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Tony Luck c2427e70c1 x86/resctrl: Implement new mba_MBps throttling heuristic
The mba_MBps feedback loop increases throttling when a group is using
more bandwidth than the target set by the user in the schemata file, and
decreases throttling when below target.

To avoid possibly stepping throttling up and down on every poll a flag
"delta_comp" is set whenever throttling is changed to indicate that the
actual change in bandwidth should be recorded on the next poll in
"delta_bw". Throttling is only reduced if the current bandwidth plus
delta_bw is below the user target.

This algorithm works well if the workload has steady bandwidth needs.
But it can go badly wrong if the workload moves to a different phase
just as the throttling level changed. E.g. if the workload becomes
essentially idle right as throttling level is increased, the value
calculated for delta_bw will be more or less the old bandwidth level.
If the workload then resumes, Linux may never reduce throttling because
current bandwidth plus delta_bw is above the target set by the user.

Implement a simpler heuristic by assuming that in the worst case the
currently measured bandwidth is being controlled by the current level of
throttling. Compute how much it may increase if throttling is relaxed to
the next higher level. If that is still below the user target, then it
is ok to reduce the amount of throttling.

Fixes: ba0f26d852 ("x86/intel_rdt/mba_sc: Prepare for feedback loop")
Reported-by: Xiaochen Shen <xiaochen.shen@intel.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Tested-by: Xiaochen Shen <xiaochen.shen@intel.com>
Link: https://lore.kernel.org/r/20240122180807.70518-1-tony.luck@intel.com
2024-01-24 11:32:01 +01:00
arch x86/resctrl: Implement new mba_MBps throttling heuristic 2024-01-24 11:32:01 +01:00
block for-6.8/block-2024-01-18 2024-01-18 18:22:40 -08:00
certs This update includes the following changes: 2023-11-02 16:15:30 -10:00
crypto crypto: scomp - fix req->dst buffer overflow 2023-12-29 11:25:56 +08:00
Documentation Updates for time and clocksources: 2024-01-21 11:14:40 -08:00
drivers Updates for time and clocksources: 2024-01-21 11:14:40 -08:00
fs More bcachefs updates for 6.7-rc1 2024-01-21 14:01:12 -08:00
include header cleanup fixup for 6.8-rc1 2024-01-21 10:21:43 -08:00
init Driver core changes for 6.8-rc1 2024-01-18 09:48:40 -08:00
io_uring for-6.8/io_uring-2024-01-18 2024-01-18 18:17:57 -08:00
ipc shm: Slim down dependencies 2023-12-20 19:26:31 -05:00
kernel Updates for time and clocksources: 2024-01-21 11:14:40 -08:00
lib RISC-V Patches for the 6.8 Merge Window, Part 4 2024-01-20 11:06:04 -08:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
mm vfs-6.8.netfs 2024-01-19 09:10:23 -08:00
net Assorted CephFS fixes and cleanups with nothing standing out. 2024-01-19 09:58:55 -08:00
rust Rust changes for v6.8 2024-01-11 13:05:41 -08:00
samples RISC-V Patches for the 6.8 Merge Window, Part 4 2024-01-20 11:06:04 -08:00
scripts Coccinelle change for v6.8 2024-01-20 14:20:34 -08:00
security + Features 2024-01-19 10:53:55 -08:00
sound sound fixes for 6.8-rc1 2024-01-19 12:30:29 -08:00
tools RISC-V Patches for the 6.8 Merge Window, Part 4 2024-01-20 11:06:04 -08:00
usr Kbuild updates for v6.8 2024-01-18 17:57:07 -08:00
virt Generic: 2024-01-17 13:03:37 -08:00
.clang-format clang-format: Update with v6.7-rc4's for_each macro list 2023-12-08 23:54:38 +01:00
.cocciconfig
.editorconfig Add .editorconfig file for basic formatting 2023-12-28 16:22:47 +09:00
.get_maintainer.ignore get_maintainer: add Alan to .get_maintainer.ignore 2022-08-20 15:17:44 -07:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore Add .editorconfig file for basic formatting 2023-12-28 16:22:47 +09:00
.mailmap Char/Misc and other Driver changes for 6.8-rc1 2024-01-17 16:47:17 -08:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS Including fixes from bpf and netfilter. 2024-01-18 17:33:50 -08:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS Various smb client fixes, including multichannel and for SMB3.1.1 POSIX extensions 2024-01-20 16:48:07 -08:00
Makefile Linux 6.8-rc1 2024-01-21 14:11:32 -08:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.