Re: [RFC 03/10] drm/i915/vm_bind: Support private and shared BOs

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Am 08.07.22 um 15:23 schrieb Niranjana Vishwanathapura:
On Thu, Jul 07, 2022 at 03:27:43PM +0200, Christian König wrote:
Am 02.07.22 um 00:50 schrieb Niranjana Vishwanathapura:
Add uapi allowing user to specify a BO as private to a specified VM
during the BO creation.
VM private BOs can only be mapped on the specified VM and can't be
dma_buf exported. VM private BOs share a single common dma_resv object,
hence has a performance advantage requiring a single dma_resv object
update in the execbuf path compared to non-private (shared) BOs.

Sounds like you picked up the per VM BO idea from amdgpu here :)

Of hand looks like a good idea, but shouldn't we add a few comments in the common documentation about that?

E.g. something like "Multiple buffer objects sometimes share the same dma_resv object....." to the dma_resv documentation.

Probably best as a separate patch after this here has landed.

:)
Sounds good. Probably we need to update documentation of
drm_gem_object.resv and drm_gem_object._resv here, right?

Yes, I would also add a word or two to the dma_resv object. Something like "Multiple buffers are sometimes using a single dma_resv object..."

Christian.


Doing it in a separate patch after this series lands sounds good to me.

Thanks,
Niranjana


Regards,
Christian.


