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[87.176.185.225]) by smtp.gmail.com with ESMTPSA id b8-20020a056402278800b004261ac0126asm101716ede.94.2022.04.26.23.55.08 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 26 Apr 2022 23:55:08 -0700 (PDT) Message-ID: Date: Wed, 27 Apr 2022 08:55:07 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.7.0 Content-Language: en-US To: Lionel Landwerlin , Matthew Auld , intel-gfx@lists.freedesktop.org References: <20220420171328.57253-1-matthew.auld@intel.com> <5553382d-2674-76f0-ab6e-408b99111a62@intel.com> From: =?UTF-8?Q?Christian_K=c3=b6nig?= In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Mailman-Approved-At: Thu, 28 Apr 2022 08:39:08 +0000 Subject: Re: [Intel-gfx] [PATCH v2] drm/doc: add rfc section for small BAR uapi X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: =?UTF-8?Q?Thomas_Hellstr=c3=b6m?= , Daniel Vetter , dri-devel@lists.freedesktop.org, Kenneth Graunke , mesa-dev@lists.freedesktop.org Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" Well usually we increment the drm minor version when adding some new flags on amdgpu. Additional to that just one comment from our experience with that: You don't just need one flag, but two. The first one is a hint which says "CPU access needed" and the second is a promise which says "CPU access never needed". The background is that on a whole bunch of buffers you can 100% certain say that you will never ever need CPU access. Then at least we have a whole bunch of buffers where we might need CPU access, but can't tell for sure. And last we have stuff like transfer buffers you can be 100% sure that you need CPU access. Separating it like this helped a lot with performance on small BAR systems. Regards, Christian. Am 27.04.22 um 08:48 schrieb Lionel Landwerlin: > One question though, how do we detect that this flag > (I915_GEM_CREATE_EXT_FLAG_NEEDS_CPU_ACCESS) is accepted on a given > kernel? > I assume older kernels are going to reject object creation if we use > this flag? > > I didn't plan to use __drm_i915_query_vma_info, but isn't it > inconsistent to select the placement on the GEM object and then query > whether it's mappable by address? > You made a comment stating this is racy, wouldn't querying on the GEM > object prevent this? > > Thanks, > > -Lionel > > On 27/04/2022 09:35, Lionel Landwerlin wrote: >> Hi Matt, >> >> >> The proposal looks good to me. >> >> Looking forward to try it on drm-tip. >> >> >> -Lionel >> >> On 20/04/2022 20:13, Matthew Auld wrote: >>> Add an entry for the new uapi needed for small BAR on DG2+. >>> >>> v2: >>>    - Some spelling fixes and other small tweaks. (Akeem & Thomas) >>>    - Rework error capture interactions, including no longer needing >>>      NEEDS_CPU_ACCESS for objects marked for capture. (Thomas) >>>    - Add probed_cpu_visible_size. (Lionel) >>> >>> Signed-off-by: Matthew Auld >>> Cc: Thomas Hellström >>> Cc: Lionel Landwerlin >>> Cc: Jon Bloomfield >>> Cc: Daniel Vetter >>> Cc: Jordan Justen >>> Cc: Kenneth Graunke >>> Cc: Akeem G Abodunrin >>> Cc: mesa-dev@lists.freedesktop.org >>> --- >>>   Documentation/gpu/rfc/i915_small_bar.h   | 190 >>> +++++++++++++++++++++++ >>>   Documentation/gpu/rfc/i915_small_bar.rst |  58 +++++++ >>>   Documentation/gpu/rfc/index.rst          |   4 + >>>   3 files changed, 252 insertions(+) >>>   create mode 100644 Documentation/gpu/rfc/i915_small_bar.h >>>   create mode 100644 Documentation/gpu/rfc/i915_small_bar.rst >>> >>> diff --git a/Documentation/gpu/rfc/i915_small_bar.h >>> b/Documentation/gpu/rfc/i915_small_bar.h >>> new file mode 100644 >>> index 000000000000..7bfd0cf44d35 >>> --- /dev/null >>> +++ b/Documentation/gpu/rfc/i915_small_bar.h >>> @@ -0,0 +1,190 @@ >>> +/** >>> + * struct __drm_i915_memory_region_info - Describes one region as >>> known to the >>> + * driver. >>> + * >>> + * Note this is using both struct