>>              struct amdgpu_res_cursor cursor;
>>>>>>>>>>>>>>> -     struct dma_resv_list *flist;
>>>>>>>>>>>>>>> -     struct dma_fence *f;
>>>>>>>>>>>>>>> -     int i;
>>>>>>>>>>>>>>> -
>>>>>>>>>>>>>>> -     /* Swapout? */
>>>>>>>>>>>>>>> -     if (bo->resource->mem_type == TTM_PL_SYSTEM)
>>>>>>>>>>>>>>> -             return true;
>>>>>>>>>>>>>>> -
>>>>>>>>>>>>>>> -     if (bo->type == ttm_bo_type_kernel &&
>>>>>>>>>>>>>>> -         !amdgpu_vm_evictable(ttm_to_amdgpu_bo(bo)))
>>>>>>>>>>>>>>> -             return false;
>>>>>>>>>>>>>>> -
>>>>>>>>>>>>>>> -     /* If bo is a KFD BO, check if the bo belongs to the current process.
>>>>>>>>>>>>>>> -      * If true, then return false as any KFD process needs all its BOs to
>>>>>>>>>>>>>>> -      * be resident to run successfully
>>>>>>>>>>>>>>> -      */
>>>>>>>>>>>>>>> -     flist = dma_resv_shared_list(bo->base.resv);
>>>>>>>>>>>>>>> -     if (flist) {
>>>>>>>>>>>>>>> -             for (i = 0; i < flist->shared_count; ++i) {
>>>>>>>>>>>>>>> -                     f = rcu_dereference_protected(flist->shared[i],
>>>>>>>>>>>>>>> -                             dma_resv_held(bo->base.resv));
>>>>>>>>>>>>>>> -                     if (amdkfd_fence_check_mm(f, current->mm))
>>>>>>>>>>>>>>> -                             return false;
>>>>>>>>>>>>>>> -             }
>>>>>>>>>>>>>>> -     }
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>              switch (bo->resource->mem_type) {
>>>>>>>>>>>>>>>              case AMDGPU_PL_PREEMPT:
>>>>>>>>>>>>>>> @@ -1377,10 +1343,53 @@ static bool amdgpu_ttm_bo_eviction_valuable(struct ttm_buffer_object *bo,
>>>>>>>>>>>>>>>                      return false;
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>              default:
>>>>>>>>>>>>>>> -             break;
>>>>>>>>>>>>>>> +             return ttm_bo_eviction_valuable(bo, place);
>>>>>>>>>>>>>>>              }
>>>>>>>>>>>>>>> +}
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> -     return ttm_bo_eviction_valuable(bo, place);
>>>>>>>>>>>>>>> +/*
>>>>>>>>>>>>>>> + * amdgpu_ttm_bo_eviction_valuable - Check to see if we can evict a buffer
>>>>>>>>>>>>>>> + * object.
>>>>>>>>>>>>>>> + *
>>>>>>>>>>>>>>> + * Return true if eviction is sensible. Called by ttm_mem_evict_first() on
>>>>>>>>>>>>>>> + * behalf of ttm_bo_mem_force_space() which tries to evict buffer objects until
>>>>>>>>>>>>>>> + * it can find space for a new object and by ttm_bo_force_list_clean() which is
>>>>>>>>>>>>>>> + * used to clean out a memory space.
>>>>>>>>>>>>>>> + */
>>>>>>>>>>>>>>> +static bool amdgpu_ttm_bo_eviction_valuable(struct ttm_buffer_object *bo,
>>>>>>>>>>>>>>> +                                         const struct ttm_place *place)
>>>>>>>>>>>>>>> +{
>>>>>>>>>>>>>>> +     struct dma_resv_list *flist;
>>>>>>>>>>>>>>> +     struct dma_fence *f;
>>>>>>>>>>>>>>> +     int i;
>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>> +     /* Swapout? */
>>>>>>>>>>>>>>> +     if (bo->resource->mem_type == TTM_PL_SYSTEM)
>>>>>>>>>>>>>>> +             return true;
>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>> +     /* If bo is a KFD BO, check if the bo belongs to the current process.
>>>>>>>>>>>>>>> +      * If true, then return false as any KFD process needs all its BOs to
>>>>>>>>>>>>>>> +      * be resident to run successfully
>>>>>>>>>>>>>>> +      */
>>>>>>>>>>>>>>> +     flist = dma_resv_shared_list(bo->base.resv);
>>>>>>>>>>>>>>> +     if (flist) {
>>>>>>>>>>>>>>> +             for (i = 0; i < flist->shared_count; ++i) {
>>>>>>>>>>>>>>> +                     f = rcu_dereference_protected(flist->shared[i],
>>>>>>>>>>>>>>> +                             dma_resv_held(bo->base.resv));
>>>>>>>>>>>>>>> +                     if (amdkfd_fence_check_mm(f, current->mm))
>>>>>>>>>>>>>>> +                             return false;
>>>>>>>>>>>>>>> +             }
>>>>>>>>>>>>>>> +     }
>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>> +     /* Check by different mem type. */
>>>>>>>>>>>>>>> +     if (!amdgpu_ttm_mem_eviction_valuable(bo, place))
>>>>>>>>>>>>>>> +             return false;
>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>> +     /* VM bo should be checked at last because it will mark VM evicting. */
>>>>>>>>>>>>>>> +     if (bo->type == ttm_bo_type_kernel)
>>>>>>>>>>>>>>> +             return amdgpu_vm_evictable(ttm_to_amdgpu_bo(bo));
>>>>>>>>>>>>>>> +
>>>>>>>>>>>>>>> +     return true;
>>>>>>>>>>>>>>>          }
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>          static void amdgpu_ttm_vram_mm_access(struct amdgpu_device *adev, loff_t pos,



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