Re: [PATCH drm-misc-next v9 06/11] drm/nouveau: fence: separate fence alloc and emit

[Danilo Krummrich <dakr@xxxxxxxxxx>]

Hi Christian,

On 8/7/23 20:07, Christian König wrote:
> Am 03.08.23 um 18:52 schrieb Danilo Krummrich:
> > The new (VM_BIND) UAPI exports DMA fences through DRM syncobjs. Hence,
> > in order to emit fences within DMA fence signalling critical sections
> > (e.g. as typically done in the DRM GPU schedulers run_job() callback) we
> > need to separate fence allocation and fence emitting.
>
> At least from the description that sounds like it might be illegal. 
> Daniel can you take a look as well.
>
> What exactly are you doing here?

I'm basically doing exactly the same as amdgpu_fence_emit() does in 
amdgpu_ib_schedule() called by amdgpu_job_run().

The difference - and this is what this patch is for - is that I separate 
the fence allocation from emitting the fence, such that the fence 
structure is allocated before the job is submitted to the GPU scheduler. 
amdgpu solves this with GFP_ATOMIC within amdgpu_fence_emit() to 
allocate the fence structure in this case.

- Danilo

> Regards,
> Christian.
>
> > Signed-off-by: Danilo Krummrich <dakr@xxxxxxxxxx>
> > ---
> >   drivers/gpu/drm/nouveau/dispnv04/crtc.c |  9 ++++-
> >   drivers/gpu/drm/nouveau/nouveau_bo.c    | 52 +++++++++++++++----------
> >   drivers/gpu/drm/nouveau/nouveau_chan.c  |  6 ++-
> >   drivers/gpu/drm/nouveau/nouveau_dmem.c  |  9 +++--
> >   drivers/gpu/drm/nouveau/nouveau_fence.c | 16 +++-----
> >   drivers/gpu/drm/nouveau/nouveau_fence.h |  3 +-
> >   drivers/gpu/drm/nouveau/nouveau_gem.c   |  5 ++-
> >   7 files changed, 59 insertions(+), 41 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/nouveau/dispnv04/crtc.c 
> > b/drivers/gpu/drm/nouveau/dispnv04/crtc.c
> > index a6f2e681bde9..a34924523133 100644
> > --- a/drivers/gpu/drm/nouveau/dispnv04/crtc.c
> > +++ b/drivers/gpu/drm/nouveau/dispnv04/crtc.c
> > @@ -1122,11 +1122,18 @@ nv04_page_flip_emit(struct nouveau_channel *chan,
> >       PUSH_NVSQ(push, NV_SW, NV_SW_PAGE_FLIP, 0x00000000);
> >       PUSH_KICK(push);
> > -    ret = nouveau_fence_new(chan, false, pfence);
> > +    ret = nouveau_fence_new(pfence);
> >       if (ret)
> >           goto fail;
> > +    ret = nouveau_fence_emit(*pfence, chan);
> > +    if (ret)
> > +        goto fail_fence_unref;
> > +
> >       return 0;
> > +
> > +fail_fence_unref:
> > +    nouveau_fence_unref(pfence);
> >   fail:
> >       spin_lock_irqsave(&dev->event_lock, flags);
> >       list_del(&s->head);
> > diff --git a/drivers/gpu/drm/nouveau/nouveau_bo.c 
> > b/drivers/gpu/drm/nouveau/nouveau_bo.c
> > index 057bc995f19b..e9cbbf594e6f 100644
> > --- a/drivers/gpu/drm/nouveau/nouveau_bo.c
> > +++ b/drivers/gpu/drm/nouveau/nouveau_bo.c
> > @@ -820,29 +820,39 @@ nouveau_bo_move_m2mf(struct ttm_buffer_object 
> > *bo, int evict,
> >           mutex_lock(&cli->mutex);
> >       else
> >           mutex_lock_nested(&cli->mutex, SINGLE_DEPTH_NESTING);
> > +
> >       ret = nouveau_fence_sync(nouveau_bo(bo), chan, true, 
> > ctx->interruptible);
> > -    if (ret == 0) {
> > -        ret = drm->ttm.move(chan, bo, bo->resource, new_reg);
> > -        if (ret == 0) {
> > -            ret = nouveau_fence_new(chan, false, &fence);
> > -            if (ret == 0) {
> > -                /* TODO: figure out a better solution here
> > -                 *
> > -                 * wait on the fence here explicitly as going through
