Message-ID: <c2256c7d-e768-ae3f-d465-b9f8080d111b@amd.com>
Date:   Fri, 27 Jan 2023 08:55:09 +0100
From:   Christian König <christian.koenig@....com>
To:     Danilo Krummrich <dakr@...hat.com>,
        Matthew Brost <matthew.brost@...el.com>
Cc:     daniel@...ll.ch, airlied@...hat.com, bskeggs@...hat.com,
        jason@...kstrand.net, tzimmermann@...e.de, mripard@...nel.org,
        corbet@....net, nouveau@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH drm-next 05/14] drm/nouveau: new VM_BIND uapi interfaces

Am 27.01.23 um 02:26 schrieb Danilo Krummrich:
> On 1/27/23 02:05, Matthew Brost wrote:
>> On Wed, Jan 18, 2023 at 07:12:47AM +0100, Danilo Krummrich wrote:
>>> This commit provides the interfaces for the new UAPI motivated by the
>>> Vulkan API. It allows user mode drivers (UMDs) to:
>>>
>>> 1) Initialize a GPU virtual address (VA) space via the new
>>>     DRM_IOCTL_NOUVEAU_VM_INIT ioctl. UMDs can provide a kernel reserved
>>>     VA area.
>>>
>>> 2) Bind and unbind GPU VA space mappings via the new
>>>     DRM_IOCTL_NOUVEAU_VM_BIND ioctl.
>>>
>>> 3) Execute push buffers with the new DRM_IOCTL_NOUVEAU_EXEC ioctl.
>>>
>>> Both, DRM_IOCTL_NOUVEAU_VM_BIND and DRM_IOCTL_NOUVEAU_EXEC support
>>> asynchronous processing with DRM syncobjs as synchronization mechanism.
>>>
>>> The default DRM_IOCTL_NOUVEAU_VM_BIND is synchronous processing,
>>> DRM_IOCTL_NOUVEAU_EXEC supports asynchronous processing only.
>>>
>>> Co-authored-by: Dave Airlie <airlied@...hat.com>
>>> Signed-off-by: Danilo Krummrich <dakr@...hat.com>
>>> ---
>>>   Documentation/gpu/driver-uapi.rst |   8 ++
>>>   include/uapi/drm/nouveau_drm.h    | 216 
>>> ++++++++++++++++++++++++++++++
>>>   2 files changed, 224 insertions(+)
>>>
>>> diff --git a/Documentation/gpu/driver-uapi.rst 
>>> b/Documentation/gpu/driver-uapi.rst
>>> index 4411e6919a3d..9c7ca6e33a68 100644
>>> --- a/Documentation/gpu/driver-uapi.rst
>>> +++ b/Documentation/gpu/driver-uapi.rst
>>> @@ -6,3 +6,11 @@ drm/i915 uAPI
>>>   =============
>>>     .. kernel-doc:: include/uapi/drm/i915_drm.h
>>> +
>>> +drm/nouveau uAPI
>>> +================
>>> +
>>> +VM_BIND / EXEC uAPI
>>> +-------------------
>>> +
>>> +.. kernel-doc:: include/uapi/drm/nouveau_drm.h
>>> diff --git a/include/uapi/drm/nouveau_drm.h 
>>> b/include/uapi/drm/nouveau_drm.h
>>> index 853a327433d3..f6e7d40201d4 100644
>>> --- a/include/uapi/drm/nouveau_drm.h
>>> +++ b/include/uapi/drm/nouveau_drm.h
>>> @@ -126,6 +126,216 @@ struct drm_nouveau_gem_cpu_fini {
>>>       __u32 handle;
>>>   };
>>>   +/**
