core: implement a global thread pool

2019-02-18T02:58:24+00:00

This patch implements a thread pool that is wait-free for adding jobs to
the queue and uses a very small locked region to get jobs. This makes it
possible to decrease contention drastically. It's based on wfcqueue
structure provided by urcu library.

It automatically enables more threads when load demands it, and stops
them when not needed. There's a maximum number of threads that can be
used. This value can be configured.

Depending on the workload, the maximum number of threads plays an
important role. So it needs to be configured for optimal performance.
Currently the thread pool doesn't self adjust the maximum for the
workload, so this configuration needs to be changed manually.

For this reason, the global thread pool has been made optional, so that
volumes can still use the thread pool provided by io-threads.

To enable it for bricks, the following option needs to be set:

   config.global-threading = on

This option has no effect if bricks are already running. A restart is
required to activate it. It's recommended to also enable the following
option when running bricks with the global thread pool:

   performance.iot-pass-through = on

To enable it for a FUSE mount point, the option '--global-threading'
must be added to the mount command. To change it, an umount and remount
is needed. It's recommended to disable the following option when using
global threading on a mount point:

   performance.client-io-threads = off

To enable it for services managed by glusterd, glusterd needs to be
started with option '--global-threading'. In this case all daemons, like
self-heal, will be using the global thread pool.

Currently it can only be enabled for bricks, FUSE mounts and glusterd
services.

The maximum number of threads for clients and bricks can be configured
using the following options:

   config.client-threads
   config.brick-threads

These options can be applied online and its effect is immediate most of
the times. If one of them is set to 0, the maximum number of threads
will be calcutated as #cores * 2.

Some distributions use a very old userspace-rcu library (version 0.7)
for this reason, some header files from version 0.10 have been copied
into contrib/userspace-rcu and are used if the detected version is 0.7
or older.

An additional change has been made to io-threads to prevent that threads
are started when iot-pass-through is set.

Change-Id: I09d19e246b9e6d53c6247b29dfca6af6ee00a24b
updates: #532
Signed-off-by: Xavi Hernandez

build, glusterd: Add liburcu to build system

2015-02-23T12:35:37+00:00

This patch adds liburcu related checks to the build system and updates
the spec file to require 'userspace-rcu'.

liburcu >= 0.7 is required to build GlusterFS, but 0.8 and above is
preferred. For cases when liburcu 0.7.x is the available version, some
function definitions (currently just one) from liburcu-0.8.6 have been
made available in /contrib/userspace-rcu/.

This change was developed on the git branch at [1]. This commit is a
combination of the following commits on the development branch.
  a5cd6bd Add userspace-rcu checks to configure.ac
  fe5ced3 Add URCU libs to glusterd libtool flags
  1e43302 Add local definition of cds_list_add_tail_rcu for
          liburcu-0.7
  98da755 Move local definition of cds_list_add_tail_rcu into contrib
  8c44dfd Update spec file to include userspace-rcu0466e33 Rename
  rculist-additional.h to rculist-extra.h
  947c7b3 Add rculist-extra.h to dist
  19f32ad Address review comments 9605/1

[1]: https://github.com/kshlm/glusterfs/tree/urcu

Change-Id: Ifbb617d0dacce8fa01214f894badb9d8cdcaf56f
BUG: 1191030
Signed-off-by: Kaushal M 
Reviewed-on: http://review.gluster.org/9605
Tested-by: Gluster Build System 
Reviewed-by: Atin Mukherjee 
Reviewed-by: Niels de Vos 
Reviewed-by: Krishnan Parthasarathi 
Tested-by: Krishnan Parthasarathi

glusterfs.git/contrib/userspace-rcu, branch v9dev

core: implement a global thread pool

build, glusterd: Add liburcu to build system