linux

Go to file

Michael Wang dd39eadc71 sched: Avoid scale real weight down to zero [ Upstream commit `26cf52229e` ] During our testing, we found a case that shares no longer working correctly, the cgroup topology is like: /sys/fs/cgroup/cpu/A (shares=102400) /sys/fs/cgroup/cpu/A/B (shares=2) /sys/fs/cgroup/cpu/A/B/C (shares=1024) /sys/fs/cgroup/cpu/D (shares=1024) /sys/fs/cgroup/cpu/D/E (shares=1024) /sys/fs/cgroup/cpu/D/E/F (shares=1024) The same benchmark is running in group C & F, no other tasks are running, the benchmark is capable to consumed all the CPUs. We suppose the group C will win more CPU resources since it could enjoy all the shares of group A, but it's F who wins much more. The reason is because we have group B with shares as 2, since A->cfs_rq.load.weight == B->se.load.weight == B->shares/nr_cpus, so A->cfs_rq.load.weight become very small. And in calc_group_shares() we calculate shares as: load = max(scale_load_down(cfs_rq->load.weight), cfs_rq->avg.load_avg); shares = (tg_shares * load) / tg_weight; Since the 'cfs_rq->load.weight' is too small, the load become 0 after scale down, although 'tg_shares' is 102400, shares of the se which stand for group A on root cfs_rq become 2. While the se of D on root cfs_rq is far more bigger than 2, so it wins the battle. Thus when scale_load_down() scale real weight down to 0, it's no longer telling the real story, the caller will have the wrong information and the calculation will be buggy. This patch add check in scale_load_down(), so the real weight will be >= MIN_SHARES after scale, after applied the group C wins as expected. Suggested-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Michael Wang <yun.wang@linux.alibaba.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org> Link: https://lkml.kernel.org/r/38e8e212-59a1-64b2-b247-b6d0b52d8dc1@linux.alibaba.com Signed-off-by: Sasha Levin <sashal@kernel.org>		2020-04-17 10:50:02 +02:00
arch	x86: Don't let pgprot_modify() change the page encryption bit	2020-04-17 10:50:01 +02:00
block	block: keep bdi->io_pages in sync with max_sectors_kb for stacked devices	2020-04-17 10:50:01 +02:00
certs
crypto
Documentation	dt-bindings: net: FMan erratum A050385	2020-04-01 11:01:52 +02:00
drivers	media: allegro: fix type of gop_length in channel_create message	2020-04-17 10:50:02 +02:00
fs	debugfs: Check module state before warning in {full/open}_proxy_open()	2020-04-17 10:50:02 +02:00
include	media: rc: add keymap for Videostrong KII Pro	2020-04-17 10:49:59 +02:00
init
ipc
kernel	sched: Avoid scale real weight down to zero	2020-04-17 10:50:02 +02:00
lib	uapi: rename ext2_swab() to swab() and share globally in swab.h	2020-04-13 10:48:07 +02:00
LICENSES
mm	slub: improve bit diffusion for freelist ptr obfuscation	2020-04-13 10:48:07 +02:00
net	cfg80211: Do not warn on same channel at the end of CSA	2020-04-17 10:49:59 +02:00
samples
scripts	kconfig: introduce m32-flag and m64-flag	2020-04-08 09:08:37 +02:00
security
sound	ASoC: jz4740-i2s: Fix divider written at incorrect offset in register	2020-04-13 10:48:09 +02:00
tools	selftests/net: add definition for SOL_DCCP to fix compilation errors for old libc	2020-04-17 10:49:59 +02:00
usr	initramfs: restore default compression behavior	2020-04-08 09:08:38 +02:00
virt
.clang-format
.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore
.mailmap
COPYING
CREDITS
Kbuild
Kconfig
MAINTAINERS
Makefile	Linux 5.4.32	2020-04-13 10:48:18 +02:00
README

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.