>>> + * struct drm_nouveau_sync - sync object
>>> + *
>>> + * This structure serves as synchronization mechanism for 
>>> (potentially)
>>> + * asynchronous operations such as EXEC or VM_BIND.
>>> + */
>>> +struct drm_nouveau_sync {
>>> +    /**
>>> +     * @flags: the flags for a sync object
>>> +     *
>>> +     * The first 8 bits are used to determine the type of the sync 
>>> object.
>>> +     */
>>> +    __u32 flags;
>>> +#define DRM_NOUVEAU_SYNC_SYNCOBJ 0x0
>>> +#define DRM_NOUVEAU_SYNC_TIMELINE_SYNCOBJ 0x1
>>> +#define DRM_NOUVEAU_SYNC_TYPE_MASK 0xf
>>> +    /**
>>> +     * @handle: the handle of the sync object
>>> +     */
>>> +    __u32 handle;
>>> +    /**
>>> +     * @timeline_value:
>>> +     *
>>> +     * The timeline point of the sync object in case the syncobj is of
>>> +     * type DRM_NOUVEAU_SYNC_TIMELINE_SYNCOBJ.
>>> +     */
>>> +    __u64 timeline_value;
>>> +};
>>> +
>>> +/**
>>> + * struct drm_nouveau_vm_init - GPU VA space init structure
>>> + *
>>> + * Used to initialize the GPU's VA space for a user client, telling 
>>> the kernel
>>> + * which portion of the VA space is managed by the UMD and kernel 
>>> respectively.
>>> + */
>>> +struct drm_nouveau_vm_init {
>>> +    /**
>>> +     * @unmanaged_addr: start address of the kernel managed VA 
>>> space region
>>> +     */
>>> +    __u64 unmanaged_addr;
>>> +    /**
>>> +     * @unmanaged_size: size of the kernel managed VA space region 
>>> in bytes
>>> +     */
>>> +    __u64 unmanaged_size;
>>> +};
>>> +
>>> +/**
>>> + * struct drm_nouveau_vm_bind_op - VM_BIND operation
>>> + *
>>> + * This structure represents a single VM_BIND operation. UMDs 
>>> should pass
>>> + * an array of this structure via struct drm_nouveau_vm_bind's 
>>> &op_ptr field.
>>> + */
>>> +struct drm_nouveau_vm_bind_op {
>>> +    /**
>>> +     * @op: the operation type
>>> +     */
>>> +    __u32 op;
>>> +/**
>>> + * @DRM_NOUVEAU_VM_BIND_OP_ALLOC:
>>> + *
>>> + * The alloc operation is used to reserve a VA space region within 
>>> the GPU's VA
>>> + * space. Optionally, the &DRM_NOUVEAU_VM_BIND_SPARSE flag can be 
>>> passed to
>>> + * instruct the kernel to create sparse mappings for the given region.
>>> + */
>>> +#define DRM_NOUVEAU_VM_BIND_OP_ALLOC 0x0
>>
>> Do you really need this operation? We have no concept of this in Xe,
>> e.g. we can create a VM and the entire address space is managed exactly
>> the same.
>
> The idea for alloc/free is to let UMDs allocate a portion of the VA 
> space (which I call a region), basically the same thing Vulkan 
> represents with a VKBuffer.