drm_i915_query_item and struct >>> drm_i915_query. >>> + * For this new query we are adding the new query id >>> DRM_I915_QUERY_MEMORY_REGIONS >>> + * at &drm_i915_query_item.query_id. >>> + */ >>> +struct __drm_i915_memory_region_info { >>> +    /** @region: The class:instance pair encoding */ >>> +    struct drm_i915_gem_memory_class_instance region; >>> + >>> +    /** @rsvd0: MBZ */ >>> +    __u32 rsvd0; >>> + >>> +    /** @probed_size: Memory probed by the driver (-1 = unknown) */ >>> +    __u64 probed_size; >>> + >>> +    /** @unallocated_size: Estimate of memory remaining (-1 = >>> unknown) */ >>> +    __u64 unallocated_size; >>> + >>> +    union { >>> +        /** @rsvd1: MBZ */ >>> +        __u64 rsvd1[8]; >>> +        struct { >>> +            /** >>> +             * @probed_cpu_visible_size: Memory probed by the driver >>> +             * that is CPU accessible. (-1 = unknown). >>> +             * >>> +             * This will be always be <= @probed_size, and the >>> +             * remainder(if there is any) will not be CPU >>> +             * accessible. >>> +             */ >>> +            __u64 probed_cpu_visible_size; >>> +        }; >>> +    }; >>> +}; >>> + >>> +/** >>> + * struct __drm_i915_gem_create_ext - Existing gem_create >>> behaviour, with added >>> + * extension support using struct i915_user_extension. >>> + * >>> + * Note that new buffer flags should be added here, at least for >>> the stuff that >>> + * is immutable. Previously we would have two ioctls, one to create >>> the object >>> + * with gem_create, and another to apply various parameters, >>> however this >>> + * creates some ambiguity for the params which are considered >>> immutable. Also in >>> + * general we're phasing out the various SET/GET ioctls. >>> + */ >>> +struct __drm_i915_gem_create_ext { >>> +    /** >>> +     * @size: Requested size for the object. >>> +     * >>> +     * The (page-aligned) allocated size for the object will be >>> returned. >>> +     * >>> +     * Note that for some devices we have might have further minimum >>> +     * page-size restrictions(larger than 4K), like for device >>> local-memory. >>> +     * However in general the final size here should always reflect >>> any >>> +     * rounding up, if for example using the >>> I915_GEM_CREATE_EXT_MEMORY_REGIONS >>> +     * extension to place the object in device local-memory. >>> +     */ >>> +    __u64 size; >>> +    /** >>> +     * @handle: Returned handle for the object. >>> +     * >>> +     * Object handles are nonzero. >>> +     */ >>> +    __u32 handle; >>> +    /** >>> +     * @flags: Optional flags. >>> +     * >>> +     * Supported values: >>> +     * >>> +     * I915_GEM_CREATE_EXT_FLAG_NEEDS_CPU_ACCESS - Signal to the >>> kernel that >>> +     * the object will need to be accessed via the CPU. >>> +     * >>> +     * Only valid when placing objects in I915_MEMORY_CLASS_DEVICE, >>> and >>> +     * only strictly required on platforms where only some of the >>> device >>> +     * memory is directly visible or mappable through the CPU, like >>> on DG2+. >>> +     * >>> +     * One of the placements MUST also be I915_MEMORY_CLASS_SYSTEM, to >>> +     * ensure we can always spill the allocation to system memory, >>> if we >>> +     * can't place the object in the mappable part of >>> +     * I915_MEMORY_CLASS_DEVICE. >>> +     * >>> +     * Note that since the kernel only supports flat-CCS on objects >>> that can >>> +     * *only* be placed in I915_MEMORY_CLASS_DEVICE, we therefore >>> don't >>> +     * support I915_GEM_CREATE_EXT_FLAG_NEEDS_CPU_ACCESS together with >>> +     * flat-CCS. >>> +     * >>> +     * Without this hint, the kernel will assume that non-mappable >>> +     * I915_MEMORY_CLASS_DEVICE is preferred for this object. Note >>> that the >>> +     * kernel can still migrate the object to the mappable part, as >>> a last >>> +     * resort, if userspace