github-mirror/linux
1
0
Fork 0
mirror of https://github.com/torvalds/linux.git synced 2026-06-08 22:52:35 +02:00
Code Issues Actions Packages Projects Releases Wiki Activity Graph
Linux kernel source tree
800,937 Commits 1 Branch 934 Tags 20 GiB
C 97%
Assembly 1%
Shell 0.6%
Rust 0.5%
Python 0.4%
Other 0.3%
420646bfc8
Go to file
Fenghua Yu 420646bfc8 x86/resctrl: Use an IPI instead of task_work_add() to update PQR_ASSOC MSR 
commit ae28d1aae4 upstream

Currently, when moving a task to a resource group the PQR_ASSOC MSR is
updated with the new closid and rmid in an added task callback. If the
task is running, the work is run as soon as possible. If the task is not
running, the work is executed later in the kernel exit path when the
kernel returns to the task again.

Updating the PQR_ASSOC MSR as soon as possible on the CPU a moved task
is running is the right thing to do. Queueing work for a task that is
not running is unnecessary (the PQR_ASSOC MSR is already updated when
the task is scheduled in) and causing system resource waste with the way
in which it is implemented: Work to update the PQR_ASSOC register is
queued every time the user writes a task id to the "tasks" file, even if
the task already belongs to the resource group.

This could result in multiple pending work items associated with a
single task even if they are all identical and even though only a single
update with most recent values is needed. Specifically, even if a task
is moved between different resource groups while it is sleeping then it
is only the last move that is relevant but yet a work item is queued
during each move.

This unnecessary queueing of work items could result in significant
system resource waste, especially on tasks sleeping for a long time.
For example, as demonstrated by Shakeel Butt in [1] writing the same
task id to the "tasks" file can quickly consume significant memory. The
same problem (wasted system resources) occurs when moving a task between
different resource groups.

As pointed out by Valentin Schneider in [2] there is an additional issue
with the way in which the queueing of work is done in that the task_struct
update is currently done after the work is queued, resulting in a race with
the register update possibly done before the data needed by the update is
available.

To solve these issues, update the PQR_ASSOC MSR in a synchronous way
right after the new closid and rmid are ready during the task movement,
only if the task is running. If a moved task is not running nothing
is done since the PQR_ASSOC MSR will be updated next time the task is
scheduled. This is the same way used to update the register when tasks
are moved as part of resource group removal.

[1] https://lore.kernel.org/lkml/CALvZod7E9zzHwenzf7objzGKsdBmVwTgEJ0nPgs0LUFU3SN5Pw@mail.gmail.com/
[2] https://lore.kernel.org/lkml/20201123022433.17905-1-valentin.schneider@arm.com

 [ bp: Massage commit message and drop the two update_task_closid_rmid()
   variants. ]

Backporting notes:

Since upstream commit fa7d949337 ("x86/resctrl: Rename and move rdt
files to a separate directory"), the file
arch/x86/kernel/cpu/intel_rdt_rdtgroup.c has been renamed and moved to
arch/x86/kernel/cpu/resctrl/rdtgroup.c.
Apply the change against file arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
for older stable trees.

Since upstream commit 352940ecec ("x86/resctrl: Rename the RDT
functions and definitions"), resctrl functions received more generic
names. Specifically related to this backport, intel_rdt_sched_in()
was renamed to rescrl_sched_in().

Fixes: e02737d5b8 ("x86/intel_rdt: Add tasks files")
Reported-by: Shakeel Butt <shakeelb@google.com>
Reported-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Reviewed-by: James Morse <james.morse@arm.com>
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/17aa2fb38fc12ce7bb710106b3e7c7b45acb9e94.1608243147.git.reinette.chatre@intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2021-01-17 14:04:20 +01:00
arch x86/resctrl: Use an IPI instead of task_work_add() to update PQR_ASSOC MSR 2021-01-17 14:04:20 +01:00
block block: factor out requeue handling from dispatch code 2020-12-30 11:25:45 +01:00
certs export.h: remove VMLINUX_SYMBOL() and VMLINUX_SYMBOL_STR() 2018-08-22 23:21:44 +09:00
crypto crypto: ecdh - avoid buffer overflow in ecdh_set_secret() 2021-01-12 20:10:20 +01:00
Documentation USB: UAS: introduce a quirk to set no_write_same 2020-12-30 11:25:42 +01:00
drivers chtls: Fix chtls resources release sequence 2021-01-17 14:04:20 +01:00
firmware Fix built-in early-load Intel microcode alignment 2020-01-23 08:21:29 +01:00
fs btrfs: send: fix wrong file path when there is an inode with a pending rmdir 2021-01-12 20:10:24 +01:00
include net: sched: prevent invalid Scell_log shift count 2021-01-12 20:10:20 +01:00
init printk: reduce LOG_BUF_SHIFT range for H8300 2020-11-05 11:08:41 +01:00
ipc ipc/util.c: sysvipc_find_ipc() incorrectly updates position index 2020-05-20 08:18:40 +02:00
kernel workqueue: Kick a worker based on the actual activation of delayed works 2021-01-12 20:10:16 +01:00
lib lib/genalloc: fix the overflow when size is too big 2021-01-12 20:10:16 +01:00
LICENSES LICENSES: Remove CC-BY-SA-4.0 license text 2018-10-18 11:28:50 +02:00
mm mm/swapfile: do not sleep with a spin lock held 2020-12-11 13:25:02 +01:00
net net: ipv6: fib: flush exceptions when purging route 2021-01-17 14:04:19 +01:00
samples samples: bpf: Fix lwt_len_hist reusing previous BPF map 2020-12-30 11:25:57 +01:00
scripts depmod: handle the case of /sbin/depmod without /sbin in PATH 2021-01-12 20:10:16 +01:00
security ima: Don't modify file descriptor mode on the fly 2020-12-30 11:26:12 +01:00
sound ALSA: hda/realtek - Fix speaker volume control on Lenovo C940 2021-01-12 20:10:24 +01:00
tools perf record: Fix memory leak when using '--user-regs=?' to list registers 2020-12-30 11:26:05 +01:00
usr initramfs: restore default compression behavior 2020-04-13 10:44:59 +02:00
virt KVM: arm64: vgic-v3: Drop the reporting of GICR_TYPER.Last for userspace 2020-12-02 08:48:07 +01:00
.clang-format clang-format: Set IndentWrappedFunctionNames false 2018-08-01 18:38:51 +02:00
.cocciconfig
.get_maintainer.ignore
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Kbuild updates for v4.17 (2nd) 2018-04-15 17:21:30 -07:00
.mailmap libnvdimm-for-4.19_misc 2018-08-25 18:13:10 -07:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS 9p: remove Ron Minnich from MAINTAINERS 2018-08-17 16:20:26 -07:00
Kbuild Kbuild updates for v4.15 2017-11-17 17:45:29 -08:00
Kconfig kconfig: move the "Executable file formats" menu to fs/Kconfig.binfmt 2018-08-02 08:06:55 +09:00
MAINTAINERS Documentation/llvm: add documentation on building w/ Clang/LLVM 2020-09-26 18:01:31 +02:00
Makefile Linux 4.19.167 2021-01-12 20:10:25 +01:00
README Docs: Added a pointer to the formatted docs to README 2018-03-21 09:02:53 -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.
See Documentation/00-INDEX for a list of what is contained in each file.

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.