If that's mangled into the same component/interface then I can say from 
experience that this is a pretty bad idea. We have tried something 
similar with radeon and it turned out horrible.

What you want is one component for tracking the VA allocations (drm_mm 
based) and a different component/interface for tracking the VA mappings 
(probably rb tree based).

amdgpu has even gotten so far that the VA allocations are tracked in 
libdrm in userspace.

Regards,
Christian.

>
> It serves two purposes:
>
> 1. It gives the kernel (in particular the GPUVA manager) the bounds in 
> which it is allowed to merge mappings. E.g. when a user request asks 
> for a new mapping and we detect we could merge this mapping with an 
> existing one (used in another VKBuffer than the mapping request came 
> for) the driver is not allowed to change the page table for the 
> existing mapping we want to merge with (assuming that some drivers 
> would need to do this in order to merge), because the existing mapping 
> could already be in use and by re-mapping it we'd potentially cause a 
> fault on the GPU.
>
> 2. It is used for sparse residency in a way that such an allocated VA 
> space region can be flagged as sparse, such that the kernel always 
> keeps sparse mappings around for the parts of the region that do not 
> contain actual memory backed mappings.
>
> If for your driver merging is always OK, creating a single huge region 
> would do the trick I guess. Otherwise, we could also add an option to 
> the GPUVA manager (or a specific region, which could also be a single 
> huge one) within which it never merges.
>
>>
>> If this can be removed then the entire concept of regions in the GPUVA
>> can be removed too (drop struct drm_gpuva_region). I say this because
>> in Xe as I'm porting over to GPUVA the first thing I'm doing after
>> drm_gpuva_manager_init is calling drm_gpuva_region_insert on the entire
>> address space. To me this seems kinda useless but maybe I'm missing why
>> you need this for Nouveau.
>>
>> Matt
>>
>>> +/**
>>> + * @DRM_NOUVEAU_VM_BIND_OP_FREE: Free a reserved VA space region.
>>> + */
>>> +#define DRM_NOUVEAU_VM_BIND_OP_FREE 0x1
>>> +/**
>>> + * @DRM_NOUVEAU_VM_BIND_OP_MAP:
>>> + *
>>> + * Map a GEM object to the GPU's VA space. The mapping must be 
>>> fully enclosed by
>>> + * a previously allocated VA space region. If the region is sparse, 
>>> existing
>>> + * sparse mappings are overwritten.
>>> + */
>>> +#define DRM_NOUVEAU_VM_BIND_OP_MAP 0x2
>>> +/**
>>> + * @DRM_NOUVEAU_VM_BIND_OP_UNMAP:
>>> + *
>>> + * Unmap an existing mapping in the GPU's VA space. If the region 
>>> the mapping
>>> + * is located in is a sparse region, new sparse mappings are 
>>> created where the
>>> + * unmapped (memory backed) mapping was mapped previously.
>>> + */
>>> +#define DRM_NOUVEAU_VM_BIND_OP_UNMAP 0x3
>>> +    /**
>>> +     * @flags: the flags for a &drm_nouveau_vm_bind_op
>>> +     */
>>> +    __u32 flags;
>>> +/**
>>> + * @DRM_NOUVEAU_VM_BIND_SPARSE:
>>> + *
>>> + * Indicates that an allocated VA space region should be sparse.
>>> + */
>>> +#define DRM_NOUVEAU_VM_BIND_SPARSE (1 << 8)
>>> +    /**
>>> +     * @handle: the handle of the DRM GEM object to map
>>> +     */
>>> +    __u32 handle;
>>> +    /**
>>> +     * @addr:
>>> +     *
>>> +     * the address the VA space region or (memory backed) mapping 
>>> should be mapped to
>>> +     */
>>> +    __u64 addr;
>>> +    /**
>>> +     * @bo_offset: the offset within the BO backing the mapping
>>> +     */
>>> +    __u64 bo_offset;
>>> +    /**
>>> +     * @range: the size of the requested mapping in bytes
>>> +     */
>>> +    __u64 range;
>>> +};
>>> +
>>> +/**
>>> + * struct drm_nouveau_vm_bind - structure for 
>>> DRM_IOCTL_NOUVEAU_VM_BIND
>>> + */
>>> +struct drm_nouveau_vm_bind {
>>> +    /**
>>> +     * @op_count: the number of &drm_nouveau_vm_bind_op
>>> +     */
>>> +    __u32 op_count;
>>> +    /**
>>> +     * @flags: the flags for a &drm_nouveau_vm_bind ioctl
>>> +     */
>>> +    __u32 flags;
>>> +/**
