Re: Performance under z/VM 5.1

[McKown, John]

Title: Message

I think I found the answer:

 

<quote>

 Finally, zSeries hardware supports only up to two levels of SIE. When z/VM runs in basic mode (no LPARs), the first-level z/VM uses one level of SIE to dispatch its guests, leaving one level of SIE available for a second-level V=R or V=F z/VM to dispatch its guests. Thus VSE-on-VM-on-VM runs well (no performance impact) in basic mode when preferred guest support is used. This can only be done on a system prior to z/VM 5.1.0. However, when z/VM runs in an LPAR, the LPAR hypervisor uses one level of SIE to dispatch z/VM, and z/VM uses the second level of SIE to dispatch its guest. Thus VSE-on-VM-on-VM in an LPAR is a poor performer, because hardware support of SIE runs out after two levels. z/VM has to simulate the third level of SIE.

</quote>

 

From http://www.vm.ibm.com/perf/tips/z890.html

 

but this is talking about a z890, not a z800. It appears that a z800 can run in BASIC mode. But notice the sentence in red.

 

 

--
John McKown
Senior Systems Programmer
HealthMarkets
Keeping the Promise of Affordable Coverage
Administrative Services Group
Information Technology

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-----Original Message-----
From: The IBM z/VM Operating System [mailto:[EMAIL PROTECTED] On Behalf Of Wakser, David
Sent: Friday, July 28, 2006 10:48 AM
To: IBMVM@LISTSERV.UARK.EDU
Subject: Re: Performance under z/VM 5.1

John:
 
    You have asked the correct question, since I am pretty certain that the SIE is the problem (older VMs had 3, and that was reduced). Any answers to the question: will replacing a single LPAR running z/VM (and 2nd level z/VMs with 3rd level guests) have any advantage?

David Wakser

________________________________

From: McKown, John [mailto:[EMAIL PROTECTED]]
Sent: Friday, July 28, 2006 11:30 AM
To: IBMVM@LISTSERV.UARK.EDU
Subject: Re: Performance under z/VM 5.1

David,
 
I hope some others will chime in, but I'm not sure that moving to LPAR will really help. I assume you will run the clients' z/VM systems each in their own LPAR instead of under your current z/VM. Were you aware that LPAR is, in fact, a sort-of VM and was originally based on VM? The reason that I ask this is because your 3r level guests (z/VSE) are likely getting rotten response due to the fact that the SIE (which reduces z/VM overhead significantly) only goes two levels deep (IIRC). When you replace the current "master" z/VM with LPAR, the LPAR hypervisor will still "use up" one of those SIE levels. So I'm fairly sure that simply replacine a "master" z/VM on a z800 in BASIC mode with an LPAR setup will not really help very much.

Question to the audience: Can a z800 run in BASIC mode? Or was that the first machine which did away with BASIC mode? If a z800 does not have BASIC mode, then will replacing a single LPAR running z/VM (and 2nd level z/VMs with 3rd level guests) have any advantage.

 

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