16d4acbaca
The 'D' is now capital to clarify pronunciation. DBus service name is kept as '/Tuned' not to break backward compatibility. This will also need update of downstream tests which rely on the specific output strings containing the name. Signed-off-by: Jaroslav Škarvada <jskarvad@redhat.com>
112 lines
4.6 KiB
Groff
112 lines
4.6 KiB
Groff
.\"/*
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.\" * All rights reserved
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.\" * Copyright (C) 2015-2017 Red Hat, Inc.
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.\" * Authors: Jaroslav Škarvada, Luiz Capitulino
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.\" *
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.\" * This program is free software; you can redistribute it and/or
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.\" * modify it under the terms of the GNU General Public License
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.\" * as published by the Free Software Foundation; either version 2
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.\" * of the License, or (at your option) any later version.
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.\" *
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.\" * This program is distributed in the hope that it will be useful,
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.\" * but WITHOUT ANY WARRANTY; without even the implied warranty of
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.\" * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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.\" * GNU General Public License for more details.
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.\" *
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.\" * You should have received a copy of the GNU General Public License
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.\" * along with this program; if not, write to the Free Software
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.\" * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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.\" */
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.\"
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.TH TUNED_PROFILES_CPU_PARTITIONING "7" "22 Feb 2018" "TuneD"
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.SH NAME
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tuned\-profiles\-cpu\-partitioning - Partition CPUs into isolated and housekeeping.
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.SH DESCRIPTION
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The cpu\-partitioning profile partitions the system CPUs into isolated and
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housekeeping CPUs. This profile is intended to be used for latency\-sensitive
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workloads.
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An isolated CPU incurs reduced jitter and reduced interruptions by the
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kernel. This is achieved by clearing the CPU from user\-space processes, movable
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kernel threads, interruption handlers, kernel timers, etc. The only fixed
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source of interruptions is the 1Hz tick maintained by the kernel to keep
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CPU usage statistics. Otherwise, the incurred jitter and interruptions, if
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any, depend on the kernel services used by the thread running on the isolated
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CPU. Threads that run a busy loop without doing system calls, such as
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user\-space drivers that access the hardware directly, are only expected to
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be interrupted once a second by the 1Hz tick.
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A housekeeping CPU is the opposite of an isolated CPU. Housekeeping CPUs
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run all daemons, shell processes, kernel threads, interruption handlers
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and work that can be dispatched from isolated CPUs such as disk I/O,
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RCU work, timers, etc.
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.SH CONFIGURATION
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The cpu-partitioning profile is configured by editing the
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.I /etc/tuned/cpu-partitioning-variables.conf
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file. There are two configuration options:
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.TP
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.B isolated_cores=<CPU\-LIST>
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List of CPUs to isolate. This option is mandatory. Any CPUs not in this list
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is automatically considered a housekeeping CPU.
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.TP
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.B no_balance_cores=<CPU\-LIST>
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List of CPUs not be considered by the kernel when doing system wide
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process load\-balancing. Usually, this list should be the same as
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isolated_cores=. This option is optional.
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.SH IMPORTANT NOTES
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.IP * 2
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The system should be rebooted after applying the cpu\-partitioning profile
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for the first time or changing its configuration
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.IP *
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The cpu\-partitioning profile can be used in bare\-metal and virtual machines
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.IP *
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When using the cpu\-partitioning profile in bare\-metal, it is strongly
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recommended to "mask" the ksm and ksmtuned services in systemd (if they are
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installed). This can be done with the following command:
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# systemctl mask ksm ksmtuned
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.IP *
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The cpu\-partitioning profile does not use the kernel's isolcpus= feature
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.IP *
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On a NUMA system, it is recommended to have at least one housekeeping CPU
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per NUMA node
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.IP *
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The cpu\-partitioning profile does not support isolating the L3 cache. This
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means that a housekeeping CPU can still thrash cache entries pertaining to
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isolated CPUs. It is recommended to use cache isolation technologies to remedy
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this problem, such as Intel's Cache Allocation Technology
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.IP *
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Whether or not the kernel is going to be able to deactivate the tick on
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isolated CPUs depend on a few factors concerning the running thread behavior.
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Please, consult the nohz_full documentation in the kernel to learn more
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.IP *
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The Linux real\-time project has put together a document on the best
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practices for writing real\-time applications. Even though the
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cpu\-partitioning profile does not guarantee real\-time response time, much
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of the techniques for writing real\-time applications also apply for
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applications intended to run under the cpu\-partitioning profile. Please,
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refer to this document at
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.I https://rt.wiki.kernel.org
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.SH "FILES"
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.nf
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.I /etc/tuned/cpu\-partitioning\-variables.conf
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.I /etc/tuned/tuned\-main.conf
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.SH "SEE ALSO"
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.BR tuned (8)
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.BR tuned\-adm (8)
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.BR tuned\-profiles (7)
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.BR tuned\-profiles\-realtime (7)
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.BR tuned\-profiles\-nfv\-host (7)
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.BR tuned\-profiles\-nfv\-guest (7)
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.SH AUTHOR
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.nf
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Jaroslav Škarvada <jskarvad@redhat.com>
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Luiz Capitulino <lcapitulino@redhat.com>
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Andrew Theurer <atheurer@redhat.com>
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