diff options
Diffstat (limited to 'usr/src/man/man4/FSS.4')
| -rw-r--r-- | usr/src/man/man4/FSS.4 | 231 |
1 files changed, 231 insertions, 0 deletions
diff --git a/usr/src/man/man4/FSS.4 b/usr/src/man/man4/FSS.4 new file mode 100644 index 0000000000..33b0136c4f --- /dev/null +++ b/usr/src/man/man4/FSS.4 @@ -0,0 +1,231 @@ +.\" Copyright (c) 2001, Sun Microsystems, Inc. All Rights Reserved +.\" Copyright 2019 Joyent, Inc. +.\" +.\" The contents of this file are subject to the terms of the +.\" Common Development and Distribution License (the "License"). +.\" You may not use this file except in compliance with the License. +.\" +.\" You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE +.\" or http://www.opensolaris.org/os/licensing. +.\" See the License for the specific language governing permissions +.\" and limitations under the License. +.\" +.\" When distributing Covered Code, include this CDDL HEADER in each +.\" file and include the License file at usr/src/OPENSOLARIS.LICENSE. +.\" If applicable, add the following below this CDDL HEADER, with the +.\" fields enclosed by brackets "[]" replaced with your own identifying +.\" information: Portions Copyright [yyyy] [name of copyright owner] +.\" +.Dd December 17, 2019 +.Dt FSS 4 +.Os +.Sh NAME +.Nm FSS +.Nd Fair share scheduler +.Sh DESCRIPTION +The fair share scheduler (FSS) guarantees application performance by explicitly +allocating shares of CPU resources to projects. +A share indicates a project's +entitlement to available CPU resources. +Because shares are meaningful only in +comparison with other project's shares, the absolute quantity of shares is not +important. +Any number that is in proportion with the desired CPU entitlement +can be used. +.Pp +The goals of the FSS scheduler differ from the traditional time-sharing +scheduling class (TS). +In addition to scheduling individual LWPs, the FSS +scheduler schedules projects against each other, making it impossible for any +project to acquire more CPU cycles simply by running more processes +concurrently. +.Pp +A project's entitlement is individually calculated by FSS independently for +each processor set if the project contains processes bound to them. +If a +project is running on more than one processor set, it can have different +entitlements on every set. +A project's entitlement is defined as a ratio +between the number of shares given to a project and the sum of shares of all +active projects running on the same processor set. +An active project is one +that has at least one running or runnable process. +Entitlements are recomputed +whenever any project becomes active or inactive, or whenever the number of +shares is changed. +.Pp +Processor sets represent virtual machines in the FSS scheduling class and +processes are scheduled independently in each processor set. +That is, processes +compete with each other only if they are running on the same processor set. +When a processor set is destroyed, all processes that were bound to it are +moved to the default processor set, which always exists. +Empty processor sets +(that is, sets without processors in them) have no impact on the FSS scheduler +behavior. +.Pp +If a processor set contains a mix of TS/IA and FSS processes, the fairness of +the FSS scheduling class can be compromised because these classes use the same +range of priorities. +Fairness is most significantly affected if processes +running in the TS scheduling class are CPU-intensive and are bound to +processors within the processor set. +As a result, you should avoid having +processes from TS/IA and FSS classes share the same processor set. +RT and FSS +processes use disjoint priority ranges and therefore can share processor sets. +.Pp +As projects execute, their CPU usage is accumulated over time. +The FSS +scheduler periodically decays CPU usages of every project by multiplying it +with a decay factor, ensuring that more recent CPU usage has greater weight +when taken into account for scheduling. +The FSS scheduler continually adjusts +priorities of all processes to make each project's relative CPU usage converge +with its entitlement. +.Pp +While FSS is designed to fairly allocate cycles over a long-term time period, +it is possible that projects will not receive their allocated shares worth of +CPU cycles