Re: [Intel-gfx] [PATCH v7 20/20] drm/i915/vm_bind: Async vm_unbind support

[Matthew Auld <matthew.auld@intel.com>]

On 29/11/2022 23:26, Niranjana Vishwanathapura wrote:
> On Wed, Nov 23, 2022 at 11:42:58AM +0000, Matthew Auld wrote:
>> On 16/11/2022 00:37, Niranjana Vishwanathapura wrote:
>>> On Tue, Nov 15, 2022 at 03:15:03PM -0800, Niranjana Vishwanathapura 
>>> wrote:
>>>> On Tue, Nov 15, 2022 at 08:33:47AM -0800, Niranjana Vishwanathapura 
>>>> wrote:
>>>>> On Tue, Nov 15, 2022 at 04:20:54PM +0000, Matthew Auld wrote:
>>>>>> On 15/11/2022 16:15, Niranjana Vishwanathapura wrote:
>>>>>>> On Tue, Nov 15, 2022 at 11:05:21AM +0000, Matthew Auld wrote:
>>>>>>>> On 13/11/2022 07:57, Niranjana Vishwanathapura wrote:
>>>>>>>>> Asynchronously unbind the vma upon vm_unbind call.
>>>>>>>>> Fall back to synchronous unbind if backend doesn't support
>>>>>>>>> async unbind or if async unbind fails.
>>>>>>>>>
>>>>>>>>> No need for vm_unbind out fence support as i915 will internally
>>>>>>>>> handle all sequencing and user need not try to sequence any
>>>>>>>>> operation with the unbind completion.
>>>>>>>>>
>>>>>>>>> v2: use i915_vma_destroy_async in vm_unbind ioctl
>>>>>>>>>
>>>>>>>>> Signed-off-by: Niranjana Vishwanathapura 
>>>>>>>>> <niranjana.vishwanathapura@intel.com>
>>>>>>>>
>>>>>>>> This only does it for non-partial vma, right? Or was that 
>>>>>>>> changed somewhere?
>>>>>>>>
>>>>>>>
>>>>>>> No, it applies to any vma (partial or non-partial).
>>>>>>> It was so from the beginning.
>>>>>>
>>>>>> Doesn't __i915_vma_unbind_async() return an error when mm.pages != 
>>>>>> vma->pages? IIRC this was discussed before. Just trying to think 
>>>>>> about the consequences of this change.
>>>>>
>>>>> I am not seeing any such restriction. Let me probe and check if there
>>>>> is any such restriction anywhere in the call chain.
>>>>
>>>> I checked and I am not seeing any restriction anywher in the call 
>>>> chain.
>>>>
>>>
>>> Note that just like binding case, unbinding is also synchronous unless
>>> there is a pending activity, in which case, it will be asynchronous.
>>
>> In __i915_vma_unbind_async() there is:
>>
>> if (i915_vma_is_pinned(vma) ||
>>    &vma->obj->mm.rsgt->table != vma->resource->bi.pages)
>>        return ERR_PTR(-EAGAIN);
>>
>> AFAICT we then also don't get any pipelined moves with such an object, 
>> if there is such a binding present.
> 
> I had to remove this check as otherwise for VM_BIND (persistent) mappings,
> it will alwasy be true and we will always endup with -EAGAIN.
> Persistent mappings, as they support partial binding, can't have an sg
> table which is just a pointer to object's sg table.

Ok, maybe make that a seperate patch, since it seems to change the 
behaviour for more than just persisent mappings, AFAICT.

