Only if the guest can handle it. CMS runs in a single CPU but VSE,
OS/390, z/Linux, TPF, VM and others that can run on multiple CPUs can.
-----Original Message-----
From: The IBM z/VM Operating System
[mailto:[EMAIL PROTECTED] On Behalf Of Huegel, Thomas
Sent: Friday, March 23, 2007 2:53 PM
To: [email protected]
Subject: Re: CPU usage -- virtual or dedicated ?
I don't use the share settings as you suggested I have 7 full
production VSE's and use VM Resource Manager to dynamically change the
share settings as the workloads change. This seems to work very well.
But I don't seem to totally understand is what advantages (or
disadvantages) there are to giving the VSE's multiple virtual CPU's. I
seem to remember some discussion that z/LINUX will eat up as many cpu's
as it can get.. and one must be carefull.
Does VM really dispatch the guest on more than one processor?
Just how does it work?
-----Original Message-----
From: The IBM z/VM Operating System
[mailto:[EMAIL PROTECTED]
Behalf Of Stracka, James (GTI)
Sent: Friday, March 23, 2007 1:18 PM
To: [email protected]
Subject: Re: CPU usage -- virtual or dedicated ?
I am not in favor of dedicating virtual CPUs as this restricts
the other
users of the system and is a potential waste of resources and
money.
Since the CP Scheduler does an excellent job of distribution of
the
resources, then using the SHARE command might be better.
Assuming there are more than two VSE machines of which two
really need
to use two virtual CPUs each and there are four real CPUs, then
if I am
correct issue two SET SHARE commands:
set share vseguest1 relative 100 absolute 49% limithard
set share vseguest2 relative 100 absolute 49% limithard
Okay, it could be absolute 50% but if both VSE guests wanted the
maximum
resources at the same time, no other work would get done.
My understanding of those two commands is that they would allow
either
VSE guest to get almost the full usage of two real CPUs each any
time
they need them. Stated another way, either could at most get
49% of the
box leaving the remaining 51% for all the other users of the
four CPUs.
If both wanted the maximum at the same time it would be 49% for
vseguest1, 49% for vseguest2 and 2% for the remaining users.
Any other
time, the workload would be spread evenly among all the guests
in the
box given QUICKDSP and other SHARE settings.
Am I correct?
-----Original Message-----
From: The IBM z/VM Operating System
[mailto:[EMAIL PROTECTED] On
Behalf Of Stephen Frazier
Sent: Friday, March 23, 2007 11:40 AM
To: [email protected]
Subject: Re: CPU usage -- virtual or dedicated ?
Many VSE shops have been running on multiple processors for a
long time.
We first started it on the
4381. Adding virtual processors to VSE improves performance but
not as
much as most people expect.
With 2 processors you get about 180% of one processor. With 3
processors
you get about 240%. More
than 3 processors gives very little if any improvement. I have
not found
that dedicating a processor
to VSE does any good. Others have done it.
My recommendation with several processors. Define multiple VSE
guests
and divide the workload among
them. Give each guest 2 virtual processors. Let VM decide how to
dispatch the virtual processors on
the real processors.
These recommendations assume any VSE after about VSE/ESA 2.4
using the
turbo dispatcher and a VM
after HPO. :)
Posted to both VM-L and VSE-L.
[EMAIL PROTECTED] wrote:
> I picked this up from the VSE-L, but it is a good question for
VM. I
> think many VSE shops are seeing multiple processors for the
first time
> when they move to z-hardware and under VM it can be confussing
as what
> to do with 4 processors.
>
> The question(s) arise.
> 1) Is anything gained by giving VSE more than 1 virtual CPU?
> 2) With only 4 to go around does dedicating processors to VSE
make
> sense?
> 3) Would the answers be any different depending on the number
of guest
VSE?
>
> Assume z/VM 5.2 and z/VSE 3.1
>
> Thanks
--
Stephen Frazier
Information Technology Unit
Oklahoma Department of Corrections
3400 Martin Luther King
Oklahoma City, Ok, 73111-4298
Tel.: (405) 425-2549
Fax: (405) 425-2554
Pager: (405) 690-1828
email: stevef%doc.state.ok.us
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