Re: [PATCH 1/5] drm/ttm: use a static ttm_mem_global instance

[Christian König <ckoenig.leichtzumerken@xxxxxxxxx>]

Am 23.10.18 um 08:22 schrieb Thomas Zimmermann:
> Hi Christian
>
> Am 19.10.18 um 18:41 schrieb Christian König:
> > As the name says we only need one global instance of ttm_mem_global.
> >
> > Drop all the driver initialization and just use a single exported
> > instance which is initialized during BO global initialization.
> >
> > Signed-off-by: Christian König <christian.koenig@xxxxxxx>
> > ---
> >   drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c         | 44 -------------------------
> >   drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.h         |  1 -
> >   drivers/gpu/drm/ast/ast_drv.h                   |  1 -
> >   drivers/gpu/drm/ast/ast_ttm.c                   | 32 ++----------------
> >   drivers/gpu/drm/bochs/bochs.h                   |  1 -
> >   drivers/gpu/drm/bochs/bochs_mm.c                | 30 ++---------------
> >   drivers/gpu/drm/cirrus/cirrus_drv.h             |  1 -
> >   drivers/gpu/drm/cirrus/cirrus_ttm.c             | 32 ++----------------
> >   drivers/gpu/drm/hisilicon/hibmc/hibmc_drm_drv.h |  1 -
> >   drivers/gpu/drm/hisilicon/hibmc/hibmc_ttm.c     | 31 +++--------------
> >   drivers/gpu/drm/mgag200/mgag200_drv.h           |  1 -
> >   drivers/gpu/drm/mgag200/mgag200_ttm.c           | 32 ++----------------
> >   drivers/gpu/drm/nouveau/nouveau_drv.h           |  1 -
> >   drivers/gpu/drm/nouveau/nouveau_ttm.c           | 34 ++-----------------
> >   drivers/gpu/drm/qxl/qxl_drv.h                   |  1 -
> >   drivers/gpu/drm/qxl/qxl_ttm.c                   | 28 ----------------
> >   drivers/gpu/drm/radeon/radeon.h                 |  1 -
> >   drivers/gpu/drm/radeon/radeon_ttm.c             | 26 ---------------
> >   drivers/gpu/drm/ttm/ttm_bo.c                    | 10 ++++--
> >   drivers/gpu/drm/ttm/ttm_memory.c                |  5 +--
> >   drivers/gpu/drm/virtio/virtgpu_drv.h            |  1 -
> >   drivers/gpu/drm/virtio/virtgpu_ttm.c            | 27 ---------------
> >   drivers/gpu/drm/vmwgfx/vmwgfx_drv.c             |  4 +--
> >   drivers/gpu/drm/vmwgfx/vmwgfx_drv.h             |  3 +-
> >   drivers/gpu/drm/vmwgfx/vmwgfx_ttm_glue.c        | 27 ---------------
> >   drivers/staging/vboxvideo/vbox_drv.h            |  1 -
> >   drivers/staging/vboxvideo/vbox_ttm.c            | 24 --------------
> >   include/drm/ttm/ttm_bo_driver.h                 |  8 ++---
> >   include/drm/ttm/ttm_memory.h                    |  4 +--
> >   29 files changed, 32 insertions(+), 380 deletions(-)
> Great that you removed all the global TTM state from all the drivers.
> This removes a lot of duplication and simplifies driver development a bit.
>
>
> > diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
> > index 9edece6510d3..3006050b1720 100644
> > --- a/drivers/gpu/drm/ttm/ttm_bo.c
> > +++ b/drivers/gpu/drm/ttm/ttm_bo.c
> > @@ -1526,18 +1526,22 @@ void ttm_bo_global_release(struct ttm_bo_global *glob)
> >   {
> >   	kobject_del(&glob->kobj);
> >   	kobject_put(&glob->kobj);
> > +	ttm_mem_global_release(&ttm_mem_glob);
> >   }
> >   EXPORT_SYMBOL(ttm_bo_global_release);
> >   
> > -int ttm_bo_global_init(struct ttm_bo_global *glob,
> > -		       struct ttm_mem_global *mem_glob)
> > +int ttm_bo_global_init(struct ttm_bo_global *glob)
> >   {
> >   	int ret;
> >   	unsigned i;
> >   
> > +	ret = ttm_mem_global_init(&ttm_mem_glob);
> > +	if (ret)
> > +		return ret;
> > +
> What I really dislike about this patch set is that it mixes state and
> implementation into that same functions. The original code had a fairly
> good separation of both. Now the mechanisms and policies are located in
> the same places.[^1]
>
> This looks like a simplification, but from my experience, such code is a
> setup for long-term maintenance problems. For example, I can imagine
> that someone at some point wants multiple global buffers (e.g., on a
> NUMA-like architecture).