>>> + * @DRM_NOUVEAU_VM_BIND_RUN_ASYNC:
>>> + *
>>> + * Indicates that the given VM_BIND operation should be executed 
>>> asynchronously
>>> + * by the kernel.
>>> + *
>>> + * If this flag is not supplied the kernel executes the associated 
>>> operations
>>> + * synchronously and doesn't accept any &drm_nouveau_sync objects.
>>> + */
>>> +#define DRM_NOUVEAU_VM_BIND_RUN_ASYNC 0x1
>>> +    /**
>>> +     * @wait_count: the number of wait &drm_nouveau_syncs
>>> +     */
>>> +    __u32 wait_count;
>>> +    /**
>>> +     * @sig_count: the number of &drm_nouveau_syncs to signal when 
>>> finished
>>> +     */
>>> +    __u32 sig_count;
>>> +    /**
>>> +     * @wait_ptr: pointer to &drm_nouveau_syncs to wait for
>>> +     */
>>> +    __u64 wait_ptr;
>>> +    /**
>>> +     * @sig_ptr: pointer to &drm_nouveau_syncs to signal when finished
>>> +     */
>>> +    __u64 sig_ptr;
>>> +    /**
>>> +     * @op_ptr: pointer to the &drm_nouveau_vm_bind_ops to execute
>>> +     */
>>> +    __u64 op_ptr;
>>> +};
>>> +
>>> +/**
>>> + * struct drm_nouveau_exec_push - EXEC push operation
>>> + *
>>> + * This structure represents a single EXEC push operation. UMDs 
>>> should pass an
>>> + * array of this structure via struct drm_nouveau_exec's &push_ptr 
>>> field.
>>> + */
>>> +struct drm_nouveau_exec_push {
>>> +    /**
>>> +     * @va: the virtual address of the push buffer mapping
>>> +     */
>>> +    __u64 va;
>>> +    /**
>>> +     * @va_len: the length of the push buffer mapping
>>> +     */
>>> +    __u64 va_len;
>>> +};
>>> +
>>> +/**
>>> + * struct drm_nouveau_exec - structure for DRM_IOCTL_NOUVEAU_EXEC
>>> + */
>>> +struct drm_nouveau_exec {
>>> +    /**
>>> +     * @channel: the channel to execute the push buffer in
>>> +     */
>>> +    __u32 channel;
>>> +    /**
>>> +     * @push_count: the number of &drm_nouveau_exec_push ops
>>> +     */
>>> +    __u32 push_count;
>>> +    /**
>>> +     * @wait_count: the number of wait &drm_nouveau_syncs
>>> +     */
>>> +    __u32 wait_count;
>>> +    /**
>>> +     * @sig_count: the number of &drm_nouveau_syncs to signal when 
>>> finished
>>> +     */
>>> +    __u32 sig_count;
>>> +    /**
>>> +     * @wait_ptr: pointer to &drm_nouveau_syncs to wait for
>>> +     */
>>> +    __u64 wait_ptr;
>>> +    /**
>>> +     * @sig_ptr: pointer to &drm_nouveau_syncs to signal when finished
>>> +     */
>>> +    __u64 sig_ptr;
>>> +    /**
>>> +     * @push_ptr: pointer to &drm_nouveau_exec_push ops
>>> +     */
>>> +    __u64 push_ptr;
>>> +};
>>> +
>>>   #define DRM_NOUVEAU_GETPARAM           0x00 /* deprecated */
>>>   #define DRM_NOUVEAU_SETPARAM           0x01 /* deprecated */
>>>   #define DRM_NOUVEAU_CHANNEL_ALLOC      0x02 /* deprecated */
>>> @@ -136,6 +346,9 @@ struct drm_nouveau_gem_cpu_fini {
>>>   #define DRM_NOUVEAU_NVIF               0x07
>>>   #define DRM_NOUVEAU_SVM_INIT           0x08
>>>   #define DRM_NOUVEAU_SVM_BIND           0x09
>>> +#define DRM_NOUVEAU_VM_INIT            0x10
>>> +#define DRM_NOUVEAU_VM_BIND            0x11
>>> +#define DRM_NOUVEAU_EXEC               0x12
>>>   #define DRM_NOUVEAU_GEM_NEW            0x40
>>>   #define DRM_NOUVEAU_GEM_PUSHBUF        0x41
>>>   #define DRM_NOUVEAU_GEM_CPU_PREP       0x42
>>> @@ -197,6 +410,9 @@ struct drm_nouveau_svm_bind {
>>>   #define DRM_IOCTL_NOUVEAU_GEM_CPU_FINI       DRM_IOW 
>>> (DRM_COMMAND_BASE + DRM_NOUVEAU_GEM_CPU_FINI, struct 
>>> drm_nouveau_gem_cpu_fini)
>>>   #define DRM_IOCTL_NOUVEAU_GEM_INFO DRM_IOWR(DRM_COMMAND_BASE + 
>>> DRM_NOUVEAU_GEM_INFO, struct drm_nouveau_gem_info)
>>>   +#define DRM_IOCTL_NOUVEAU_VM_INIT DRM_IOWR(DRM_COMMAND_BASE + 
>>> DRM_NOUVEAU_VM_INIT, struct drm_nouveau_vm_init)
>>> +#define DRM_IOCTL_NOUVEAU_VM_BIND DRM_IOWR(DRM_COMMAND_BASE + 
>>> DRM_NOUVEAU_VM_BIND, struct drm_nouveau_vm_bind)
>>> +#define DRM_IOCTL_NOUVEAU_EXEC DRM_IOWR(DRM_COMMAND_BASE + 
>>> DRM_NOUVEAU_EXEC, struct drm_nouveau_exec)
>>>   #if defined(__cplusplus)
>>>   }
>>>   #endif
>>> -- 
>>> 2.39.0
>>>
>>
>

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