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

[Matthew Auld <matthew.auld@xxxxxxxxx>]

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@xxxxxxxxx>
> > > > > >
> > > > > > 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.

> Niranjana
>
> > Niranjana
> >
> > > Niranjana
> > >
> > > > > Niranjana
> > > > >
> > > > > > Reviewed-by: Matthew Auld <matthew.auld@xxxxxxxxx>
> > > > > >
> > > > > > > ---
> > > > > > >  .../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 */