That is exactly the thinking which messed up things in the first place. 
Keep in mind that this is the kernel and not a userspace C++ project.

Handling this as global state in a module is perfectly and we already 
support NUMA use cases with this. E.g. if we would have this state 
multiple times I would actually consider this a bug.

So pushing this into a structure makes it much more error prone and 
doesn't buy us anything.

In the long term I'm actually thinking about getting completely rid of 
the ttm_mem_global and ttm_bo_global and just use static variables for this.

Regards,
Christian.

> I understand that I'm new here, have no say, and probably don't get the
> big picture, but from my point of view, this is not a forward-thinking
> change.
>
> Best regards
> Thomas
>
> [^1] More philosophically speaking, program state can be global, but
> data structures can only be share-able. ttm_mem_global and ttm_bo_global
> should be renamed to something like ttm_shared_mem, rsp. ttm_shared_bo.
>
>
> >   	mutex_init(&glob->device_list_mutex);
> >   	spin_lock_init(&glob->lru_lock);
> > -	glob->mem_glob = mem_glob;
> > +	glob->mem_glob = &ttm_mem_glob;
> >   	glob->mem_glob->bo_glob = glob;
> >   	glob->dummy_read_page = alloc_page(__GFP_ZERO | GFP_DMA32);
> >   
> > diff --git a/drivers/gpu/drm/ttm/ttm_memory.c b/drivers/gpu/drm/ttm/ttm_memory.c
> > index 450387c92b63..7704e17c402f 100644
> > --- a/drivers/gpu/drm/ttm/ttm_memory.c
> > +++ b/drivers/gpu/drm/ttm/ttm_memory.c
> > @@ -41,6 +41,9 @@
> >   
> >   #define TTM_MEMORY_ALLOC_RETRIES 4
> >   
> > +struct ttm_mem_global ttm_mem_glob;
> > +EXPORT_SYMBOL(ttm_mem_glob);
> > +
> >   struct ttm_mem_zone {
> >   	struct kobject kobj;
> >   	struct ttm_mem_global *glob;
> > @@ -464,7 +467,6 @@ int ttm_mem_global_init(struct ttm_mem_global *glob)
> >   	ttm_mem_global_release(glob);
> >   	return ret;
> >   }
> > -EXPORT_SYMBOL(ttm_mem_global_init);
> >   
> >   void ttm_mem_global_release(struct ttm_mem_global *glob)
> >   {
> > @@ -486,7 +488,6 @@ void ttm_mem_global_release(struct ttm_mem_global *glob)
> >   	kobject_del(&glob->kobj);
> >   	kobject_put(&glob->kobj);
> >   }
> > -EXPORT_SYMBOL(ttm_mem_global_release);
> >   
> >   static void ttm_check_swapping(struct ttm_mem_global *glob)
> >   {
> > diff --git a/drivers/gpu/drm/virtio/virtgpu_drv.h b/drivers/gpu/drm/virtio/virtgpu_drv.h
> > index 65605e207bbe..dec42d421e00 100644
> > --- a/drivers/gpu/drm/virtio/virtgpu_drv.h
> > +++ b/drivers/gpu/drm/virtio/virtgpu_drv.h
> > @@ -133,7 +133,6 @@ struct virtio_gpu_framebuffer {
> >   
> >   struct virtio_gpu_mman {
> >   	struct ttm_bo_global_ref        bo_global_ref;
> > -	struct drm_global_reference	mem_global_ref;
> >   	bool				mem_global_referenced;
> >   	struct ttm_bo_device		bdev;
> >   };
> > diff --git a/drivers/gpu/drm/virtio/virtgpu_ttm.c b/drivers/gpu/drm/virtio/virtgpu_ttm.c
> > index 0ec46b47b423..b99ecc6d97d3 100644
> > --- a/drivers/gpu/drm/virtio/virtgpu_ttm.c
> > +++ b/drivers/gpu/drm/virtio/virtgpu_ttm.c
> > @@ -50,37 +50,12 @@ virtio_gpu_device *virtio_gpu_get_vgdev(struct ttm_bo_device *bdev)
> >   	return vgdev;
> >   }
> >   
> > -static int virtio_gpu_ttm_mem_global_init(struct drm_global_reference *ref)
> > -{
> > -	return ttm_mem_global_init(ref->object);
> > -}
> > -