ever CPU faults this object, but this >>> might be >>> +     * expensive, and so ideally should be avoided. >>> +     */ >>> +#define I915_GEM_CREATE_EXT_FLAG_NEEDS_CPU_ACCESS (1 << 0) >>> +    __u32 flags; >>> +    /** >>> +     * @extensions: The chain of extensions to apply to this object. >>> +     * >>> +     * This will be useful in the future when we need to support >>> several >>> +     * different extensions, and we need to apply more than one when >>> +     * creating the object. See struct i915_user_extension. >>> +     * >>> +     * If we don't supply any extensions then we get the same old >>> gem_create >>> +     * behaviour. >>> +     * >>> +     * For I915_GEM_CREATE_EXT_MEMORY_REGIONS usage see >>> +     * struct drm_i915_gem_create_ext_memory_regions. >>> +     * >>> +     * For I915_GEM_CREATE_EXT_PROTECTED_CONTENT usage see >>> +     * struct drm_i915_gem_create_ext_protected_content. >>> +     */ >>> +#define I915_GEM_CREATE_EXT_MEMORY_REGIONS 0 >>> +#define I915_GEM_CREATE_EXT_PROTECTED_CONTENT 1 >>> +    __u64 extensions; >>> +}; >>> + >>> +#define DRM_I915_QUERY_VMA_INFO    5 >>> + >>> +/** >>> + * struct __drm_i915_query_vma_info >>> + * >>> + * Given a vm and GTT address, lookup the corresponding vma, >>> returning its set >>> + * of attributes. >>> + * >>> + * .. code-block:: C >>> + * >>> + *    struct drm_i915_query_vma_info info = {}; >>> + *    struct drm_i915_query_item item = { >>> + *        .data_ptr = (uintptr_t)&info, >>> + *        .query_id = DRM_I915_QUERY_VMA_INFO, >>> + *    }; >>> + *    struct drm_i915_query query = { >>> + *        .num_items = 1, >>> + *        .items_ptr = (uintptr_t)&item, >>> + *    }; >>> + *    int err; >>> + * >>> + *    // Unlike some other types of queries, there is no need to >>> first query >>> + *    // the size of the data_ptr blob here, since we already know >>> ahead of >>> + *    // time how big this needs to be. >>> + *    item.length = sizeof(info); >>> + * >>> + *    // Next we fill in the vm_id and ppGTT address of the vma we >>> wish >>> + *    // to query, before then firing off the query. >>> + *    info.vm_id = vm_id; >>> + *    info.offset = gtt_address; >>> + *    err = ioctl(fd, DRM_IOCTL_I915_QUERY, &query); >>> + *    if (err || item.length < 0) ... >>> + * >>> + *    // If all went well we can now inspect the returned attributes. >>> + *    if (info.attributes & DRM_I915_QUERY_VMA_INFO_CPU_VISIBLE) ... >>> + */ >>> +struct __drm_i915_query_vma_info { >>> +    /** >>> +     * @vm_id: The given vm id that contains the vma. The id is the >>> value >>> +     * returned by the DRM_I915_GEM_VM_CREATE. See struct >>> +     * drm_i915_gem_vm_control.vm_id. >>> +     */ >>> +    __u32 vm_id; >>> +    /** @pad: MBZ. */ >>> +    __u32 pad; >>> +    /** >>> +     * @offset: The corresponding ppGTT address of the vma which >>> the kernel >>> +     * will use to perform the lookup. >>> +     */ >>> +    __u64 offset; >>> +    /** >>> +     * @attributes: The returned attributes for the given vma. >>> +     * >>> +     * Possible values: >>> +     * >>> +     * DRM_I915_QUERY_VMA_INFO_CPU_VISIBLE - Set if the pages >>> backing the >>> +     * vma are currently CPU accessible. If this is not set then >>> the vma is >>> +     * currently backed by I915_MEMORY_CLASS_DEVICE memory, which >>> the CPU >>> +     * cannot directly access(this is only possible on discrete >>> devices with >>> +     * a small BAR). Attempting to MMAP and fault such an object will >>> +     * require the kernel first synchronising any GPU work tied to the >>> +     * object, before then migrating the pages, either to the CPU >>> accessible >>> +     * part of I915_MEMORY_CLASS_DEVICE, or >>> I915_MEMORY_CLASS_SYSTEM, if the >>> +     * placements permit it. See >>> I915_GEM_CREATE_EXT_FLAG_NEEDS_CPU_ACCESS. >>> +     * >>> +     * Note that this is inherently racy. >>> +     */ >>> +#define DRM_I915_QUERY_VMA_INFO_CPU_VISIBLE (1<<0) >>> +    __u64 attributes; >>> +    /** @rsvd: MBZ */ >>> +    __u32 rsvd[4]; >>> +}; >>> diff --git a/Documentation/gpu/rfc/i915_small_bar.rst >>> b/Documentation/gpu/rfc/i915_small_bar.rst >>> new file mode 100644 >>> index 000000000000..be3d9bcdd86d >>> --- /dev/null >>> +++ b/Documentation/gpu/rfc/i915_small_bar.rst >>> @@ -0,0 +1,58 @@ >>> +========================== >>> +I915 Small BAR RFC Section >>> +========================== >>> +Starting from DG2 we will have resizable BAR support for device >>> local-memory(i.e >>> +I915_MEMORY_CLASS_DEVICE), but in some cases the final BAR size >>> might still be >>> +smaller than the total probed_size. In such cases, only some subset of >>> +I915_MEMORY_CLASS_DEVICE will be CPU accessible(for example the >>> first 256M), >>> +while the remainder is only accessible via the GPU. >>> + >>> +I915_GEM_CREATE_EXT_FLAG_NEEDS_CPU_ACCESS flag >>> +---------------------------------------------- >>> +New gem_create_ext flag to tell the kernel that a BO will require >>> CPU access. >>> +This becomes important when placing an object in >>> I915_MEMORY_CLASS_DEVICE, where >>> +underneath the device has a small BAR, meaning only some portion of >>> it is CPU >>> +accessible. Without this flag the kernel will assume that CPU >>> access is not >>> +required, and prioritize using the non-CPU visible portion of >>> +I915_MEMORY_CLASS_DEVICE. >>> + >>> +.. kernel-doc:: Documentation/gpu/rfc/i915_small_bar.h >>> +   :functions: __drm_i915_gem_create_ext >>> + >>> +probed_cpu_visible_size attribute >>> +--------------------------------- >>> +New struct__drm_i915_memory_region attribute which returns the >>> total size of the >>> +CPU accessible portion, for the particular region. This should only be >>> +applicable for I915_MEMORY_CLASS_DEVICE. >>> + >>> +Vulkan will need this as part of creating a separate VkMemoryHeap >>> with the >>> +VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT set, to represent the CPU >>> visible portion, >>> +where the total size of the heap needs to be known. >>> + >>> +.. kernel-doc:: Documentation/gpu/rfc/i915_small_bar.h >>> +   :functions: __drm_i915_memory_region_info >>> + >>> +DRM_I915_QUERY_VMA_INFO query >>> +----------------------------- >>> +Query the attributes of some vma. Given a vm and GTT offset, find the >>> +respective vma, and return its set of attributes. For now we only >>> support >>> +DRM_I915_QUERY_VMA_INFO_CPU_VISIBLE, which is set if the object/vma is >>> +currently placed in memory that is accessible by the CPU. This >>> should always be >>> +set on devices where the CPU probed_cpu_visible_size of >>> I915_MEMORY_CLASS_DEVICE >>> +matches the probed_size. If this is not set then CPU faulting the >>> object will >>> +likely first require migrating the pages. >>> + >>> +.. kernel-doc:: Documentation/gpu/rfc/i915_small_bar.h >>> +   :functions: __drm_i915_query_vma_info >>> + >>> +Error Capture restrictions >>> +-------------------------- >>> +With error capture we have two new restrictions: >>> + >>> +    1) Error capture is best effort on small BAR systems; if the >>> pages are not >>> +    CPU accessible, at the time of capture, then the kernel is free >>> to skip >>> +    trying to capture them. >>> + >>> +    2) On discrete we now reject error capture on recoverable >>> contexts. In the >>> +    future the kernel may want to blit during error capture, when >>> for example >>> +    something is not currently CPU accessible. >>> diff --git a/Documentation/gpu/rfc/index.rst >>> b/Documentation/gpu/rfc/index.rst >>> index 91e93a705230..5a3bd3924ba6 100644 >>> --- a/Documentation/gpu/rfc/index.rst >>> +++ b/Documentation/gpu/rfc/index.rst >>> @@ -23,3 +23,7 @@ host such documentation: >>>   .. toctree:: >>>         i915_scheduler.rst >>> + >>> +.. toctree:: >>> + >>> +    i915_small_bar.rst >> >> >