> > -                 * ttm_bo_move_accel_cleanup somehow doesn't seem to 
> > do it.
> > -                 *
> > -                 * Without this the operation can timeout and we'll 
> > fallback to a
> > -                 * software copy, which might take several minutes to 
> > finish.
> > -                 */
> > -                nouveau_fence_wait(fence, false, false);
> > -                ret = ttm_bo_move_accel_cleanup(bo,
> > -                                &fence->base,
> > -                                evict, false,
> > -                                new_reg);
> > -                nouveau_fence_unref(&fence);
> > -            }
> > -        }
> > +    if (ret)
> > +        goto out_unlock;
> > +
> > +    ret = drm->ttm.move(chan, bo, bo->resource, new_reg);
> > +    if (ret)
> > +        goto out_unlock;
> > +
> > +    ret = nouveau_fence_new(&fence);
> > +    if (ret)
> > +        goto out_unlock;
> > +
> > +    ret = nouveau_fence_emit(fence, chan);
> > +    if (ret) {
> > +        nouveau_fence_unref(&fence);
> > +        goto out_unlock;
> >       }
> > +
> > +    /* TODO: figure out a better solution here
> > +     *
> > +     * wait on the fence here explicitly as going through
> > +     * ttm_bo_move_accel_cleanup somehow doesn't seem to do it.
> > +     *
> > +     * Without this the operation can timeout and we'll fallback to a
> > +     * software copy, which might take several minutes to finish.
> > +     */
> > +    nouveau_fence_wait(fence, false, false);
> > +    ret = ttm_bo_move_accel_cleanup(bo, &fence->base, evict, false,
> > +                    new_reg);
> > +    nouveau_fence_unref(&fence);
> > +
> > +out_unlock:
> >       mutex_unlock(&cli->mutex);
> >       return ret;
> >   }
> > diff --git a/drivers/gpu/drm/nouveau/nouveau_chan.c 
> > b/drivers/gpu/drm/nouveau/nouveau_chan.c
> > index 6d639314250a..f69be4c8f9f2 100644
> > --- a/drivers/gpu/drm/nouveau/nouveau_chan.c
> > +++ b/drivers/gpu/drm/nouveau/nouveau_chan.c
> > @@ -62,9 +62,11 @@ nouveau_channel_idle(struct nouveau_channel *chan)
> >           struct nouveau_fence *fence = NULL;
> >           int ret;
> > -        ret = nouveau_fence_new(chan, false, &fence);
> > +        ret = nouveau_fence_new(&fence);
> >           if (!ret) {
> > -            ret = nouveau_fence_wait(fence, false, false);
> > +            ret = nouveau_fence_emit(fence, chan);
> > +            if (!ret)
> > +                ret = nouveau_fence_wait(fence, false, false);
> >               nouveau_fence_unref(&fence);
> >           }
> > diff --git a/drivers/gpu/drm/nouveau/nouveau_dmem.c 
> > b/drivers/gpu/drm/nouveau/nouveau_dmem.c
> > index 789857faa048..4ad40e42cae1 100644
> > --- a/drivers/gpu/drm/nouveau/nouveau_dmem.c
> > +++ b/drivers/gpu/drm/nouveau/nouveau_dmem.c
> > @@ -209,7 +209,8 @@ static vm_fault_t 
> > nouveau_dmem_migrate_to_ram(struct vm_fault *vmf)
> >           goto done;
> >       }
> > -    nouveau_fence_new(dmem->migrate.chan, false, &fence);
> > +    if (!nouveau_fence_new(&fence))
> > +        nouveau_fence_emit(fence, dmem->migrate.chan);
> >       migrate_vma_pages(&args);
> >       nouveau_dmem_fence_done(&fence);
> >       dma_unmap_page(drm->dev->dev, dma_addr, PAGE_SIZE, 
> > DMA_BIDIRECTIONAL);
> > @@ -402,7 +403,8 @@ nouveau_dmem_evict_chunk(struct nouveau_dmem_chunk 
> > *chunk)
> >           }
> >       }
> > -    nouveau_fence_new(chunk->drm->dmem->migrate.chan, false, &fence);
> > +    if (!nouveau_fence_new(&fence))
