Very few people understand the scheduler, and what it does - What it
does, it does very well. You just have to understand the language.
Rob did some recent experiments that validated how it works, and
validated how little functions like VRM really help your workloads
(except by accident). From the VelocitySoftware.com page, go to "Linux
Hints and Tips". There is a new link there to Rob's recent research. I
would recommend reading it and understanding it before setting shares
(or using VRM).
Hughes, Jim wrote:
Thanks for the reply Marty. Long time, no see.
Our VSE systems are mainly interactive CICS or IDMS/DC systems during
the day. Night time they become batch machines.
The CICS and IDMS/DC systems are mainly accessed via VTAM.
Our three production systems are each set to ABSOLUTE 20% with no
defined target maximum. The sum of our ABSOLUTE SHARE users does total 100%.
With that said, we’ve asked ourselves is ABSOLUTE 20% enough?
The manual says once you have defined the minimum target ABSOLUTE SHARE
to total 100%, the scheduler reserves 1% for the RELATIVE SHARE users.
It goes on to say that once an ABSOLUTE SHARE user has reached its
minimum target share it only gets more if system resources are available.
What I am looking for is a way to keep the production systems behaving
if a production vse system(absolute share), test vse system(relative
share) or a cms user(relative share) begins to loop.
The more I read about CP SET SHARE the more I suspect it isn’t designed
to be a panacea for smooth performance in time of trouble.
Maybe I should be investigating the VM Performance Monitor to assist
with dynamic performance adjustment in a time of trouble. Comments?
____________________
Jim Hughes
Consulting Systems Programmer
Mainframe Technical Support Group
Department of Information Technology
State of New Hampshire
27 Hazen Drive
Concord, NH 03301
603-271-5586 Fax 603.271.1516
Statement of Confidentiality: The contents of this message are
confidential. Any unauthorized disclosure, reproduction, use or
dissemination (either whole or in part) is prohibited. If you are not
the intended recipient of this message, please notify the sender
immediately and delete the message from your system.
------------------------------------------------------------------------
*From:* The IBM z/VM Operating System [mailto:IBMVM@LISTSERV.UARK.EDU]
*On Behalf Of *Martin Zimelis
*Sent:* Monday, February 07, 2011 3:01 PM
*To:* IBMVM@LISTSERV.UARK.EDU
*Subject:* Re: SET SHARE ABSOLUTE/RELATIVE
Catherine,
I don't think your understanding of SHARE is backwards, but your
expectation of what the performance manager will do might be. I suspect
it's trying to keep heavy CPU users from hogging the processors.
To get back to the original question, Jim, I think you need to
describe what the z/VSE guests are doing. If they're supporting
interactive users (e.g., CICS), you'd want one answer from the assembled
masses. If they're true batch workloads, the answer should be quite
different. Since your system's perceived responsiveness likely depends
on how quickly TCPIP (and VTAM) gets serviced, a high share is called
for. In your situation, is the same true for RSCS? Regardless, my
experience with the conventional wisdom of whether to use relative or
absolute shares is dated, so I'll leave detailed recommendations to
those with more recent experience.
Marty Zimelis
On Mon, Feb 7, 2011 at 2:13 PM, McBride, Catherine <cmcbr...@kable.com
<mailto:cmcbr...@kable.com>> wrote:
A while ago a very experienced VM person from IBM suggested that we not
use ABSOLUTE unless you "absolutely" must cap off a guest to keep it
from running away with your real processors. We used that setting on
our test system only.
Our VSE TOR and VM guest TCPIP both had high relative shares (10000
versus 3000 for regular production guests).
Then we started using a performance manager feature of VM Toolkit, it
managed share values for us.
It set everything the same after VM IPL, but by the end of a normal
production day our busiest guests had dropped to the lowest relative
share, the ones seldom used had the highest. Meaning my understanding
of how relative share worked was backwards or the gizmo in VM Toolkit
was. Hopefully Alan or Kris will expound.
-----Original Message-----
From: The IBM z/VM Operating System [mailto:IBMVM@LISTSERV.UARK.EDU
<mailto:IBMVM@LISTSERV.UARK.EDU>] On
Behalf Of Hughes, Jim
Sent: Monday, February 07, 2011 12:57 PM
To: IBMVM@LISTSERV.UARK.EDU <mailto:IBMVM@LISTSERV.UARK.EDU>
Subject: SET SHARE ABSOLUTE/RELATIVE
I've read the CP COMMAND manual and the PERFORMANCE manual regarding the
SET SHARE command and how it works.
Would someone care to comment on how you have used them for your z/VSE
production and guest machines?
What would suggest for TCPIP/RSCS/VTAM SET SHARE values?
Thanks in advance.
____________________
Jim Hughes
Consulting Systems Programmer
Mainframe Technical Support Group
Department of Information Technology
State of New Hampshire
27 Hazen Drive
Concord, NH 03301
603-271-5586 Fax 603.271.1516
Statement of Confidentiality: The contents of this message are
confidential. Any unauthorized disclosure, reproduction, use or
dissemination (either whole or in part) is prohibited. If you are not
the intended recipient of this message, please notify the sender
immediately and delete the message from your system.
