Hi,
while there are regular builds in queue jenkins uses around 10-20% CPU, but when there are builds blocked by throttle concurrent builds plugin, then CPU goes to 200-400% and website is very slow.

System Properties
Name ↓

Value
awt.toolkit sun.awt.X11.XToolkit
executable-war /usr/share/jenkins/jenkins.war
file.encoding UTF-8
file.encoding.pkg sun.io
file.separator /
hudson.diyChunking true
java.awt.graphicsenv sun.awt.X11GraphicsEnvironment
java.awt.headless true
java.awt.printerjob sun.print.PSPrinterJob
java.class.path /usr/share/jenkins/jenkins.war
java.class.version 52.0
java.endorsed.dirs /usr/lib/jvm/java-8-oracle/jre/lib/endorsed
java.ext.dirs /usr/lib/jvm/java-8-oracle/jre/lib/ext:/usr/java/packages/lib/ext
java.home /usr/lib/jvm/java-8-oracle/jre
java.io.tmpdir /tmp
java.library.path /usr/java/packages/lib/amd64:/usr/lib64:/lib64:/lib:/usr/lib
java.runtime.name Java(TM) SE Runtime Environment
java.runtime.version 1.8.0_66-b17
java.specification.name Java Platform API Specification
java.specification.vendor Oracle Corporation
java.specification.version 1.8
java.vendor Oracle Corporation
java.vendor.url http://java.oracle.com/
java.vendor.url.bug http://bugreport.sun.com/bugreport/
java.version 1.8.0_66
java.vm.info mixed mode
java.vm.name Java HotSpot(TM) 64-Bit Server VM
java.vm.specification.name Java Virtual Machine Specification
java.vm.specification.vendor Oracle Corporation
java.vm.specification.version 1.8
java.vm.vendor Oracle Corporation
java.vm.version 25.66-b17
javamelody.About Monitoring https://wiki.jenkins-ci.org/display/JENKINS/Monitoring
javamelody.analytics-id UA-1335263-7
javamelody.custom-reports Jenkins Info,About Monitoring
javamelody.gzip-compression-disabled true
javamelody.http-transform-pattern /\d+/|/site/.|avadoc/.|/ws/.|obertura/.|estReport/.|iolations/file/.|/user/.|/static/\w/|/adjuncts/\w+/|/bound/[\w\-]+
javamelody.Jenkins Info /systemInfo
javamelody.no-database true
javamelody.storage-directory //var/lib/jenkins/monitoring
javamelody.system-actions-enabled true
jcifs.smb.client.domain JIDomain
jna.platform.library.path /usr/lib/x86_64-linux-gnu:/lib/x86_64-linux-gnu:/lib64:/usr/lib:/lib
jnidispatch.path /tmp/jna--1712433994/jna3512835223512613503.tmp
lib.svnkit.http.methods Digest,Basic,NTLM,Negotiate
lib.svnkit.ssh2.persistent false
line.separator
mail.smtp.sendpartial true
mail.smtps.sendpartial true
os.arch amd64
os.name Linux
os.version 3.13.0-24-generic
path.separator :
pid 26197
sun.arch.data.model 64
sun.boot.class.path /usr/lib/jvm/java-8-oracle/jre/lib/resources.jar:/usr/lib/jvm/java-8-oracle/jre/lib/rt.jar:/usr/lib/jvm/java-8-oracle/jre/lib/sunrsasign.jar:/usr/lib/jvm/java-8-oracle/jre/lib/jsse.jar:/usr/lib/jvm/java-8-oracle/jre/lib/jce.jar:/usr/lib/jvm/java-8-oracle/jre/lib/charsets.jar:/usr/lib/jvm/java-8-oracle/jre/lib/jfr.jar:/usr/lib/jvm/java-8-oracle/jre/classes
sun.boot.library.path /usr/lib/jvm/java-8-oracle/jre/lib/amd64
sun.cpu.endian little
sun.cpu.isalist
sun.font.fontmanager sun.awt.X11FontManager
sun.io.unicode.encoding UnicodeLittle
sun.java.command /usr/share/jenkins/jenkins.war --accessLoggerClassName=winstone.accesslog.SimpleAccessLogger --simpleAccessLogger.format=combined --simpleAccessLogger.file=/var/log/jenkins/access.log --webroot=/var/cache/jenkins/war --httpPort=-1 --ajp13Port=-1 --httpsPort=8080 --httpsKeyStore=/etc/ssl/private/pol-compile-1.keystore --httpsKeyStorePassword=unwcdwawmsct
sun.java.launcher SUN_STANDARD
sun.jnu.encoding UTF-8
sun.management.compiler HotSpot 64-Bit Tiered Compilers
sun.os.patch.level unknown
user.country US
user.dir /
user.home /var/lib/jenkins
user.language en
user.name jenkins
user.timezone Europe/Warsaw
Environment Variables
Name ↓