Signed-off-by: Niranjana Vishwanathapura <niranjana.vishwanathapura@xxxxxxxxx>
---
 drivers/gpu/drm/i915/gem/i915_gem_create.c    | 41 ++++++++++++++++++-
 drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c    |  6 +++
 .../gpu/drm/i915/gem/i915_gem_object_types.h  |  3 ++
 drivers/gpu/drm/i915/gem/i915_gem_ttm.c       |  3 ++
 drivers/gpu/drm/i915/gem/i915_gem_vm_bind.h   | 11 +++++
 .../drm/i915/gem/i915_gem_vm_bind_object.c    |  9 ++++
 drivers/gpu/drm/i915/gt/intel_gtt.c           |  4 ++
 drivers/gpu/drm/i915/gt/intel_gtt.h           |  2 +
 drivers/gpu/drm/i915/i915_vma.c               |  1 +
 drivers/gpu/drm/i915/i915_vma_types.h         |  2 +
 include/uapi/drm/i915_drm.h                   | 30 ++++++++++++++
 11 files changed, 110 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_create.c b/drivers/gpu/drm/i915/gem/i915_gem_create.c
index 927a87e5ec59..7e264566b51f 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_create.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_create.c
@@ -11,6 +11,7 @@
 #include "pxp/intel_pxp.h"
 #include "i915_drv.h"
+#include "i915_gem_context.h"
 #include "i915_gem_create.h"
 #include "i915_trace.h"
 #include "i915_user_extensions.h"
@@ -243,6 +244,7 @@ struct create_ext {
     unsigned int n_placements;
     unsigned int placement_mask;
     unsigned long flags;
+    u32 vm_id;
 };
 static void repr_placements(char *buf, size_t size,
@@ -392,9 +394,24 @@ static int ext_set_protected(struct i915_user_extension __user *base, void *data
     return 0;
 }
+static int ext_set_vm_private(struct i915_user_extension __user *base,
+                  void *data)
+{
+    struct drm_i915_gem_create_ext_vm_private ext;
+    struct create_ext *ext_data = data;
+
+    if (copy_from_user(&ext, base, sizeof(ext)))
+        return -EFAULT;
+
+    ext_data->vm_id = ext.vm_id;
+
+    return 0;
+}
+
 static const i915_user_extension_fn create_extensions[] = {
     [I915_GEM_CREATE_EXT_MEMORY_REGIONS] = ext_set_placements,
     [I915_GEM_CREATE_EXT_PROTECTED_CONTENT] = ext_set_protected,
+    [I915_GEM_CREATE_EXT_VM_PRIVATE] = ext_set_vm_private,
 };
 /**
@@ -410,6 +427,7 @@ i915_gem_create_ext_ioctl(struct drm_device *dev, void *data,
     struct drm_i915_private *i915 = to_i915(dev);
     struct drm_i915_gem_create_ext *args = data;
     struct create_ext ext_data = { .i915 = i915 };
+    struct i915_address_space *vm = NULL;
     struct drm_i915_gem_object *obj;
     int ret;
@@ -423,6 +441,12 @@ i915_gem_create_ext_ioctl(struct drm_device *dev, void *data,
     if (ret)
         return ret;
+    if (ext_data.vm_id) {
+        vm = i915_gem_vm_lookup(file->driver_priv, ext_data.vm_id);
+        if (unlikely(!vm))
+            return -ENOENT;
+    }
+
     if (!ext_data.n_placements) {
         ext_data.placements[0] =
             intel_memory_region_by_type(i915, INTEL_MEMORY_SYSTEM);
@@ -449,8 +473,21 @@ i915_gem_create_ext_ioctl(struct drm_device *dev, void *data,
                         ext_data.placements,
                         ext_data.n_placements,
                         ext_data.flags);
-    if (IS_ERR(obj))
-        return PTR_ERR(obj);
+    if (IS_ERR(obj)) {
+        ret = PTR_ERR(obj);
+        goto vm_put;
+    }
+
+    if (vm) {
+        obj->base.resv = vm->root_obj->base.resv;
+        obj->priv_root = i915_gem_object_get(vm->root_obj);
+        i915_vm_put(vm);
+    }
     return i915_gem_publish(obj, file, &args->size, &args->handle);
+vm_put:
+    if (vm)
+        i915_vm_put(vm);
+
+    return ret;
 }
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
index f5062d0c6333..6433173c3e84 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
@@ -218,6 +218,12 @@ struct dma_buf *i915_gem_prime_export(struct drm_gem_object *gem_obj, int flags)
     struct drm_i915_gem_object *obj = to_intel_bo(gem_obj);
     DEFINE_DMA_BUF_EXPORT_INFO(exp_info);
