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Nícolas F. R. A. Prado fb64fc9fac thermal: core: Don't update trip points inside the hysteresis range 
[ Upstream commit cf3986f8c0 ]

When searching for the trip points that need to be set, the nearest
higher trip point's temperature is used for the high trip, while the
nearest lower trip point's temperature minus the hysteresis is used for
the low trip. The issue with this logic is that when the current
temperature is inside a trip point's hysteresis range, both high and low
trips will come from the same trip point. As a consequence instability
can still occur like this:
* the temperature rises slightly and enters the hysteresis range of a
  trip point
* polling happens and updates the trip points to the hysteresis range
* the temperature falls slightly, exiting the hysteresis range, crossing
  the trip point and triggering an IRQ, the trip points are updated
* repeat

So even though the current hysteresis implementation prevents
instability from happening due to IRQs triggering on the same
temperature value, both ways, it doesn't prevent it from happening due
to an IRQ on one way and polling on the other.

To properly implement a hysteresis behavior, when inside the hysteresis
range, don't update the trip points. This way, the previously set trip
points will stay in effect, which will in a way remember the previous
state (if the temperature signal came from above or below the range) and
therefore have the right trip point already set.

The exception is if there was no previous trip point set, in which case
a previous state doesn't exist, and so it's sensible to allow the
hysteresis range as trip points.

The following logs show the current behavior when running on a real
machine:

[  202.524658] thermal thermal_zone0: new temperature boundaries: -2147483647 < x < 40000
   203.562817: thermal_temperature: thermal_zone=vpu0-thermal id=0 temp_prev=36986 temp=37979
[  203.562845] thermal thermal_zone0: new temperature boundaries: 37000 < x < 40000
   204.176059: thermal_temperature: thermal_zone=vpu0-thermal id=0 temp_prev=37979 temp=40028
[  204.176089] thermal thermal_zone0: new temperature boundaries: 37000 < x < 100000
   205.226813: thermal_temperature: thermal_zone=vpu0-thermal id=0 temp_prev=40028 temp=38652
[  205.226842] thermal thermal_zone0: new temperature boundaries: 37000 < x < 40000

And with this patch applied:

[  184.933415] thermal thermal_zone0: new temperature boundaries: -2147483647 < x < 40000
   185.981182: thermal_temperature: thermal_zone=vpu0-thermal id=0 temp_prev=36986 temp=37872
   186.744685: thermal_temperature: thermal_zone=vpu0-thermal id=0 temp_prev=37872 temp=40058
[  186.744716] thermal thermal_zone0: new temperature boundaries: 37000 < x < 100000
   187.773284: thermal_temperature: thermal_zone=vpu0-thermal id=0 temp_prev=40058 temp=38698

Fixes: 060c034a97 ("thermal: Add support for hardware-tracked trip points")
Signed-off-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Co-developed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2023-11-20 11:59:01 +01:00
arch bpf, x64: Fix tailcall infinite loop 2023-11-20 11:58:55 +01:00
block blk-throttle: check for overflow in calculate_bytes_allowed 2023-10-20 18:38:17 -06:00
certs certs: Reference revocation list for all keyrings 2023-08-17 20:12:41 +00:00
crypto KEYS: asymmetric: Fix sign/verify on pkcs1pad without a hash 2023-10-18 12:27:10 +08:00
Documentation x86/srso: Fix vulnerability reporting for missing microcode 2023-11-20 11:58:52 +01:00
drivers thermal: core: Don't update trip points inside the hysteresis range 2023-11-20 11:59:01 +01:00
fs pstore/platform: Add check for kstrdup 2023-11-20 11:58:53 +01:00
include PM: sleep: Fix symbol export for _SIMPLE_ variants of _PM_OPS() 2023-11-20 11:58:57 +01:00
init workqueue: Changes for v6.6 2023-09-01 16:06:32 -07:00
io_uring assorted fixes all over the place 2023-10-27 16:44:58 -10:00
ipc Add x86 shadow stack support 2023-08-31 12:20:12 -07:00
kernel bpf: Fix missed rcu read lock in bpf_task_under_cgroup() 2023-11-20 11:59:01 +01:00
lib maple_tree: add GFP_KERNEL to allocations in mas_expected_entries() 2023-10-18 12:12:41 -07:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
mm vfs: fix readahead(2) on block devices 2023-11-20 11:58:52 +01:00
net net: skb_find_text: Ignore patterns extending past 'to' 2023-11-20 11:59:01 +01:00
rust rust: docs: fix logo replacement 2023-10-19 16:40:00 +02:00
samples VFIO updates for v6.6-rc1 2023-08-30 20:36:01 -07:00
scripts x86/srso: Fix unret validation dependencies 2023-11-20 11:58:52 +01:00
security KEYS: trusted: Remove redundant static calls usage 2023-10-10 11:19:43 -07:00
sound ASoC: SOF: sof-pci-dev: Fix community key quirk detection 2023-11-08 11:56:24 +01:00
tools selftests/bpf: Make linked_list failure test more robust 2023-11-20 11:59:01 +01:00
usr initramfs: Encode dependency on KBUILD_BUILD_TIMESTAMP 2023-06-06 17:54:49 +09:00
virt ARM: 2023-09-07 13:52:20 -07:00
.clang-format iommu: Add for_each_group_device() 2023-05-23 08:15:51 +02:00
.cocciconfig
.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 kbuild: rpm-pkg: rename binkernel.spec to kernel.spec 2023-07-25 00:59:33 +09:00
.mailmap 20 hotfixes. 12 are cc:stable and the remainder address post-6.5 issues 2023-10-24 09:52:16 -10:00
.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 USB: Remove Wireless USB and UWB documentation 2023-08-09 14:17:32 +02:00
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 Char/Misc driver fixes for 6.6-final 2023-10-28 07:51:27 -10:00
Makefile Linux 6.6.1 2023-11-08 11:56:25 +01:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

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.