> > -static void virtio_gpu_ttm_mem_global_release(struct drm_global_reference *ref)
> > -{
> > -	ttm_mem_global_release(ref->object);
> > -}
> > -
> >   static int virtio_gpu_ttm_global_init(struct virtio_gpu_device *vgdev)
> >   {
> >   	struct drm_global_reference *global_ref;
> >   	int r;
> >   
> >   	vgdev->mman.mem_global_referenced = false;
> > -	global_ref = &vgdev->mman.mem_global_ref;
> > -	global_ref->global_type = DRM_GLOBAL_TTM_MEM;
> > -	global_ref->size = sizeof(struct ttm_mem_global);
> > -	global_ref->init = &virtio_gpu_ttm_mem_global_init;
> > -	global_ref->release = &virtio_gpu_ttm_mem_global_release;
> > -
> > -	r = drm_global_item_ref(global_ref);
> > -	if (r != 0) {
> > -		DRM_ERROR("Failed setting up TTM memory accounting "
> > -			  "subsystem.\n");
> > -		return r;
> > -	}
> > -
> > -	vgdev->mman.bo_global_ref.mem_glob =
> > -		vgdev->mman.mem_global_ref.object;
> >   	global_ref = &vgdev->mman.bo_global_ref.ref;
> >   	global_ref->global_type = DRM_GLOBAL_TTM_BO;
> >   	global_ref->size = sizeof(struct ttm_bo_global);
> > @@ -89,7 +64,6 @@ static int virtio_gpu_ttm_global_init(struct virtio_gpu_device *vgdev)
> >   	r = drm_global_item_ref(global_ref);
> >   	if (r != 0) {
> >   		DRM_ERROR("Failed setting up TTM BO subsystem.\n");
> > -		drm_global_item_unref(&vgdev->mman.mem_global_ref);
> >   		return r;
> >   	}
> >   
> > @@ -101,7 +75,6 @@ static void virtio_gpu_ttm_global_fini(struct virtio_gpu_device *vgdev)
> >   {
> >   	if (vgdev->mman.mem_global_referenced) {
> >   		drm_global_item_unref(&vgdev->mman.bo_global_ref.ref);
> > -		drm_global_item_unref(&vgdev->mman.mem_global_ref);
> >   		vgdev->mman.mem_global_referenced = false;
> >   	}
> >   }
> > diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_drv.c b/drivers/gpu/drm/vmwgfx/vmwgfx_drv.c
> > index bb6dbbe18835..57df776d987c 100644
> > --- a/drivers/gpu/drm/vmwgfx/vmwgfx_drv.c
> > +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_drv.c
> > @@ -828,8 +828,8 @@ static int vmw_driver_load(struct drm_device *dev, unsigned long chipset)
> >   		goto out_err4;
> >   	}
> >   
> > -	dev_priv->tdev = ttm_object_device_init
> > -		(dev_priv->mem_global_ref.object, 12, &vmw_prime_dmabuf_ops);
> > +	dev_priv->tdev = ttm_object_device_init(&ttm_mem_glob, 12,
> > +						&vmw_prime_dmabuf_ops);
> >   
> >   	if (unlikely(dev_priv->tdev == NULL)) {
> >   		DRM_ERROR("Unable to initialize TTM object management.\n");
> > diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_drv.h b/drivers/gpu/drm/vmwgfx/vmwgfx_drv.h
> > index 1abe21758b0d..df15a745efc3 100644
> > --- a/drivers/gpu/drm/vmwgfx/vmwgfx_drv.h
> > +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_drv.h
> > @@ -366,7 +366,6 @@ enum {
> >   struct vmw_private {
> >   	struct ttm_bo_device bdev;
> >   	struct ttm_bo_global_ref bo_global_ref;
> > -	struct drm_global_reference mem_global_ref;
> >   
> >   	struct vmw_fifo_state fifo;
> >   
> > @@ -1288,7 +1287,7 @@ vmw_bo_reference(struct vmw_buffer_object *buf)
> >   
> >   static inline struct ttm_mem_global *vmw_mem_glob(struct vmw_private *dev_priv)
> >   {
> > -	return (struct ttm_mem_global *) dev_priv->mem_global_ref.object;
> > +	return &ttm_mem_glob;
> >   }
> >   
> >   static inline void vmw_fifo_resource_inc(struct vmw_private *dev_priv)
> > diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_ttm_glue.c b/drivers/gpu/drm/vmwgfx/vmwgfx_ttm_glue.c