due to uneven demand. +This makes one-shot, instantaneous analysis of +FSS performance data unreliable. +.Pp +Note that share is not the same as utilization. +A project may be allocated 50% +of the system, although on the average, it uses just 20%. +Shares serve to cap a +project's CPU usage only when there is competition from other projects running +on the same processor set. +When there is no competition, utilization may be +larger than entitlement based on shares. +Allocating a small share to a busy +project slows it down but does not prevent it from completing its work if the +system is not saturated. +.Pp +The configuration of CPU shares is managed by the name server as a property of +the +.Xr project 5 +database. +In the following example, an entry in the +.Pa /etc/project +file sets the number of shares for project +.Sy x-files +to 10: +.Bd -literal -offset 2n +x-files:100::::project.cpu-shares=(privileged,10,none) +.Ed +.Pp +Projects with undefined number of shares are given one share each. +This means +that such projects are treated with equal importance. +Projects with 0 shares +only run when there are no projects with non-zero shares competing for the same +processor set. +The maximum number of shares that can be assigned to one project +is 65535. +.Pp +You can use the +.Xr prctl 1 +command to determine the current share +assignment for a given project: +.Bd -literal -offset 2n +$ prctl -n project.cpu-shares -i project x-files +.Ed +.Pp +or to change the amount of shares if you have root privileges: +.Bd -literal -offset 2n +# prctl -r -n project.cpu-shares -v 5 -i project x-files +.Ed +.Pp +See the +.Xr prctl 1 +man page for additional information on how to modify and +examine resource controls associated with active processes, tasks, or projects +on the system. +See +.Xr resource_controls 7 +for a description of the resource +controls supported in the current release of the Solaris operating system. +.Pp +By default, project +.Sy system +(project ID 0) includes all system daemons +started by initialization scripts and has an +.Dq unlimited +amount of shares. +That +is, it is always scheduled first no matter how many shares are given to other +projects. +.Pp +The following command sets FSS as the default scheduler for the system: +.Bd -literal -offset 2n +# dispadmin -d FSS +.Ed +.Pp +This change will take effect on the next reboot. +Alternatively, you can move +processes from the time-share scheduling class (as well as the special case of +init) into the FSS class without changing your default scheduling class and +rebooting by becoming +.Sy root , +and then using the +.Xr priocntl 1 +command, as shown in the following example: +.Bd -literal -offset 2n +# priocntl -s -c FSS -i class TS +# priocntl -s -c FSS -i pid 1 +.Ed +.Sh CONFIGURING SCHEDULER WITH DISPADMIN +You can use the +.Xr dispadmin 8 +command to examine and tune the FSS +scheduler's time quantum value. +Time quantum is the amount of time that a +thread is allowed to run before it must relinquish the processor. +The following +example dumps the current time quantum for the fair share scheduler: +.Bd -literal -offset 2n +$ dispadmin -g -c FSS + # + # Fair Share Scheduler Configuration + # + RES=1000 + # + # Time Quantum + # + QUANTUM=110 +.Ed +.Pp +The value of the QUANTUM represents some fraction of a second with the +fractional value determined by the reciprocal value of RES. +With the default +value of RES = 1000, the reciprocal of 1000 is \&.001, or milliseconds. +Thus, by +default, the QUANTUM value represents the time quantum in milliseconds. +.Pp +If you change the RES value using +.Xr dispadmin 8 +with the +.Fl r +option, you also change the QUANTUM value. +For example, instead of quantum of 110 with RES +of 1000, a quantum of 11 with a RES of 100 results. +The fractional unit is different while the amount of time is the same. +.Pp +You can use the +.Fl s +option to change the time quantum value. +Note that such changes are not preserved across reboot. +Please refer to the +.Xr dispadmin 8 +man page for additional information. +.Sh SEE ALSO +.Xr prctl 1 , +.Xr priocntl 1 , +.Xr priocntl 2 , +.Xr project 5 , +.Xr resource_controls 7 , +.Xr dispadmin 8 , +.Xr psrset 8 +.Pp +.%T System Administration Guide: Virtualization Using the Solaris Operating System |