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: [email protected]
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: [email protected]
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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