+    if (obj->priv_root) {
+        drm_dbg(obj->base.dev,
+            "Exporting VM private objects is not allowed\n");
+        return ERR_PTR(-EINVAL);
+    }
+
     exp_info.ops = &i915_dmabuf_ops;
     exp_info.size = gem_obj->size;
     exp_info.flags = flags;
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object_types.h b/drivers/gpu/drm/i915/gem/i915_gem_object_types.h
index 5cf36a130061..9fe3395ad4d9 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_object_types.h
+++ b/drivers/gpu/drm/i915/gem/i915_gem_object_types.h
@@ -241,6 +241,9 @@ struct drm_i915_gem_object {
     const struct drm_i915_gem_object_ops *ops;
+    /* Shared root is object private to a VM; NULL otherwise */
+    struct drm_i915_gem_object *priv_root;
+
     struct {
         /**
          * @vma.lock: protect the list/tree of vmas
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
index 7e1f8b83077f..f1912b12db00 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
@@ -1152,6 +1152,9 @@ void i915_ttm_bo_destroy(struct ttm_buffer_object *bo)
     i915_gem_object_release_memory_region(obj);
     mutex_destroy(&obj->ttm.get_io_page.lock);
+    if (obj->priv_root)
+        i915_gem_object_put(obj->priv_root);
+
     if (obj->ttm.created) {
         /*
          * We freely manage the shrinker LRU outide of the mm.pages life diff --git a/drivers/gpu/drm/i915/gem/i915_gem_vm_bind.h b/drivers/gpu/drm/i915/gem/i915_gem_vm_bind.h
index 642cdb559f17..ee6e4c52e80e 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_vm_bind.h
+++ b/drivers/gpu/drm/i915/gem/i915_gem_vm_bind.h
@@ -26,6 +26,17 @@ static inline void i915_gem_vm_bind_unlock(struct i915_address_space *vm)
     mutex_unlock(&vm->vm_bind_lock);
 }
+static inline int i915_gem_vm_priv_lock(struct i915_address_space *vm,
+                    struct i915_gem_ww_ctx *ww)
+{
+    return i915_gem_object_lock(vm->root_obj, ww);
+}
+
+static inline void i915_gem_vm_priv_unlock(struct i915_address_space *vm)
+{
+    i915_gem_object_unlock(vm->root_obj);
+}
+
 struct i915_vma *
 i915_gem_vm_bind_lookup_vma(struct i915_address_space *vm, u64 va);
 void i915_gem_vm_bind_remove(struct i915_vma *vma, bool release_obj);
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 43ceb4dcca6c..3201204c8e74 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
@@ -85,6 +85,7 @@ void i915_gem_vm_bind_remove(struct i915_vma *vma, bool release_obj)
     if (!list_empty(&vma->vm_bind_link)) {
         list_del_init(&vma->vm_bind_link);
+        list_del_init(&vma->non_priv_vm_bind_link);
         i915_vm_bind_it_remove(vma, &vma->vm->va);
         /* Release object */
@@ -185,6 +186,11 @@ int i915_gem_vm_bind_obj(struct i915_address_space *vm,
         goto put_obj;
     }
+    if (obj->priv_root && obj->priv_root != vm->root_obj) {
+        ret = -EINVAL;
+        goto put_obj;
+    }
+
     ret = i915_gem_vm_bind_lock_interruptible(vm);
     if (ret)
         goto put_obj;
@@ -211,6 +217,9 @@ int i915_gem_vm_bind_obj(struct i915_address_space *vm,
     list_add_tail(&vma->vm_bind_link, &vm->vm_bound_list);
     i915_vm_bind_it_insert(vma, &vm->va);
+    if (!obj->priv_root)
+        list_add_tail(&vma->non_priv_vm_bind_link,
+                  &vm->non_priv_vm_bind_list);
     /* Hold object reference until vm_unbind */
     i915_gem_object_get(vma->obj);
diff --git a/drivers/gpu/drm/i915/gt/intel_gtt.c b/drivers/gpu/drm/i915/gt/intel_gtt.c
index 135dc4a76724..df0a8459c3c6 100644
--- a/drivers/gpu/drm/i915/gt/intel_gtt.c
+++ b/drivers/gpu/drm/i915/gt/intel_gtt.c
@@ -176,6 +176,7 @@ int i915_vm_lock_objects(struct i915_address_space *vm,
 void i915_address_space_fini(struct i915_address_space *vm)
 {
     drm_mm_takedown(&vm->mm);
+    i915_gem_object_put(vm->root_obj);
     GEM_BUG_ON(!RB_EMPTY_ROOT(&vm->va.rb_root));
     mutex_destroy(&vm->vm_bind_lock);
 }
