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Filename Latest commit message Latest commit date
Michal Koutný 059516952c cgroup: Optimize single thread migration 
[ Upstream commit 9a3284fad42f66bb43629c6716709ff791aaa457 ]

There are reports of users who use thread migrations between cgroups and
they report performance drop after d59cfc09c3 ("sched, cgroup: replace
signal_struct->group_rwsem with a global percpu_rwsem"). The effect is
pronounced on machines with more CPUs.

The migration is affected by forking noise happening in the background,
after the mentioned commit a migrating thread must wait for all
(forking) processes on the system, not only of its threadgroup.

There are several places that need to synchronize with migration:
	a) do_exit,
	b) de_thread,
	c) copy_process,
	d) cgroup_update_dfl_csses,
	e) parallel migration (cgroup_{proc,thread}s_write).

In the case of self-migrating thread, we relax the synchronization on
cgroup_threadgroup_rwsem to avoid the cost of waiting. d) and e) are
excluded with cgroup_mutex, c) does not matter in case of single thread
migration and the executing thread cannot exec(2) or exit(2) while it is
writing into cgroup.threads. In case of do_exit because of signal
delivery, we either exit before the migration or finish the migration
(of not yet PF_EXITING thread) and die afterwards.

This patch handles only the case of self-migration by writing "0" into
cgroup.threads. For simplicity, we always take cgroup_threadgroup_rwsem
with numeric PIDs.

This change improves migration dependent workload performance similar
to per-signal_struct state.

Signed-off-by: Michal Koutný <mkoutny@suse.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2022-09-15 12:04:54 +02:00
arch arm64: cacheinfo: Fix incorrect assignment of signed error value to unsigned fw_level 2022-09-15 12:04:54 +02:00
block blk-mq: don't create hctx debugfs dir until q->debugfs_dir is created 2022-08-25 11:17:36 +02:00
certs certs/blacklist_hashes.c: fix const confusion in certs blacklist 2022-06-22 14:11:22 +02:00
crypto crypto: drbg - make reseeding from get_random_bytes() synchronous 2022-06-22 14:11:18 +02:00
Documentation x86/bugs: Add "unknown" reporting for MMIO Stale Data 2022-09-05 10:27:45 +02:00
drivers scsi: lpfc: Add missing destroy_workqueue() in error path 2022-09-15 12:04:54 +02:00
fs debugfs: add debugfs_lookup_and_remove() 2022-09-15 12:04:54 +02:00
include debugfs: add debugfs_lookup_and_remove() 2022-09-15 12:04:54 +02:00
init random: handle latent entropy and command line from random_init() 2022-06-22 14:11:17 +02:00
ipc ipc/mqueue: use get_tree_nodev() in mqueue_get_tree() 2022-06-14 18:11:41 +02:00
kernel cgroup: Optimize single thread migration 2022-09-15 12:04:54 +02:00
lib lib/vdso: Mark do_hres() and do_coarse() as __always_inline 2022-09-05 10:27:47 +02:00
LICENSES
mm Revert "mm: kmemleak: take a full lowmem check in kmemleak_*_phys()" 2022-09-15 12:04:49 +02:00
net net: mac802154: Fix a condition in the receive path 2022-09-15 12:04:53 +02:00
samples samples/kretprobes: Fix return value if register_kretprobe() failed 2021-11-17 09:48:39 +01:00
scripts kbuild: Fix include path in scripts/Makefile.modpost 2022-09-05 10:27:45 +02:00
security apparmor: Fix memleak in aa_simple_write_to_buffer() 2022-08-25 11:18:21 +02:00
sound ALSA: usb-audio: Fix an out-of-bounds bug in __snd_usb_parse_audio_interface() 2022-09-15 12:04:54 +02:00
tools Revert "selftests/bpf: Fix test_align verifier log patterns" 2022-09-05 10:27:39 +02:00
usr
virt KVM: Add infrastructure and macro to mark VM as bugged 2022-08-25 11:18:16 +02:00
.clang-format
.cocciconfig
.get_maintainer.ignore
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COPYING
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Kbuild
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MAINTAINERS MAINTAINERS: co-maintain random.c 2022-06-22 14:11:05 +02:00
Makefile Linux 5.4.212 2022-09-05 10:27:48 +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.