From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id D6676C433F5 for ; Thu, 28 Apr 2022 08:55:39 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 82A3710F934; Thu, 28 Apr 2022 08:55:38 +0000 (UTC) Received: from mga05.intel.com (mga05.intel.com [192.55.52.43]) by gabe.freedesktop.org (Postfix) with ESMTPS id 8663610F935; Thu, 28 Apr 2022 08:55:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1651136137; x=1682672137; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=Fpw0i6xvUgZW/GN6YtXTzbX90L63ikbeS0tvGH1O6lk=; b=HDJ9+4jTaYtBrwDOqLE7ptazVOYmq+Mn9lC2HYdiazixYD271uB6/REA 7ektZK2bSJ2wHi/AH23SwAS4LrAoAiPfV56p3IHWOR9C0t0mb6Ud17UPq MhQfdN0jPsN/cyKmYrEk34GD5AHfdNXw8OySDRjE6gN7xFt5h0VlR0x51 OwyblQ6c1ObMw1r6iMrHpAELU/P4KtzaYkkYzsmVoPctdeSCQuDalJudE bzmc7vRtu3EQ3FOFn7uNeiRgloSfEAkW5hSQuZeERrt0opDl4YLCtLh/i pi9KSLR40u40AD8/dFqRk+dIvmFb1luNseRFrBoa2ior9dfBGuT12BfRH A==; X-IronPort-AV: E=McAfee;i="6400,9594,10330"; a="352647379" X-IronPort-AV: E=Sophos;i="5.90,295,1643702400"; d="scan'208";a="352647379" Received: from orsmga003.jf.intel.com ([10.7.209.27]) by fmsmga105.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 28 Apr 2022 01:55:14 -0700 X-IronPort-AV: E=Sophos;i="5.90,295,1643702400"; d="scan'208";a="514166917" Received: from wdries-mobl1.ger.corp.intel.com (HELO [10.213.210.166]) ([10.213.210.166]) by orsmga003-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 28 Apr 2022 01:55:12 -0700 Message-ID: Date: Thu, 28 Apr 2022 09:55:10 +0100 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: Matthew Auld , intel-gfx@lists.freedesktop.org References: <20220420171328.57253-1-matthew.auld@intel.com> <896cba53-4c94-6de2-e8a3-ace648386576@intel.com> From: Tvrtko Ursulin Organization: Intel Corporation UK Plc In-Reply-To: <896cba53-4c94-6de2-e8a3-ace648386576@intel.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit 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?= , Kenneth Graunke , mesa-dev@lists.freedesktop.org, dri-devel@lists.freedesktop.org, Daniel Vetter Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" On 27/04/2022 18:36, Matthew Auld wrote: > On 27/04/2022 09:36, Tvrtko Ursulin wrote: >> >> On 20/04/2022 18:13, 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; >> >> Would unallocated_cpu_visible_size be useful, to follow the total >> unallocated_size? > > Make sense. But I don't think unallocated_size has actually been > properly wired up yet. It still just gives the same value as > probed_size. IIRC for unallocated_size we still need a real > user/usecase/umd, before wiring that up for real with the existing avail > tracking. Once we have that we can also add unallocated_cpu_visible_size. So this does nothing at the moment: info.unallocated_size = mr->avail; Right, it is set to "mem->avail = mem->total;" at region init time and I indeed can't find it ever getting modified. Okay. >> Btw, have we ever considered whether unallocated_size should require >> CAP_SYS_ADMIN/PERFMON or something? > > Note sure. But just in case we do add it for real at some point, why the > added restriction? To avoid a side channel, albeit perhaps a very weak one. For engine utilization we require CAP_SYS_PERFMON, but that is implied by the perf core API. It's open for discussion. I guess it may make sense to limit it also because it is questionable the field(s) are even useful. > >> >>> +        }; >>> +    }; >>> +}; >>> + >>> +/** >>> + * 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), likefor 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 tosystem 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. >>> +     */ >> >> So "needs_cpu_access" flag could almost be viewed as a sub-region >> placement priority? What I mean is this: >> >> 1) >> placements=device,system flags= >> >> This results in placement priorities: device, device_cpu_mappable, >> system. > > Yup. > >> >> 2) >> placements=device,system flags=needs_cpu_access >> >> This results in placement priorities: device_cpu_mappable, device, >> system. > > Here it would only be: device_cpu_mappable, system. We would completely > ignore "device" in this case. > >> >> Is this correct? >> >> The benefit of the flag is that i915 can place the object to the right >> place from the start instead of on the first CPU access? Is that worth >> it or is there more to it? > > Yeah, the object will only be placed somewhere that is also CPU > mappable, with the flag set. Hm, wouldn't it be more efficient to be able to migrate it over to non-mappable in cases when mappable is over-subscribed? >>> +#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 usagesee >>> +     * 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 noneed 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 thegiven vma. >>> +     * >>> +     * Possible values: >>> +     * >>> +     * DRM_I915_QUERY_VMA_INFO_CPU_VISIBLE - Set ifthe pages backing >>> the >>> +     * vma are currently CPU accessible. If this isnot set then the >>> vma is >>> +     * currently backed by I915_MEMORY_CLASS_DEVICEmemory, which the >>> CPU >>> +     * cannot directly access(this is only possibleon 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. >> >> I think there should be justification for the new query documented as >> well. (Why on top of what.) > > Yeah, I'm wondering now if we can just drop this part of the uapi, for > now at least, and focus on landing the new flag stuff first. > >> >> Without it personally I can't immediately understand why the >> disconnect between the object based and VMA based API. Userspace has >> to do some intervening operations like either execbuf, or vm bind in >> the future, to make this query usable after object creation. So >> question is why wouldn't it know already which placements it allowed >> and so would i915 auto-migrate or not for this particular object. No? >> Or in other words why this wouldn't be an object based query since the >> question it is answering is about the object backing store and not the >> VMA. > > Yeah, just using the object handle or so I guess would also work. Thanks > for the comments. I saw other folks have said the same so omitting for now sounds good to me indeed. Regards, Tvrtko