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Tejun Heo 894d9cd524 iocost: don't let vrate run wild while there's no saturation signal 
[ Upstream commit 81ca627a93 ]

When the QoS targets are met and nothing is being throttled, there's
no way to tell how saturated the underlying device is - it could be
almost entirely idle, at the cusp of saturation or anywhere inbetween.
Given that there's no information, it's best to keep vrate as-is in
this state.  Before 7cd806a9a9 ("iocost: improve nr_lagging
handling"), this was the case - if the device isn't missing QoS
targets and nothing is being throttled, busy_level was reset to zero.

While fixing nr_lagging handling, 7cd806a9a9 ("iocost: improve
nr_lagging handling") broke this.  Now, while the device is hitting
QoS targets and nothing is being throttled, vrate keeps getting
adjusted according to the existing busy_level.

This led to vrate keeping climing till it hits max when there's an IO
issuer with limited request concurrency if the vrate started low.
vrate starts getting adjusted upwards until the issuer can issue IOs
w/o being throttled.  From then on, QoS targets keeps getting met and
nothing on the system needs throttling and vrate keeps getting
increased due to the existing busy_level.

This patch makes the following changes to the busy_level logic.

* Reset busy_level if nr_shortages is zero to avoid the above
  scenario.

* Make non-zero nr_lagging block lowering nr_level but still clear
  positive busy_level if there's clear non-saturation signal - QoS
  targets are met and nr_shortages is non-zero.  nr_lagging's role is
  preventing adjusting vrate upwards while there are long-running
  commands and it shouldn't keep busy_level positive while there's
  clear non-saturation signal.

* Restructure code for clarity and add comments.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Andy Newell <newella@fb.com>
Fixes: 7cd806a9a9 ("iocost: improve nr_lagging handling")
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2020-06-22 09:31:06 +02:00
arch mips: cm: Fix an invalid error code of INTVN_*_ERR 2020-06-22 09:31:03 +02:00
block iocost: don't let vrate run wild while there's no saturation signal 2020-06-22 09:31:06 +02:00
certs PKCS#7: Refactor verify_pkcs7_signature() 2019-08-05 18:40:18 -04:00
crypto crypto: drbg - fix error return code in drbg_alloc_state() 2020-06-17 16:40:31 +02:00
Documentation dt-bindings: display: mediatek: control dpi pins mode to avoid leakage 2020-06-22 09:30:58 +02:00
drivers raid5: remove gfp flags from scribble_alloc() 2020-06-22 09:31:06 +02:00
fs xfs: fix duplicate verification from xfs_qm_dqflush() 2020-06-22 09:31:03 +02:00
include kgdb: Fix spurious true from in_dbg_master() 2020-06-22 09:31:03 +02:00
init x86: Fix early boot crash on gcc-10, third try 2020-05-20 08:20:34 +02:00
ipc ipc/util.c: sysvipc_find_ipc() incorrectly updates position index 2020-05-20 08:20:16 +02:00
kernel sched/core: Fix illegal RCU from offline CPUs 2020-06-22 09:31:01 +02:00
lib lib/mpi: Fix 64-bit MIPS build with Clang 2020-06-22 09:31:00 +02:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
mm mm/slub: fix a memory leak in sysfs_slab_add() 2020-06-17 16:40:36 +02:00
net netfilter: nft_nat: return EOPNOTSUPP if type or flags are not supported 2020-06-22 09:31:00 +02:00
samples samples: bpf: Fix build error 2020-06-03 08:21:15 +02:00
scripts bpf: Support llvm-objcopy for vmlinux BTF 2020-06-17 16:40:20 +02:00
security selinux: fix error return code in policydb_read() 2020-06-22 09:31:01 +02:00
sound ALSA: usb-audio: Add vendor, product and profile name for HP Thunderbolt Dock 2020-06-17 16:40:28 +02:00
tools iocost_monitor: drop string wrap around numbers when outputting json 2020-06-22 09:31:01 +02:00
usr initramfs: restore default compression behavior 2020-04-08 09:08:38 +02:00
virt KVM: arm64: Save the host's PtrAuth keys in non-preemptible context 2020-06-17 16:40:38 +02:00
.clang-format clang-format: Update with the latest for_each macro list 2019-08-31 10:00:51 +02:00
.cocciconfig
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Modules updates for v5.4 2019-09-22 10:34:46 -07:00
.mailmap ARM: SoC fixes 2019-11-10 13:41:59 -08:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS MAINTAINERS: Remove Simon as Renesas SoC Co-Maintainer 2019-10-10 08:12:51 -07:00
Kbuild kbuild: do not descend to ./Kbuild when cleaning 2019-08-21 21:03:58 +09:00
Kconfig docs: kbuild: convert docs to ReST and rename to *.rst 2019-06-14 14:21:21 -06:00
MAINTAINERS MAINTAINERS: Update drm/i915 bug filing URL 2020-02-28 17:22:19 +01:00
Makefile Linux 5.4.47 2020-06-17 16:40:38 +02:00
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.