So, you are saying that 5x1 does not equal 5?
-----Original Message-----
From: The IBM z/VM Operating System
[mailto:[EMAIL PROTECTED] On Behalf Of Marty Zimelis
Sent: Friday, March 23, 2007 3:16 PM
To: [email protected]
Subject: Re: CPU usage -- virtual or dedicated ?
You are misinterpreting the usage note. What it means is that
relative shares are doled out as integers. In other words, while a
virtual machine's relative share is normally divided equally amongst its
vCPUs, when you get to the case where the number of those vCPUs exceeds
the total relative share assigned to the user, each vCPU gets a minimum
relative share of 1.
Marty
____________________
Martin Zimelis
Principal
maz/Consultancy
_____
From: The IBM z/VM Operating System
[mailto:[EMAIL PROTECTED] On Behalf Of Stracka, James (GTI)
Sent: Friday, March 23, 2007 3:06 PM
To: [email protected]
Subject: Re: CPU usage -- virtual or dedicated ?
That seems to be the opposite of what USAGE NOTE 6
states for HELP CPSE SHARE:
"When setting SHARE RELATIVE on a userid that has
multiple CPUs, the
minimum share that the system will assign is one per
virtual CPU. For
example, if you SET SHARE MAINT RELATIVE 1 and MAINT has
five virtual
CPUs, the resulting SHARE will be set to five."
By the above, setting RELATIVE 100 with 2 CPUs you get
an effective RELATIVE 200.
-----Original Message-----
From: The IBM z/VM Operating System
[mailto:[EMAIL PROTECTED] On Behalf Of Schuh, Richard
Sent: Friday, March 23, 2007 2:59 PM
To: [email protected]
Subject: Re: CPU usage -- virtual or dedicated ?
The Relative 100 applies to the overall virtual
machine. If you define each with 2 cpus, each cpu would be competing at
a Relative 50 when the system is busy. That may be an inhibiting factor.
With our TPF systems, each normally running with 3 CPUs - sometimes
more, sometimes fewer, we multiply the number of cpus by 100 to arrive
at a relative share value for the virtual machine. This seems to solve a
lot of slowdown issues that our testers encounter.
Regards,
Richard Schuh
_____
From: The IBM z/VM Operating System
[mailto:[EMAIL PROTECTED] On Behalf Of Kris Buelens
Sent: Friday, March 23, 2007 11:41 AM
To: [email protected]
Subject: Re: CPU usage -- virtual or dedicated ?
As the first share setting is "REL 100" they get
the same priority as any other VM user that wants to run.
So, if you want to give them a favor you should
e.g. set the first share to REL 1000, or maybe ABS 30%
2007/3/23, Stracka, James (GTI)
<[EMAIL PROTECTED]>:
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?
--
Kris Buelens,
IBM Belgium, VM customer support
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