> 
> Niranjana
> 
>>
>>>
>>> Niranjana
>>>
>>>> Niranjana
>>>>
>>>>>
>>>>> Niranjana
>>>>>
>>>>>>
>>>>>>>
>>>>>>> Niranjana
>>>>>>>
>>>>>>>> Reviewed-by: Matthew Auld <matthew.auld@intel.com>
>>>>>>>>
>>>>>>>>> ---
>>>>>>>>>  .../drm/i915/gem/i915_gem_vm_bind_object.c    |  2 +-
>>>>>>>>>  drivers/gpu/drm/i915/i915_vma.c               | 51 
>>>>>>>>> +++++++++++++++++--
>>>>>>>>>  drivers/gpu/drm/i915/i915_vma.h               |  1 +
>>>>>>>>>  include/uapi/drm/i915_drm.h                   |  3 +-
>>>>>>>>>  4 files changed, 51 insertions(+), 6 deletions(-)
>>>>>>>>>
>>>>>>>>> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_vm_bind_object.c 
>>>>>>>>> b/drivers/gpu/drm/i915/gem/i915_gem_vm_bind_object.c
>>>>>>>>> index d87d1210365b..36651b447966 100644
>>>>>>>>> --- a/drivers/gpu/drm/i915/gem/i915_gem_vm_bind_object.c
>>>>>>>>> +++ b/drivers/gpu/drm/i915/gem/i915_gem_vm_bind_object.c
>>>>>>>>> @@ -210,7 +210,7 @@ static int i915_gem_vm_unbind_vma(struct 
>>>>>>>>> i915_address_space *vm,
>>>>>>>>>       */
>>>>>>>>>      obj = vma->obj;
>>>>>>>>>      i915_gem_object_lock(obj, NULL);
>>>>>>>>> -    i915_vma_destroy(vma);
>>>>>>>>> +    i915_vma_destroy_async(vma);
>>>>>>>>>      i915_gem_object_unlock(obj);
>>>>>>>>>      i915_gem_object_put(obj);
>>>>>>>>> diff --git a/drivers/gpu/drm/i915/i915_vma.c 
>>>>>>>>> b/drivers/gpu/drm/i915/i915_vma.c
>>>>>>>>> index 7cf77c67d755..483d25f2425c 100644
>>>>>>>>> --- a/drivers/gpu/drm/i915/i915_vma.c
>>>>>>>>> +++ b/drivers/gpu/drm/i915/i915_vma.c
>>>>>>>>> @@ -42,6 +42,8 @@
>>>>>>>>>  #include "i915_vma.h"
>>>>>>>>>  #include "i915_vma_resource.h"
>>>>>>>>> +static struct dma_fence *__i915_vma_unbind_async(struct 
>>>>>>>>> i915_vma *vma);
>>>>>>>>> +
>>>>>>>>>  static inline void assert_vma_held_evict(const struct i915_vma 
>>>>>>>>> *vma)
>>>>>>>>>  {
>>>>>>>>>      /*
>>>>>>>>> @@ -1713,7 +1715,7 @@ void i915_vma_reopen(struct i915_vma *vma)
>>>>>>>>>      spin_unlock_irq(&gt->closed_lock);
>>>>>>>>>  }
>>>>>>>>> -static void force_unbind(struct i915_vma *vma)
>>>>>>>>> +static void force_unbind(struct i915_vma *vma, bool async)
>>>>>>>>>  {
>>>>>>>>>      if (!drm_mm_node_allocated(&vma->node))
>>>>>>>>>          return;
>>>>>>>>> @@ -1727,7 +1729,21 @@ static void force_unbind(struct i915_vma 
>>>>>>>>> *vma)
>>>>>>>>>          i915_vma_set_purged(vma);
>>>>>>>>>      atomic_and(~I915_VMA_PIN_MASK, &vma->flags);
>>>>>>>>> -    WARN_ON(__i915_vma_unbind(vma));
>>>>>>>>> +    if (async) {
>>>>>>>>> +        struct dma_fence *fence;
>>>>>>>>> +
>>>>>>>>> +        fence = __i915_vma_unbind_async(vma);
>>>>>>>>> +        if (IS_ERR_OR_NULL(fence)) {
>>>>>>>>> +            async = false;
>>>>>>>>> +        } else {
>>>>>>>>> +            dma_resv_add_fence(vma->obj->base.resv, fence,
>>>>>>>>> +                       DMA_RESV_USAGE_READ);
>>>>>>>>> +            dma_fence_put(fence);
>>>>>>>>> +        }
>>>>>>>>> +    }
>>>>>>>>> +
>>>>>>>>> +    if (!async)
>>>>>>>>> +        WARN_ON(__i915_vma_unbind(vma));
>>>>>>>>>      GEM_BUG_ON(drm_mm_node_allocated(&vma->node));