> > +        nouveau_fence_emit(fence, chunk->drm->dmem->migrate.chan);
> >       migrate_device_pages(src_pfns, dst_pfns, npages);
> >       nouveau_dmem_fence_done(&fence);
> >       migrate_device_finalize(src_pfns, dst_pfns, npages);
> > @@ -675,7 +677,8 @@ static void nouveau_dmem_migrate_chunk(struct 
> > nouveau_drm *drm,
> >           addr += PAGE_SIZE;
> >       }
> > -    nouveau_fence_new(drm->dmem->migrate.chan, false, &fence);
> > +    if (!nouveau_fence_new(&fence))
> > +        nouveau_fence_emit(fence, chunk->drm->dmem->migrate.chan);
> >       migrate_vma_pages(args);
> >       nouveau_dmem_fence_done(&fence);
> >       nouveau_pfns_map(svmm, args->vma->vm_mm, args->start, pfns, i);
> > diff --git a/drivers/gpu/drm/nouveau/nouveau_fence.c 
> > b/drivers/gpu/drm/nouveau/nouveau_fence.c
> > index ee5e9d40c166..e946408f945b 100644
> > --- a/drivers/gpu/drm/nouveau/nouveau_fence.c
> > +++ b/drivers/gpu/drm/nouveau/nouveau_fence.c
> > @@ -210,6 +210,9 @@ nouveau_fence_emit(struct nouveau_fence *fence, 
> > struct nouveau_channel *chan)
> >       struct nouveau_fence_priv *priv = (void*)chan->drm->fence;
> >       int ret;
> > +    if (unlikely(!chan->fence))
> > +        return -ENODEV;
> > +
> >       fence->channel  = chan;
> >       fence->timeout  = jiffies + (15 * HZ);
> > @@ -396,25 +399,16 @@ nouveau_fence_unref(struct nouveau_fence **pfence)
> >   }
> >   int
> > -nouveau_fence_new(struct nouveau_channel *chan, bool sysmem,
> > -          struct nouveau_fence **pfence)
> > +nouveau_fence_new(struct nouveau_fence **pfence)
> >   {
> >       struct nouveau_fence *fence;
> > -    int ret = 0;
> > -
> > -    if (unlikely(!chan->fence))
> > -        return -ENODEV;
> >       fence = kzalloc(sizeof(*fence), GFP_KERNEL);
> >       if (!fence)
> >           return -ENOMEM;
> > -    ret = nouveau_fence_emit(fence, chan);
> > -    if (ret)
> > -        nouveau_fence_unref(&fence);
> > -
> >       *pfence = fence;
> > -    return ret;
> > +    return 0;
> >   }
> >   static const char *nouveau_fence_get_get_driver_name(struct 
> > dma_fence *fence)
> > diff --git a/drivers/gpu/drm/nouveau/nouveau_fence.h 
> > b/drivers/gpu/drm/nouveau/nouveau_fence.h
> > index 0ca2bc85adf6..7c73c7c9834a 100644
> > --- a/drivers/gpu/drm/nouveau/nouveau_fence.h
> > +++ b/drivers/gpu/drm/nouveau/nouveau_fence.h
> > @@ -17,8 +17,7 @@ struct nouveau_fence {
> >       unsigned long timeout;
> >   };
> > -int  nouveau_fence_new(struct nouveau_channel *, bool sysmem,
> > -               struct nouveau_fence **);
> > +int  nouveau_fence_new(struct nouveau_fence **);
> >   void nouveau_fence_unref(struct nouveau_fence **);
> >   int  nouveau_fence_emit(struct nouveau_fence *, struct 
> > nouveau_channel *);
> > diff --git a/drivers/gpu/drm/nouveau/nouveau_gem.c 
> > b/drivers/gpu/drm/nouveau/nouveau_gem.c
> > index a48f42aaeab9..9c8d1b911a01 100644
> > --- a/drivers/gpu/drm/nouveau/nouveau_gem.c
> > +++ b/drivers/gpu/drm/nouveau/nouveau_gem.c
> > @@ -873,8 +873,11 @@ nouveau_gem_ioctl_pushbuf(struct drm_device *dev, 
> > void *data,
> >           }
> >       }
> > -    ret = nouveau_fence_new(chan, false, &fence);
> > +    ret = nouveau_fence_new(&fence);
> > +    if (!ret)
> > +        ret = nouveau_fence_emit(fence, chan);
> >       if (ret) {
> > +        nouveau_fence_unref(&fence);
> >           NV_PRINTK(err, cli, "error fencing pushbuf: %d\n", ret);
> >           WIND_RING(chan);
> >           goto out;