From patchwork Thu May 15 21:19:38 2025 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mario Limonciello X-Patchwork-Id: 890518 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 56FB2218AAA; Thu, 15 May 2025 21:20:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747344001; cv=none; b=m5WK2NsZZkhFqXZzeZPdCJEL0PzfAMS8425jfXIERSbC7lU8CIkkMTouvUps73TuadB9jkhHhg3DS9kBKlvGrv6CJT36tlDbrWR07uCf8ccUU4VZzhLhomf4kDKqlHTLpoO908HqnTvxUQfD4E4jgDEd5OlMNkpYn1nZ/mzASgM= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747344001; c=relaxed/simple; bh=ZZPLPFekmqonJmYX/xbKyqOt43jN+w5eM5nlYX4e6+c=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=BzcqEbcskEi6uKbRLtJIs1E5ikjXXl+RLBkbw6NLKFw95hxYMN/xspJTlAu8XlqmppAeTs8b7RHXMsOqy0u4H9Krsgp41BgQnI4fQDELcaSBt69qgLqaKnHWHm3+wFxb67bkONo9U0yldFQ4mPHDozjmafhyVKnN+vNdKWzHr6s= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=jZU4IX+7; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="jZU4IX+7" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D4233C4CEF1; Thu, 15 May 2025 21:19:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1747344000; bh=ZZPLPFekmqonJmYX/xbKyqOt43jN+w5eM5nlYX4e6+c=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=jZU4IX+7uYEM2hSyE7J+xtar0A883pyCqJrN0dlvbuCaZ8j9rEzehCtw5ayUWIubl iPHQEYJDowe0E8Emsxe61p36Cu8y6AArAJvXiEauQMB3/g0AFHbHxDE8qsLQUx1Vlf MrfnegcAPmFPoPimZkmppKz7MmswwxvsTeC0sM3X7i22ednQySMa7W7NegvBV7Ddfc +duaTlAGqfztPDHH44HSmaLMeDtjxKx1KPU+YxIsxiA6S4dkdO4/Xk0WZPUwbt63qL xNOWlAO1oOhxdxB0tjhF5/hbhWciJl8ZKyqkOq4h6GPeP626JnsF37SWKLdQ9t6+th pd2IZE1VXEjZA== From: Mario Limonciello To: =?utf-8?q?Ilpo_J=C3=A4rvinen?= Cc: Mario Limonciello , Perry Yuan , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org (maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)), "H . Peter Anvin" , Jonathan Corbet , Huang Rui , "Gautham R . Shenoy" , "Rafael J . Wysocki" , Viresh Kumar , platform-driver-x86@vger.kernel.org (open list:AMD HETERO CORE HARDWARE FEEDBACK DRIVER), linux-kernel@vger.kernel.org (open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)), linux-doc@vger.kernel.org (open list:DOCUMENTATION), linux-pm@vger.kernel.org (open list:AMD PSTATE DRIVER), Perry Yuan , Bagas Sanjaya Subject: [PATCH v10 01/13] Documentation: x86: Add AMD Hardware Feedback Interface documentation Date: Thu, 15 May 2025 16:19:38 -0500 Message-ID: <20250515211950.3102922-2-superm1@kernel.org> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20250515211950.3102922-1-superm1@kernel.org> References: <20250515211950.3102922-1-superm1@kernel.org> Precedence: bulk X-Mailing-List: linux-pm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 From: Perry Yuan Introduce a new documentation file, `amd_hfi.rst`, which delves into the implementation details of the AMD Hardware Feedback Interface and its associated driver, `amd_hfi`. This documentation describes how the driver provides hint to the OS scheduling which depends on the capability of core performance and efficiency ranking data. This documentation describes * The design of the driver * How the driver provides hints to the OS scheduling * How the driver interfaces with the kernel for efficiency ranking data. Reviewed-by: Bagas Sanjaya Signed-off-by: Perry Yuan Reviewed-by: Mario Limonciello Signed-off-by: Mario Limonciello --- Documentation/arch/x86/amd-hfi.rst | 133 +++++++++++++++++++++++++++++ Documentation/arch/x86/index.rst | 1 + 2 files changed, 134 insertions(+) create mode 100644 Documentation/arch/x86/amd-hfi.rst diff --git a/Documentation/arch/x86/amd-hfi.rst b/Documentation/arch/x86/amd-hfi.rst new file mode 100644 index 0000000000000..8c1799acb6fe6 --- /dev/null +++ b/Documentation/arch/x86/amd-hfi.rst @@ -0,0 +1,133 @@ +.. SPDX-License-Identifier: GPL-2.0 + +====================================================================== +Hardware Feedback Interface For Hetero Core Scheduling On AMD Platform +====================================================================== + +:Copyright: 2025 Advanced Micro Devices, Inc. All Rights Reserved. + +:Author: Perry Yuan +:Author: Mario Limonciello + +Overview +-------- + +AMD Heterogeneous Core implementations are comprised of more than one +architectural class and CPUs are comprised of cores of various efficiency and +power capabilities: performance-oriented *classic cores* and power-efficient +*dense cores*. As such, power management strategies must be designed to +accommodate the complexities introduced by incorporating different core types. +Heterogeneous systems can also extend to more than two architectural classes +as well. The purpose of the scheduling feedback mechanism is to provide +information to the operating system scheduler in real time such that the +scheduler can direct threads to the optimal core. + +The goal of AMD's heterogeneous architecture is to attain power benefit by +sending background thread to the dense cores while sending high priority +threads to the classic cores. From a performance perspective, sending +background threads to dense cores can free up power headroom and allow the +classic cores to optimally service demanding threads. Furthermore, the area +optimized nature of the dense cores allows for an increasing number of +physical cores. This improved core density will have positive multithreaded +performance impact. + +AMD Heterogeneous Core Driver +----------------------------- + +The ``amd_hfi`` driver delivers the operating system