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Filename Latest commit message Latest commit date
Rafael Aquini 29a132d793 ipc: replace costly bailout check in sysvipc_find_ipc() 
commit 20401d1058f3f841f35a594ac2fc1293710e55b9 upstream.

sysvipc_find_ipc() was left with a costly way to check if the offset
position fed to it is bigger than the total number of IPC IDs in use.  So
much so that the time it takes to iterate over /proc/sysvipc/* files grows
exponentially for a custom benchmark that creates "N" SYSV shm segments
and then times the read of /proc/sysvipc/shm (milliseconds):

    12 msecs to read   1024 segs from /proc/sysvipc/shm
    18 msecs to read   2048 segs from /proc/sysvipc/shm
    65 msecs to read   4096 segs from /proc/sysvipc/shm
   325 msecs to read   8192 segs from /proc/sysvipc/shm
  1303 msecs to read  16384 segs from /proc/sysvipc/shm
  5182 msecs to read  32768 segs from /proc/sysvipc/shm

The root problem lies with the loop that computes the total amount of ids
in use to check if the "pos" feeded to sysvipc_find_ipc() grew bigger than
"ids->in_use".  That is a quite inneficient way to get to the maximum
index in the id lookup table, specially when that value is already
provided by struct ipc_ids.max_idx.

This patch follows up on the optimization introduced via commit
15df03c879 ("sysvipc: make get_maxid O(1) again") and gets rid of the
aforementioned costly loop replacing it by a simpler checkpoint based on
ipc_get_maxidx() returned value, which allows for a smooth linear increase
in time complexity for the same custom benchmark:

     2 msecs to read   1024 segs from /proc/sysvipc/shm
     2 msecs to read   2048 segs from /proc/sysvipc/shm
     4 msecs to read   4096 segs from /proc/sysvipc/shm
     9 msecs to read   8192 segs from /proc/sysvipc/shm
    19 msecs to read  16384 segs from /proc/sysvipc/shm
    39 msecs to read  32768 segs from /proc/sysvipc/shm

Link: https://lkml.kernel.org/r/20210809203554.1562989-1-aquini@redhat.com
Signed-off-by: Rafael Aquini <aquini@redhat.com>
Acked-by: Davidlohr Bueso <dbueso@suse.de>
Acked-by: Manfred Spraul <manfred@colorfullife.com>
Cc: Waiman Long <llong@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2024-09-04 13:15:02 +02:00
arch openrisc: Call setup_memory() earlier in the init sequence 2024-09-04 13:14:57 +02:00
block block: prevent division by zero in blk_rq_stat_sum() 2024-04-13 12:51:38 +02:00
certs
crypto crypto: ecrdsa - Fix module auto-load on add_key 2024-06-16 13:28:51 +02:00
Documentation overflow: Implement size_t saturating arithmetic helpers 2024-09-04 13:14:51 +02:00
drivers wifi: mwifiex: duplicate static structs used in driver instances 2024-09-04 13:15:02 +02:00
fs ext4: set the type of max_zeroout to unsigned int to avoid overflow 2024-09-04 13:14:57 +02:00
include kcm: Serialise kcm_sendmsg() for the same socket. 2024-09-04 13:14:59 +02:00
init init: open /initrd.image with O_LARGEFILE 2024-04-13 12:51:36 +02:00
ipc ipc: replace costly bailout check in sysvipc_find_ipc() 2024-09-04 13:15:02 +02:00
kernel hrtimer: Prevent queuing of hrtimer without a function callback 2024-09-04 13:14:58 +02:00
lib overflow: Implement size_t saturating arithmetic helpers 2024-09-04 13:14:51 +02:00
LICENSES
mm memcg_write_event_control(): fix a user-triggerable oops 2024-09-04 13:14:50 +02:00
net Bluetooth: MGMT: Add error handling to pair_device() 2024-09-04 13:15:01 +02:00
samples media: rename VFL_TYPE_GRABBER to _VIDEO 2024-03-26 18:22:22 -04:00
scripts kbuild: Fix '-S -c' in x86 stack protector scripts 2024-08-19 05:33:53 +02:00
security selinux: fix potential counting error in avc_add_xperms_decision() 2024-09-04 13:14:50 +02:00
sound ALSA: timer: Relax start tick time check for slave timer elements 2024-09-04 13:15:01 +02:00
tools tools: move alignment-related macros to new <linux/align.h> 2024-09-04 13:15:02 +02:00
usr
virt KVM: async_pf: Cleanup kvm_setup_async_pf() 2024-05-02 16:18:32 +02:00
.clang-format
.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore
.mailmap
COPYING
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Kbuild
Kconfig
MAINTAINERS
Makefile Linux 5.4.282 2024-08-19 05:33:54 +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.