@@ -289,6 +290,9 @@ void i915_address_space_init(struct i915_address_space *vm, int subclass)
     INIT_LIST_HEAD(&vm->vm_bind_list);
     INIT_LIST_HEAD(&vm->vm_bound_list);
     mutex_init(&vm->vm_bind_lock);
+    INIT_LIST_HEAD(&vm->non_priv_vm_bind_list);
+    vm->root_obj = i915_gem_object_create_internal(vm->i915, PAGE_SIZE);
+    GEM_BUG_ON(IS_ERR(vm->root_obj));
 }
 void *__px_vaddr(struct drm_i915_gem_object *p)
diff --git a/drivers/gpu/drm/i915/gt/intel_gtt.h b/drivers/gpu/drm/i915/gt/intel_gtt.h
index d4a6ce65251d..f538ce9115c9 100644
--- a/drivers/gpu/drm/i915/gt/intel_gtt.h
+++ b/drivers/gpu/drm/i915/gt/intel_gtt.h
@@ -267,6 +267,8 @@ struct i915_address_space {
     struct list_head vm_bound_list;
     /* va tree of persistent vmas */
     struct rb_root_cached va;
+    struct list_head non_priv_vm_bind_list;
+    struct drm_i915_gem_object *root_obj;
     /* Global GTT */
     bool is_ggtt:1;
diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
index d324e29cef0a..f0226581d342 100644
--- a/drivers/gpu/drm/i915/i915_vma.c
+++ b/drivers/gpu/drm/i915/i915_vma.c
@@ -236,6 +236,7 @@ vma_create(struct drm_i915_gem_object *obj,
     mutex_unlock(&vm->mutex);
     INIT_LIST_HEAD(&vma->vm_bind_link);
+    INIT_LIST_HEAD(&vma->non_priv_vm_bind_link);
     return vma;
 err_unlock:
diff --git a/drivers/gpu/drm/i915/i915_vma_types.h b/drivers/gpu/drm/i915/i915_vma_types.h
index b6d179bdbfa0..2298b3d6b7c4 100644
--- a/drivers/gpu/drm/i915/i915_vma_types.h
+++ b/drivers/gpu/drm/i915/i915_vma_types.h
@@ -290,6 +290,8 @@ struct i915_vma {
     struct list_head vm_link;
     struct list_head vm_bind_link; /* Link in persistent VMA list */
+    /* Link in non-private persistent VMA list */
+    struct list_head non_priv_vm_bind_link;
     /** Interval tree structures for persistent vma */
     struct rb_node rb;
diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
index 26cca49717f8..ce1c6592b0d7 100644
--- a/include/uapi/drm/i915_drm.h
+++ b/include/uapi/drm/i915_drm.h
@@ -3542,9 +3542,13 @@ struct drm_i915_gem_create_ext {
      *
      * For I915_GEM_CREATE_EXT_PROTECTED_CONTENT usage see
      * struct drm_i915_gem_create_ext_protected_content.
+     *
+     * For I915_GEM_CREATE_EXT_VM_PRIVATE usage see
+     * struct drm_i915_gem_create_ext_vm_private.
      */
 #define I915_GEM_CREATE_EXT_MEMORY_REGIONS 0
 #define I915_GEM_CREATE_EXT_PROTECTED_CONTENT 1
+#define I915_GEM_CREATE_EXT_VM_PRIVATE 2
     __u64 extensions;
 };
@@ -3662,6 +3666,32 @@ struct drm_i915_gem_create_ext_protected_content {  /* ID of the protected content session managed by i915 when PXP is active */
 #define I915_PROTECTED_CONTENT_DEFAULT_SESSION 0xf
+/**
+ * struct drm_i915_gem_create_ext_vm_private - Extension to make the object
+ * private to the specified VM.
+ *
+ * See struct drm_i915_gem_create_ext.
+ *
+ * By default, BOs can be mapped on multiple VMs and can also be dma-buf
+ * exported. Hence these BOs are referred to as Shared BOs.
+ * During each execbuf3 submission, the request fence must be added to the
+ * dma-resv fence list of all shared BOs mapped on the VM.
+ *
+ * Unlike Shared BOs, these VM private BOs can only be mapped on the VM they + * are private to and can't be dma-buf exported. All private BOs of a VM share + * the dma-resv object. Hence during each execbuf3 submission, they need only + * one dma-resv fence list updated. Thus, the fast path (where required + * mappings are already bound) submission latency is O(1) w.r.t the number of
+ * VM private BOs.
+ */
+struct drm_i915_gem_create_ext_vm_private {
+    /** @base: Extension link. See struct i915_user_extension. */
+    struct i915_user_extension base;
+
+    /** @vm_id: Id of the VM to which the object is private */
+    __u32 vm_id;
+};
+
 /**
  * struct drm_i915_gem_vm_bind - VA to object mapping to bind.
  *





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