a performance and energy +efficiency capability data for each CPU in the system. The scheduler can use +the ranking data from the HFI driver to make task placement decisions. + +Thread Classification and Ranking Table Interaction +---------------------------------------------------- + +The thread classification is used to select into a ranking table that +describes an efficiency and performance ranking for each classification. + +Threads are classified during runtime into enumerated classes. The classes +represent thread performance/power characteristics that may benefit from +special scheduling behaviors. The below table depicts an example of thread +classification and a preference where a given thread should be scheduled +based on its thread class. The real time thread classification is consumed +by the operating system and is used to inform the scheduler of where the +thread should be placed. + +Thread Classification Example Table +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ++----------+----------------+-------------------------------+---------------------+---------+ +| class ID | Classification | Preferred scheduling behavior | Preemption priority | Counter | ++----------+----------------+-------------------------------+---------------------+---------+ +| 0 | Default | Performant | Highest | | ++----------+----------------+-------------------------------+---------------------+---------+ +| 1 | Non-scalable | Efficient | Lowest | PMCx1A1 | ++----------+----------------+-------------------------------+---------------------+---------+ +| 2 | I/O bound | Efficient | Lowest | PMCx044 | ++----------+----------------+-------------------------------+---------------------+---------+ + +Thread classification is performed by the hardware each time that the thread is switched out. +Threads that don't meet any hardware specified criteria will be classified as "default". + +AMD Hardware Feedback Interface +-------------------------------- + +The Hardware Feedback Interface provides to the operating system information +about the performance and energy efficiency of each CPU in the system. Each +capability is given as a unit-less quantity in the range [0-255]. A higher +performance value indicates higher performance capability, and a higher +efficiency value indicates more efficiency. Energy efficiency and performance +are reported in separate capabilities in the shared memory based ranking table. + +These capabilities may change at runtime as a result of changes in the +operating conditions of the system or the action of external factors. +Power Management FW is responsible for detecting events that would require +a reordering of the performance and efficiency ranking. Table updates would +happen relatively infrequently and occur on the time scale of seconds or more. + +The following events trigger a table update: + * Thermal Stress Events + * Silent Compute + * Extreme Low Battery Scenarios + +The kernel or a userspace policy daemon can use these capabilities to modify +task placement decisions. For instance, if either the performance or energy +capabilities of a given logical processor becomes zero, it is an indication +that the hardware recommends to the operating system to not schedule any tasks +on that processor for performance or energy efficiency reasons, respectively. + +Implementation details for Linux +-------------------------------- + +The implementation of threads scheduling consists of the following steps: + +1. A thread is spawned and scheduled to the ideal core using the default + heterogeneous scheduling policy. +2. The processor profiles thread execution and assigns an enumerated + classification ID. + This classification is communicated to the OS via logical processor + scope MSR. +3. During the thread context switch out the operating system consumes the + workload(WL) classification which resides in a logical processor scope MSR. +4. The OS triggers the hardware to clear its history by writing to an MSR, + after consuming the WL classification and before switching in the new thread. +5. If due to the classification, ranking table, and processor availability, + the thread is not on its ideal processor, the OS will then consider + scheduling the thread on its ideal processor (if available). + +Ranking Table +------------- +The ranking table is a shared memory region that is used to communicate the +performance and energy efficiency capabilities of each CPU in the system. + +The ranking table design includes rankings for each APIC ID in the system and +rankings both for performance and efficiency for each workload classification. + +.. kernel-doc:: drivers/platform/x86/amd/hfi/hfi.c + :doc: amd_shmem_info + +Ranking Table update +--------------------------- +The power management firmware issues an platform interrupt after updating the +ranking table and is ready for the operating system to consume it. CPUs receive +such interrupt and read new ranking table from shared memory which PCCT table +has provided, then ``amd_hfi`` driver parse the new table to provide new +consume data for scheduling decisions. diff --git a/Documentation/arch/x86/index.rst b/Documentation/arch/x86/index.rst index 58a006525ae81..cd9143d623872 100644 --- a/Documentation/arch/x86/index.rst +++ b/Documentation/arch/x86/index.rst @@ -28,6 +28,7 @@ x86-specific Documentation amd-debugging amd-memory-encryption amd_hsmp + amd-hfi tdx pti mds