> > index f3ce43c41978..0ac473cd5136 100644
> > --- a/drivers/gpu/drm/vmwgfx/vmwgfx_ttm_glue.c
> > +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_ttm_glue.c
> > @@ -43,36 +43,11 @@ int vmw_mmap(struct file *filp, struct vm_area_struct *vma)
> >   	return ttm_bo_mmap(filp, vma, &dev_priv->bdev);
> >   }
> >   
> > -static int vmw_ttm_mem_global_init(struct drm_global_reference *ref)
> > -{
> > -	DRM_INFO("global init.\n");
> > -	return ttm_mem_global_init(ref->object);
> > -}
> > -
> > -static void vmw_ttm_mem_global_release(struct drm_global_reference *ref)
> > -{
> > -	ttm_mem_global_release(ref->object);
> > -}
> > -
> >   int vmw_ttm_global_init(struct vmw_private *dev_priv)
> >   {
> >   	struct drm_global_reference *global_ref;
> >   	int ret;
> >   
> > -	global_ref = &dev_priv->mem_global_ref;
> > -	global_ref->global_type = DRM_GLOBAL_TTM_MEM;
> > -	global_ref->size = sizeof(struct ttm_mem_global);
> > -	global_ref->init = &vmw_ttm_mem_global_init;
> > -	global_ref->release = &vmw_ttm_mem_global_release;
> > -
> > -	ret = drm_global_item_ref(global_ref);
> > -	if (unlikely(ret != 0)) {
> > -		DRM_ERROR("Failed setting up TTM memory accounting.\n");
> > -		return ret;
> > -	}
> > -
> > -	dev_priv->bo_global_ref.mem_glob =
> > -		dev_priv->mem_global_ref.object;
> >   	global_ref = &dev_priv->bo_global_ref.ref;
> >   	global_ref->global_type = DRM_GLOBAL_TTM_BO;
> >   	global_ref->size = sizeof(struct ttm_bo_global);
> > @@ -87,12 +62,10 @@ int vmw_ttm_global_init(struct vmw_private *dev_priv)
> >   
> >   	return 0;
> >   out_no_bo:
> > -	drm_global_item_unref(&dev_priv->mem_global_ref);
> >   	return ret;
> >   }
> >   
> >   void vmw_ttm_global_release(struct vmw_private *dev_priv)
> >   {
> >   	drm_global_item_unref(&dev_priv->bo_global_ref.ref);
> > -	drm_global_item_unref(&dev_priv->mem_global_ref);
> >   }
> > diff --git a/drivers/staging/vboxvideo/vbox_drv.h b/drivers/staging/vboxvideo/vbox_drv.h
> > index 594f84272957..41f760b77704 100644
> > --- a/drivers/staging/vboxvideo/vbox_drv.h
> > +++ b/drivers/staging/vboxvideo/vbox_drv.h
> > @@ -95,7 +95,6 @@ struct vbox_private {
> >   	int fb_mtrr;
> >   
> >   	struct {
> > -		struct drm_global_reference mem_global_ref;
> >   		struct ttm_bo_global_ref bo_global_ref;
> >   		struct ttm_bo_device bdev;
> >   	} ttm;
> > diff --git a/drivers/staging/vboxvideo/vbox_ttm.c b/drivers/staging/vboxvideo/vbox_ttm.c
> > index 2329a55d4636..88cdacf2b0f0 100644
> > --- a/drivers/staging/vboxvideo/vbox_ttm.c
> > +++ b/drivers/staging/vboxvideo/vbox_ttm.c
> > @@ -35,16 +35,6 @@ static inline struct vbox_private *vbox_bdev(struct ttm_bo_device *bd)
> >   	return container_of(bd, struct vbox_private, ttm.bdev);
> >   }
> >   
> > -static int vbox_ttm_mem_global_init(struct drm_global_reference *ref)
> > -{
> > -	return ttm_mem_global_init(ref->object);
> > -}
> > -
> > -static void vbox_ttm_mem_global_release(struct drm_global_reference *ref)
> > -{
> > -	ttm_mem_global_release(ref->object);
> > -}
> > -
> >   /**
> >    * Adds the vbox memory manager object/structures to the global memory manager.
> >    */
> > @@ -53,18 +43,6 @@ static int vbox_ttm_global_init(struct vbox_private *vbox)
> >   	struct drm_global_reference *global_ref;
> >   	int ret;
> >   
> > -	global_ref = &vbox->ttm.mem_global_ref;