Value
_ /usr/bin/daemon
HOME /var/lib/jenkins
JENKINS_HOME /var/lib/jenkins
LANG en_US.UTF-8
LANGUAGE en_US:en
LOGNAME jenkins
MAIL /var/mail/jenkins
NLSPATH /usr/dt/lib/nls/msg/%L/%N.cat
PATH /usr/local/bin:/usr/bin:/bin:/usr/local/games:/usr/games
PWD /var/lib/jenkins
QT_GRAPHICSSYSTEM native
SHELL /bin/bash
SHLVL 1
TERM xterm
USER jenkins
XDG_RUNTIME_DIR /run/user/1033
XDG_SESSION_ID 1942
XFILESEARCHPATH /usr/dt/app-defaults/%L/Dt
Plugins
Name ↓

Version

Enabled

Pinned
active-directory 1.41 true false
ansicolor 0.4.1 true false
ant 1.2 true false
antisamy-markup-formatter 1.3 true true
artifactdeployer 0.33 true false
backup 1.6.1 true false
build-blocker-plugin 1.6 true false
build-flow-plugin 0.18 true false
build-flow-test-aggregator 1.1 true false
build-monitor-plugin 1.6+build.149 true false
build-name-setter 1.3 true false
build-pipeline-plugin 1.4.7 true false
build-timeout 1.14.1 true false
buildgraph-view 1.1.1 true false
buildresult-trigger 0.17 true false
categorized-view 1.8 true false
claim 2.7 true false
cloudbees-credentials 3.3 true false
compact-columns 1.10 true false
conditional-buildstep 1.3.3 true false
credentials 1.22 true true
cvs 2.12 true true
cvs-tag 1.7 true false
dashboard-view 2.9.6 true false
delivery-pipeline-plugin 0.9.4 true false
email-ext 2.40.5 true false
email-ext-recipients-column 1.0 true false
emailext-template 0.4 true false
envinject 1.91.3 true false
environment-script 1.2.2 true false
external-monitor-job 1.4 true true
files-found-trigger 1.3.1 true false
fstrigger 0.39 true false
git-client 1.19.0 true false
git-server 1.6 true false
global-post-script 1.0.12 true false
heavy-job 1.1 true false
instant-messaging 1.35 true false
ircbot 2.26 true false
ivytrigger 0.34 true false
javadoc 1.3 true true
jenkins-multijob-plugin 1.16 true false
jenkinswalldisplay 0.6.30 true false
job-restrictions 0.4 true false
jquery 1.11.2-0 true false
jquery-ui 1.0.2 true false
junit 1.6 true true
ldap 1.11 true true
leastload 1.0.3 true false
locks-and-latches 0.6 true false
mailer 1.15 true true
mapdb-api 1.0.6.0 true false
matrix-auth 1.2 true true
matrix-project 1.6 true true
maven-plugin 2.10 true true
measurement-plots 0.1 true false
monitoring 1.59.0 true false
naginator 1.16.1 true false
nested-view 1.14 true false
nodelabelparameter 1.5.1 true false
pam-auth 1.2 true true
parameterized-trigger 2.27 true false
periodicbackup 1.3 true false
plain-credentials 1.1 true false
postbuild-task 1.8 true false
powershell 1.3 true false
PrioritySorter 3.4 true false
project-inheritance 1.5.3 true false
publish-over-ssh 1.13 true false
pwauth 0.4 true false
ruby 1.2 true false
ruby-runtime 0.12 true false
rubymotion 1.11 true false
run-condition 1.0 true false
rvm 0.4 true false
scm-api 0.2 true false
scp 1.8 true false
script-security 1.14 true true
scriptler 2.9 true false
scripttrigger 0.31 true false
selenium-builder 1.14 true false
sidebar-link 1.7 true false
simple-theme-plugin 0.3 true false
ssh 2.4 true false
ssh-agent 1.7 true false
ssh-credentials 1.11 true true
ssh-slaves 1.9 true true
subversion 2.5 true true
summary_report 1.13 true false
terminate-ssh-processes-plugin 1.0 true false
test-stability 1.0 true false
thinBackup 1.7.4 true false
throttle-concurrents 1.8.4 true false
timestamper 1.6.2 true false
token-macro 1.11 true false
translation 1.12 true true
urltrigger 0.38 true false
versionnumber 1.5 true false
view-job-filters 1.26 true false
vsphere-cloud 2.5 true false
windows-slaves 1.1 true true
xfpanel 1.2.3 true false
xshell 0.10 true false
xtrigger 0.54 true false
xvfb 1.0.16 true false
xvnc 1.22 true false