From patchwork Wed Jan 29 19:52:12 2025 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Matthew Brost X-Patchwork-Id: 13954071 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 EBB63C0219A for ; Wed, 29 Jan 2025 19:51:51 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 9366110E8C0; Wed, 29 Jan 2025 19:51:30 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; unprotected) header.d=intel.com header.i=@intel.com header.b="SxvSRfRF"; dkim-atps=neutral Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.10]) by gabe.freedesktop.org (Postfix) with ESMTPS id 3989010E8AC; Wed, 29 Jan 2025 19:51:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1738180287; x=1769716287; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=udAYvU6NHprmQPlHjKE6UqgqDIF3Y3IPLbRor61gWQQ=; b=SxvSRfRFDtn5POmDzTRuXJVOvwjohJP0gSO9LCHqtc/J2mrZPvLB9zKo KB2FJxxldDEFMbtbYj4HOuOuJJgj1m+cBnMj2aLMuiopj8LLsZBpxVxfo IZqsW/Oa2WrRjxD3JComD++P4w+UqwJDdIMMxgR4wc9VxnhEQ3uDt17cg W5TbTz3paV5Q+wRUbT+fZNB4t9oYfImi/iRPuQef5OmOuyfwMNtzdmEY+ /lnW5xlXEMjcSzVvPY0yQNSCKWl+/5x74PZlKBJCWUBAkWTy/Hnq0Aarz SpiEKPXMErzmIprrK6DI65fJR0NmkWLDJp9drVNFXiM8ZbnAvDmzy+BcB g==; X-CSE-ConnectionGUID: ZmtszIEHRPSOBLwt/hsjQQ== X-CSE-MsgGUID: 0+kI+wNSQ2GdP2XwfehV7w== X-IronPort-AV: E=McAfee;i="6700,10204,11314"; a="50132910" X-IronPort-AV: E=Sophos;i="6.12,310,1728975600"; d="scan'208";a="50132910" Received: from fmviesa002.fm.intel.com ([10.60.135.142]) by fmvoesa104.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 29 Jan 2025 11:51:27 -0800 X-CSE-ConnectionGUID: KM2MNz8lSkOIcmMGD17oyA== X-CSE-MsgGUID: oSJ0j8v1SviG+g0/DsUbaw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.12,224,1728975600"; d="scan'208";a="132392211" Received: from lstrano-desk.jf.intel.com ([10.54.39.91]) by fmviesa002-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 29 Jan 2025 11:51:27 -0800 From: Matthew Brost To: intel-xe@lists.freedesktop.org, dri-devel@lists.freedesktop.org Cc: himal.prasad.ghimiray@intel.com, apopple@nvidia.com, airlied@gmail.com, thomas.hellstrom@linux.intel.com, simona.vetter@ffwll.ch, felix.kuehling@amd.com, dakr@kernel.org Subject: [PATCH v4 33/33] drm/doc: gpusvm: Add GPU SVM documentation Date: Wed, 29 Jan 2025 11:52:12 -0800 Message-Id: <20250129195212.745731-34-matthew.brost@intel.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20250129195212.745731-1-matthew.brost@intel.com> References: <20250129195212.745731-1-matthew.brost@intel.com> MIME-Version: 1.0 X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" Add documentation for agree upon GPU SVM design principles, current status, and future plans. v4: - Address Thomas's feedback Signed-off-by: Matthew Brost Reviewed-by: Thomas Hellström --- Documentation/gpu/rfc/gpusvm.rst | 84 ++++++++++++++++++++++++++++++++ Documentation/gpu/rfc/index.rst | 4 ++ 2 files changed, 88 insertions(+) create mode 100644 Documentation/gpu/rfc/gpusvm.rst diff --git a/Documentation/gpu/rfc/gpusvm.rst b/Documentation/gpu/rfc/gpusvm.rst new file mode 100644 index 000000000000..2d88f5981981 --- /dev/null +++ b/Documentation/gpu/rfc/gpusvm.rst @@ -0,0 +1,84 @@ +=============== +GPU SVM Section +=============== + +Agreed upon design principles +============================= + +* migrate_to_ram path + * Rely only on core MM concepts (migration PTEs, page references, and + page locking). The reasoning is that this is not required, can lead to + livelock cases, and is generally not a good idea to seal races using + driver-invented locks. + * No driver specific locks other than locks for hardware interaction in + this path. + * Partial migration is supported (i.e., a subset of pages attempting to + migrate can actually migrate, with only the faulting page guaranteed + to migrate). + * Driver handles mixed migrations via retry loops rather than locking. +* Eviction + * Only looking at physical memory data structures and locks as opposed to + looking at virtual memory data structures and locks. + * No looking at mm/vma structs or relying on those being locked. +* GPU fault side + * mmap_read only used around core MM functions which require this lock + and should strive to take mmap_read lock only in GPU SVM layer. + * Big retry loop to handle all races with the mmu notifier under the gpu + pagetable locks/mmu notifier range lock/whatever we end up calling + those. + * Races (especially against concurrent eviction or migrate_to_ram) + should not be handled on the fault side by trying to hold locks; + rather, they should be handled using retry loops. One possible + exception is holding a BO's dma-resv lock during the initial migration + to VRAM, as this is a well-defined lock that can be taken underneath + the mmap_read lock. +* Physical memory to virtual backpointer + * Does not work, no pointers from physical memory to virtual should + exist. + * Physical memory backpointer (page->zone_device_data) should be stable + from allocation to page free. +* GPU pagetable locking + * Notifier lock only protects range tree, pages valid state for a range + (rather than seqno due to wider notifiers), pagetable entries, and + mmu notifier seqno tracking, it is not a global lock to protect + against races. + * All races handled with big retry as mentioned above. + +Overview of current design +========================== + +Current design is simple as possible to get a working basline in which can be +built upon. + +.. kernel-doc:: drivers/gpu/drm/xe/drm_gpusvm.c + :doc: Overview + :doc: Locking + :doc: Migrataion + :doc: Partial Unmapping of Ranges + :doc: Examples + +Possible future design features +=============================== + +* Concurrent GPU faults + * CPU faults are concurrent so makes sense to have concurrent GPU + faults. + * Should be possible with fined grained locking in the driver GPU + fault handler. + * No expected GPU SVM changes required. +* Ranges with mixed system and device pages + * Can be added if required to drm_gpusvm_get_pages fairly easily. +* Multi-GPU support + * Work in progress and patches expected after initially landing on GPU + SVM. + * Ideally can be done with little to no changes to GPU SVM. +* Drop ranges in favor of radix tree + * May be desirable for faster notifiers. +* Compound device pages + * Nvidia, AMD, and Intel all have agreed expensive core MM functions in + migrate device layer are a performance bottleneck, having compound + device pages should help increase performance by reducing the number + of these expensive calls. +* Higher order dma mapping for migration + * 4k dma mapping adversely affects migration performance on Intel + hardware, higher order (2M) dma mapping should help here. diff --git a/Documentation/gpu/rfc/index.rst b/Documentation/gpu/rfc/index.rst index 476719771eef..396e535377fb 100644 --- a/Documentation/gpu/rfc/index.rst +++ b/Documentation/gpu/rfc/index.rst @@ -16,6 +16,10 @@ host such documentation: * Once the code has landed move all the documentation to the right places in the main core, helper or driver sections. +.. toctree:: + + gpusvm.rst + .. toctree:: i915_gem_lmem.rst