docs: move x86 documentation into Documentation/arch/

Move the x86 documentation under Documentation/arch/ as a way of cleaning
up the top-level directory and making the structure of our docs more
closely match the structure of the source directories it describes.

All in-kernel references to the old paths have been updated.

Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: linux-arch@vger.kernel.org
Cc: x86@kernel.org
Cc: Borislav Petkov <bp@alien8.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/lkml/20230315211523.108836-1-corbet@lwn.net/
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

1 files changed, 0 insertions, 72 deletions

diff --git a/Documentation/x86/intel-hfi.rst b/Documentation/x86/intel-hfi.rst
deleted file mode 100644
index 49dea58ea4fb..000000000000
--- a/Documentation/x86/intel-hfi.rst
+++ /dev/null
@@ -1,72 +0,0 @@
-.. SPDX-License-Identifier: GPL-2.0
-
-============================================================
-Hardware-Feedback Interface for scheduling on Intel Hardware
-============================================================
-
-Overview
---------
-
-Intel has described the Hardware Feedback Interface (HFI) in the Intel 64 and
-IA-32 Architectures Software Developer's Manual (Intel SDM) Volume 3 Section
-14.6 [1]_.
-
-The HFI gives the operating system a performance and energy efficiency
-capability data for each CPU in the system. Linux can use the information from
-the HFI to influence task placement decisions.
-
-The 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]. Higher values
-indicate higher capability. Energy efficiency and performance are reported in
-separate capabilities. Even though on some systems these two metrics may be
-related, they are specified as independent capabilities in the Intel SDM.
-
-These capabilities may change at runtime as a result of changes in the
-operating conditions of the system or the action of external factors. The rate
-at which these capabilities are updated is specific to each processor model. On
-some models, capabilities are set at boot time and never change. On others,
-capabilities may change every tens of milliseconds. For instance, a remote
-mechanism may be used to lower Thermal Design Power. Such change can be
-reflected in the HFI. Likewise, if the system needs to be throttled due to
-excessive heat, the HFI may reflect reduced performance on specific CPUs.
-
-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 infrastructure to handle thermal event interrupts has two parts. In the
-Local Vector Table of a CPU's local APIC, there exists a register for the
-Thermal Monitor Register. This register controls how interrupts are delivered
-to a CPU when the thermal monitor generates and interrupt. Further details
-can be found in the Intel SDM Vol. 3 Section 10.5 [1]_.
-
-The thermal monitor may generate interrupts per CPU or per package. The HFI
-generates package-level interrupts. This monitor is configured and initialized
-via a set of machine-specific registers. Specifically, the HFI interrupt and
-status are controlled via designated bits in the IA32_PACKAGE_THERM_INTERRUPT
-and IA32_PACKAGE_THERM_STATUS registers, respectively. There exists one HFI
-table per package. Further details can be found in the Intel SDM Vol. 3
-Section 14.9 [1]_.
-
-The hardware issues an HFI interrupt after updating the HFI table and is ready
-for the operating system to consume it. CPUs receive such interrupt via the
-thermal entry in the Local APIC's Local Vector Table.
-
-When servicing such interrupt, the HFI driver parses the updated table and
-relays the update to userspace using the thermal notification framework. Given
-that there may be many HFI updates every second, the updates relayed to
-userspace are throttled at a rate of CONFIG_HZ jiffies.
-
-References
-----------
-
-.. [1] https://www.intel.com/sdm