>>>>>>>>>  }
>>>>>>>>> @@ -1787,7 +1803,7 @@ void i915_vma_destroy_locked(struct 
>>>>>>>>> i915_vma *vma)
>>>>>>>>>  {
>>>>>>>>>      lockdep_assert_held(&vma->vm->mutex);
>>>>>>>>> -    force_unbind(vma);
>>>>>>>>> +    force_unbind(vma, false);
>>>>>>>>>      list_del_init(&vma->vm_link);
>>>>>>>>>      release_references(vma, vma->vm->gt, false);
>>>>>>>>>  }
>>>>>>>>> @@ -1798,7 +1814,34 @@ void i915_vma_destroy(struct i915_vma *vma)
>>>>>>>>>      bool vm_ddestroy;
>>>>>>>>>      mutex_lock(&vma->vm->mutex);
>>>>>>>>> -    force_unbind(vma);
>>>>>>>>> +    force_unbind(vma, false);
>>>>>>>>> +    list_del_init(&vma->vm_link);
>>>>>>>>> +    vm_ddestroy = vma->vm_ddestroy;
>>>>>>>>> +    vma->vm_ddestroy = false;
>>>>>>>>> +
>>>>>>>>> +    /* vma->vm may be freed when releasing vma->vm->mutex. */
>>>>>>>>> +    gt = vma->vm->gt;
>>>>>>>>> +    mutex_unlock(&vma->vm->mutex);
>>>>>>>>> +    release_references(vma, gt, vm_ddestroy);
>>>>>>>>> +}
>>>>>>>>> +
>>>>>>>>> +void i915_vma_destroy_async(struct i915_vma *vma)
>>>>>>>>> +{
>>>>>>>>> +    bool vm_ddestroy, async = vma->obj->mm.rsgt;
>>>>>>>>> +    struct intel_gt *gt;
>>>>>>>>> +
>>>>>>>>> +    if (dma_resv_reserve_fences(vma->obj->base.resv, 1))
>>>>>>>>> +        async = false;
>>>>>>>>> +
>>>>>>>>> +    mutex_lock(&vma->vm->mutex);
>>>>>>>>> +    /*
>>>>>>>>> +     * Ensure any asynchronous binding is complete while using
>>>>>>>>> +     * async unbind as we will be releasing the vma here.
>>>>>>>>> +     */
>>>>>>>>> +    if (async && i915_active_wait(&vma->active))
>>>>>>>>> +        async = false;
>>>>>>>>> +
>>>>>>>>> +    force_unbind(vma, async);
>>>>>>>>>      list_del_init(&vma->vm_link);
>>>>>>>>>      vm_ddestroy = vma->vm_ddestroy;
>>>>>>>>>      vma->vm_ddestroy = false;
>>>>>>>>> diff --git a/drivers/gpu/drm/i915/i915_vma.h 
>>>>>>>>> b/drivers/gpu/drm/i915/i915_vma.h
>>>>>>>>> index 737ef310d046..25f15965dab8 100644
>>>>>>>>> --- a/drivers/gpu/drm/i915/i915_vma.h
>>>>>>>>> +++ b/drivers/gpu/drm/i915/i915_vma.h
>>>>>>>>> @@ -272,6 +272,7 @@ void i915_vma_reopen(struct i915_vma *vma);
>>>>>>>>>  void i915_vma_destroy_locked(struct i915_vma *vma);
>>>>>>>>>  void i915_vma_destroy(struct i915_vma *vma);
>>>>>>>>> +void i915_vma_destroy_async(struct i915_vma *vma);
>>>>>>>>>  #define assert_vma_held(vma) 
>>>>>>>>> dma_resv_assert_held((vma)->obj->base.resv)
>>>>>>>>> diff --git a/include/uapi/drm/i915_drm.h 
>>>>>>>>> b/include/uapi/drm/i915_drm.h
>>>>>>>>> index e5600f358a15..431d40bb1dee 100644
>>>>>>>>> --- a/include/uapi/drm/i915_drm.h
>>>>>>>>> +++ b/include/uapi/drm/i915_drm.h
>>>>>>>>> @@ -3969,7 +3969,8 @@ struct drm_i915_gem_vm_bind {
>>>>>>>>>   * any error.
>>>>>>>>>   *
>>>>>>>>>   * VM_BIND/UNBIND ioctl calls executed on different CPU 
>>>>>>>>> threads concurrently
>>>>>>>>> - * are not ordered.
>>>>>>>>> + * are not ordered. Furthermore, parts of the VM_UNBIND 
>>>>>>>>> operation can be done
>>>>>>>>> + * asynchronously.
>>>>>>>>>   */
>>>>>>>>>  struct drm_i915_gem_vm_unbind {
>>>>>>>>>      /** @vm_id: VM (address space) id to bind */