[THIN] KB:CTX106021 - FAQ: The CPU Utilization Management Feature
- From: "Jim Kenzig http://thethin.net" <jimkenz@xxxxxxxxxxxxxx>
- To: thin@xxxxxxxxxxxxx
- Date: Thu, 19 May 2005 18:41:05 -0700 (PDT)
CTX106021 - FAQ: The CPU Utilization Management Feature
This document was published at:
http://support.citrix.com/kb/entry.jspa?externalID=CTX106021
Document ID: CTX106021, Created on: Apr 22, 2005, Updated: May 17, 2005
Products: Citrix Presentation Server 4.0 for Microsoft Windows 2000, Citrix
Presentation Server 4.0 for Microsoft Windows 2003
Summary
CPU Utilization Management is a new feature introduced with Citrix Presentation
Server 4.0. This FAQ article covers the feature in depth.
Q: What is the CPU Utilization Management feature designed to do?
It is a feature of Presentation Server 4.0 designed to give each user a fair
share of the CPU by modifying the normal job priority scheduling in the
operating system. CPU time will be allocated fairly across all users on the
server. It normalizes the CPU usage of each user by smoothing out the normal
CPU peaks that most applications have. It will limit very CPU-intensive
applications to a fair-share of the CPU, so that one user does not
inadvertently have an inappropriate adverse affect on the other users. This
enables administrators to easily calculate how many users can fit on a machine
at once and hence how many machines must be purchased.
Q: What is a Share?
A Share is a relative percentage of the CPU that each user receives. By default
each user is assigned 8 shares. The percentage of CPU time that a user gets is
relative because it is dependent on the number of users that are logged into a
particular server. For example, if there are 4 users logged into a system and
each user has 8 equal shares, that means each user receives 25% of the CPU. If
there are 10 users logged on, each user receives 10%. This is a ?soft limit?,
and if the user is not using all of their CPU time, other users can borrow it.
Likewise, it can borrow from other users as well if needed and if CPU time is
available.
Q: What is a Reservation?
A CPU reservation sets aside a specific percentage of the CPU that will always
be made available to the user if needed. This is a ?soft limit? and if the user
is not using all of their CPU time other users can borrow it. By default 20% of
the CPU has been set aside for the System Context which leaves the remaining
80% to be divided into shares.
Q: What Edition of Presentation Server supports this feature?
Citrix Presentation Server 4.0 Enterprise Edition and an Enterprise Edition
license file must be on the license server.
Q: How does the CPU Utilization Management feature work?
It is enabled in the Presentation Server Console in the farm or server
properties under Memory/CPU Utilization Management. Once the feature is enable
the ?Citrix CPU Utilization Mgmt/Resource Mgmt? service and the ?Citrix CPU
Utilization Mgmt/User-Session Sync? service start up. The ?Citrix CPU
Utilization Mgmt/Resource Mgmt? service does the following: it monitors users
and processes, calculates load, and makes OS calls to set the CPU priority of
processes. The ?Citrix CPU Utilization Mgmt/User-Session Sync? ensures that all
processes associated with a user?s session get associated with that user when
determining load. This service is necessary to keep track of processes that
normally run under the system context such as CSRSS.exe and winlog.exe, and to
make sure that they are reported under the correct user session for load
calculation.
Q: How can I verify how much CPU each user is using?
You can use Performance Monitor to see the Average CPU usage for each user
session. There is a new Performance Monitor object called ?Citrix CPU
Utilization Mgmt User? with five specific counters called CPU Entitlement, CPU
Reservations, CPU Shares, CPU Usage, Long term CPU Usage that should help an
administrator verify the functionality of the feature. You can also use the CPU
Optimization Report in the Report Center in the Access Suite Console to create
a report detailing CPU Usage per user. This report does require a connection to
a Resource Manager Summary database.
Q: Can I assign more CPU Shares or create a Reservation for a user?
Yes. The default share for each user is 8 and a default reservation of 20% has
been set aside for the System Context. Modifying the default values is not
necessary however if an administrator chooses to do so they can go to
HKEY_LOCAL_MACHINE\SOFTWARE\Citrix\CTXCPU <Policy>.
To assign a user a specific number of shares under the <Policy> value add:
Domain\u1,cpu.shares=# (where # represents the number of shares to be
assigned).
To create a reservation for a user under the <Policy> value add:
Domain\u2,cpu.reservation=# (where # represents the percentage in thousands.
For example, 10%=10000).
Once changes have been made to the CTXCPU key in the registry, for the changes
to take effect, restart the ?Citrix CPU Utilization Mgmt/Resource Mgmt? and the
?Citrix CPU Utilization Mgmt/User-Session Sync? services. To verify that the
changes are in effect, use Performance Monitor with the object and counters
specified above.
When modifying the registry key the format is very important. The user name has
to be written domain name or the server name\username. Shares can only fall in
the range from 1-64. A reservation?s percentage is represented in thousands.
The maximum value that can be assigned for a reservation equals the number of
processors in the server. For example, a quad processor machine would have a
maximum value of 400,000. An administrator needs to do their own base line
testing to find out what numbers would achieve the required performance.
Q: Can I assign more CPU Shares or Reservations to a group?
No. You can only assign shares and reservations to users not groups.
Q: Can I assign Shares or Reservations for applications?
No, not with this feature. You can use the CPU prioritization setting in the
properties of each published application to set the application?s CPU priority
level to Above Normal, Below Normal, and so on.
Q: Are the services ?Citrix CPU Utilization Mgmt/Resource Mgmt? and ?Citrix
CPU Utilization Mgmt/User-Session Sync? dependent on the IMA service?
Yes. Both services are stopped and started by the IMA service once the feature
is enabled or disabled. When looking at the properties of the services in the
Services Manager you will see that they are set to manual because they are
controlled by the IMA service. However if the IMA service fails to start then
both services will not be automatically started but they can be started
manually. Restarting the IMA service does not restart either of the two
services.
Q: Is there a list of applications that are incompatible with this feature?
No. All applications should function with this feature
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