> > -	global_ref->global_type = DRM_GLOBAL_TTM_MEM;
> > -	global_ref->size = sizeof(struct ttm_mem_global);
> > -	global_ref->init = &vbox_ttm_mem_global_init;
> > -	global_ref->release = &vbox_ttm_mem_global_release;
> > -	ret = drm_global_item_ref(global_ref);
> > -	if (ret) {
> > -		DRM_ERROR("Failed setting up TTM memory subsystem.\n");
> > -		return ret;
> > -	}
> > -
> > -	vbox->ttm.bo_global_ref.mem_glob = vbox->ttm.mem_global_ref.object;
> >   	global_ref = &vbox->ttm.bo_global_ref.ref;
> >   	global_ref->global_type = DRM_GLOBAL_TTM_BO;
> >   	global_ref->size = sizeof(struct ttm_bo_global);
> > @@ -74,7 +52,6 @@ static int vbox_ttm_global_init(struct vbox_private *vbox)
> >   	ret = drm_global_item_ref(global_ref);
> >   	if (ret) {
> >   		DRM_ERROR("Failed setting up TTM BO subsystem.\n");
> > -		drm_global_item_unref(&vbox->ttm.mem_global_ref);
> >   		return ret;
> >   	}
> >   
> > @@ -87,7 +64,6 @@ static int vbox_ttm_global_init(struct vbox_private *vbox)
> >   static void vbox_ttm_global_release(struct vbox_private *vbox)
> >   {
> >   	drm_global_item_unref(&vbox->ttm.bo_global_ref.ref);
> > -	drm_global_item_unref(&vbox->ttm.mem_global_ref);
> >   }
> >   
> >   static void vbox_bo_ttm_destroy(struct ttm_buffer_object *tbo)
> > diff --git a/include/drm/ttm/ttm_bo_driver.h b/include/drm/ttm/ttm_bo_driver.h
> > index c6ee07d10281..4ae6fc33f761 100644
> > --- a/include/drm/ttm/ttm_bo_driver.h
> > +++ b/include/drm/ttm/ttm_bo_driver.h
> > @@ -570,8 +570,7 @@ void ttm_bo_mem_put_locked(struct ttm_buffer_object *bo,
> >   			   struct ttm_mem_reg *mem);
> >   
> >   void ttm_bo_global_release(struct ttm_bo_global *glob);
> > -int ttm_bo_global_init(struct ttm_bo_global *glob,
> > -		       struct ttm_mem_global *mem_glob);
> > +int ttm_bo_global_init(struct ttm_bo_global *glob);
> >   
> >   int ttm_bo_device_release(struct ttm_bo_device *bdev);
> >   
> > @@ -895,7 +894,6 @@ extern const struct ttm_mem_type_manager_func ttm_bo_manager_func;
> >   
> >   struct ttm_bo_global_ref {
> >   	struct drm_global_reference ref;
> > -	struct ttm_mem_global *mem_glob;
> >   };
> >   
> >   /**
> > @@ -909,9 +907,7 @@ struct ttm_bo_global_ref {
> >    */
> >   static inline int ttm_bo_global_ref_init(struct drm_global_reference *ref)
> >   {
> > -	struct ttm_bo_global_ref *bo_ref =
> > -		container_of(ref, struct ttm_bo_global_ref, ref);
> > -	return ttm_bo_global_init(ref->object, bo_ref->mem_glob);
> > +	return ttm_bo_global_init(ref->object);
> >   }
> >   
> >   /**
> > diff --git a/include/drm/ttm/ttm_memory.h b/include/drm/ttm/ttm_memory.h
> > index 737b5fed8003..3ff48a0a2d7b 100644
> > --- a/include/drm/ttm/ttm_memory.h
> > +++ b/include/drm/ttm/ttm_memory.h
> > @@ -63,7 +63,7 @@
> >   
> >   #define TTM_MEM_MAX_ZONES 2
> >   struct ttm_mem_zone;
> > -struct ttm_mem_global {
> > +extern struct ttm_mem_global {
> >   	struct kobject kobj;
> >   	struct ttm_bo_global *bo_glob;
> >   	struct workqueue_struct *swap_queue;
> > @@ -78,7 +78,7 @@ struct ttm_mem_global {
> >   #else
> >   	struct ttm_mem_zone *zone_dma32;
> >   #endif
> > -};
> > +} ttm_mem_glob;
> >   
> >   extern int ttm_mem_global_init(struct ttm_mem_global *glob);
> >   extern void ttm_mem_global_release(struct ttm_mem_global *glob);

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