Alan, I would assume that if you need that 64 bit addressing (not 64 bit
arithmetic, which has been around a long time), you want to use a LOT of
memory. VM gets along by running a lot of images by sharing memory and
paging the excess, which is the basis for most of the discussion on this
board. If you really NEED a lot of memory, then you have to go to LPAR to
effectively use it. If you app is truly 64 bit and needs 5-10 GB of real
memory, running it under VM will impair its performance.
This issue is when you need to start think about dedicated LPARs for large
apps. We regulary swamp a 32 GB zSeries VM with some of our Linux machines,
so we have to move them to LPARs to get the throughput that we need.
It seems to me, as an approximation, that 99% of the work being done on
Linux is on Intel; 0 .99% on VM guests, and .01% on LPARS, the area I work
in most. My answers tend to be skewed to a the very small population of
very big apps.
Regards, Jim
Linux S/390-zSeries Support, SEEL, IBM Silicon Valley Labs
t/l 543-4021, 408-463-4021, [EMAIL PROTECTED]
*** Grace Happens ***
Alan
Altmark/Endicott/ To: [EMAIL PROTECTED]
[EMAIL PROTECTED] cc:
Sent by: Linux on Subject: Re: Probly a stoopid ?,
but what's "better"...31-bit or 64-bit?
390 Port
<[EMAIL PROTECTED]
IST.EDU>
07/14/2003 09:38
AM
Please respond to
Linux on 390 Port
On Monday, 07/14/2003 at 09:14 MST, Jim Sibley/San Jose/[EMAIL PROTECTED] wrote:
> However, some apps now are being written assuming 64 bit. You can
develop
> them in 64bit on in an guest environment, but to get their full power,
you
> need to run them in an LPAR.
I'm sorry, Jim, but I don't understand this comment. Any application, on
any platform, 31-bit or 64-bit, requires dedication of resources to get
"full power" from the application. The more resources you give it, the
"better" it runs. True of PCs. True of LPARs. True of guests on z/VM.
I will not argue that sometimes the level of "better" you are looking for
(after considering the price/performance trade-offs) may come only from
LPAR, but I maintain that's not a characteristic particular only to 64-bit
apps.
Alan Altmark
Sr. Software Engineer
IBM z/VM Development
