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Davidlohr Bueso 15df03c879 sysvipc: make get_maxid O(1) again
For a custom microbenchmark on a 3.30GHz Xeon SandyBridge, which calls
IPC_STAT over and over, it was calculated that, on avg the cost of
ipc_get_maxid() for increasing amounts of keys was:

 10 keys: ~900 cycles
 100 keys: ~15000 cycles
 1000 keys: ~150000 cycles
 10000 keys: ~2100000 cycles

This is unsurprising as maxid is currently O(n).

By having the max_id available in O(1) we save all those cycles for each
semctl(_STAT) command, the idr_find can be expensive -- which some real
(customer) workloads actually poll on.

Note that this used to be the case, until commit 7ca7e564e0 ("ipc:
store ipcs into IDRs").  The cost is the extra idr_find when doing
RMIDs, but we simply go backwards, and should not take too many
iterations to find the new value.

[akpm@linux-foundation.org: coding-style fixes]
Link: http://lkml.kernel.org/r/20170831172049.14576-5-dave@stgolabs.net
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-11-17 16:10:04 -08:00
arch pid: remove pidhash 2017-11-17 16:10:04 -08:00
block block/blk-mq.c: use kmalloc_array_node() 2017-11-15 18:21:02 -08:00
certs License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
crypto kmemcheck: stop using GFP_NOTRACK and SLAB_NOTRACK 2017-11-15 18:21:04 -08:00
Documentation kcov: update documentation 2017-11-17 16:10:04 -08:00
drivers drivers/watchdog: make use of devm_register_reboot_notifier() 2017-11-17 16:10:04 -08:00
firmware License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
fs pid: replace pid bitmap implementation with IDR API 2017-11-17 16:10:03 -08:00
include sysvipc: make get_maxid O(1) again 2017-11-17 16:10:04 -08:00
init initramfs: use time64_t timestamps 2017-11-17 16:10:04 -08:00
ipc sysvipc: make get_maxid O(1) again 2017-11-17 16:10:04 -08:00
kernel kernel/reboot.c: add devm_register_reboot_notifier() 2017-11-17 16:10:04 -08:00
lib Makefile: support flag -fsanitizer-coverage=trace-cmp 2017-11-17 16:10:04 -08:00
mm mm, compaction: remove unneeded pageblock_skip_persistent() checks 2017-11-17 16:10:00 -08:00
net Merge branch 'akpm' (patches from Andrew) 2017-11-15 19:42:40 -08:00
samples media updates for v4.15-rc1 2017-11-15 20:30:12 -08:00
scripts Makefile: support flag -fsanitizer-coverage=trace-cmp 2017-11-17 16:10:04 -08:00
security Modules updates for v4.15 2017-11-15 13:46:33 -08:00
sound sound updates for 4.15-rc1 2017-11-14 18:01:46 -08:00
tools tools/lib/traceevent/parse-filter.c: clean up clang build warning 2017-11-17 16:10:02 -08:00
usr initramfs: fix initramfs rebuilds w/ compression after disabling 2017-11-03 07:39:19 -07:00
virt First batch of KVM changes for 4.15 2017-11-16 13:00:24 -08:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Add hch to .get_maintainer.ignore 2015-08-21 14:30:10 -07:00
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore .gitignore: move *.dtb and *.dtb.S patterns to the top-level .gitignore 2017-11-08 11:20:24 -06:00
.mailmap Add Jason Gunthorpe as co-maintainer of the RDMA stack 2017-11-17 09:36:18 -08:00
COPYING
CREDITS MAINTAINERS: update TPM driver infrastructure changes 2017-11-09 17:58:40 -08:00
Kbuild License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
Kconfig License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
MAINTAINERS libnvdimm for 4.15 2017-11-17 09:51:57 -08:00
Makefile Makefile: support flag -fsanitizer-coverage=trace-cmp 2017-11-17 16:10:04 -08:00
README README: add a new README file, pointing to the Documentation/ 2016-10-24 08:12:35 -02:00

Linux kernel
============

This file was moved to Documentation/admin-guide/README.rst

Please notice that there are several guides for kernel developers and users.
These guides can be rendered in a number of formats, like HTML and PDF.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.

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.