Adrian,
1. Can we up the number of CPU cores emulated - I know the answer if yes but will VM/370 use it? Do we need to change CP settings, and how? I suggest we try and target 4 given the state of typical PC/Server/Container configurations. I appreciate VM/370 (ans specifically CMS) might not be getting too much benefit but hey why not press the Sport button anyway!
VM/370 does support 2 CPUs in the configuration as an attached processor (called AP-mode).? However, it is of limited value, especially in a single-user environment that most of us have when running under Hercules.? The second processor cannot do any i/o.? Timing tests under Hercules have shown that things run slower in AP-mode due to the overhead of CP managing the second processor (who gets dispatched on it, maintaining dual sets of user page tables, and rescheduling i/o operations back to the main processor).? In a real multi-user system that was common back in the day, AP-mode probably provided benefits because there was enough CPU-bound activity that the attached processor could capitalize on.
Further, when in AP-mode, ECPS:VM must be turned off.
By far the largest benefit and biggest-bang-for-the-buck would be to turn on ECPS:VM? (ECPSVM YES in your Hercules configuration).? The benefit here is way better than anything AP-mode will provide.? A couple of important bugs were fixed in ECPS:VM Hercules support in Hercules 3.13, and if you are running any of the Hyperion releases ECPS:VM support was enhanced to provide even greater benefits.
2. Can we provide more S/370 Storage (i.e. RAM). Appreciate the 24bit limit but does VM370 support any paging memory devices? Assume some CP configuration, if this is possible at all?
No.? Nothing in this area is available.
3. What DASD device does the Six Pack configuration use for paging? Can we isolate this feature to one appropriately sized DASD device? Because if we did we could run it uncompressed, no shadow, and on a RAM disk. If it was an appropriate size (50-100MB) we could run it in non-pageable linux RAM for maximum performance, if it was bigger we would probably be obliged to put it in pageable RAM.
In VM/370, the paging space and the spool space are shared.? In SixPack, this is 3350 devices.? If one wanted, you could certainly format an empty 3350 or a 3380 (if running Sixpack 1.3) volume and have a dedicated page/spool volume, and make that uncompressed and so forth.? You'd have to remove the page/spool space on the other Sixpack volumes by using the format/allocate program.? This would need to be done with some care.
If you are having a lot of paging, the best thing would be to try to reduce it rather than come up with a scheme to page faster.? The fastest page i/o is the one you never do.? Reduce dependency on high level languages which produce huge working sets and large module sizes (especially from compilers back in the day).? Write more assembler code.? Don't logon extra virtual machines that you might not be using, e.g., CPWATCH, RSCS, etc.
4. I note that the change log for Six Pack supports new DASD devices? Is there an optimisation opportunity here?
I can't see how, other than the possibility mentioned above of using a dedicated 3380 device for paging and spooling and making it uncompressed dasd in Hercules.? I'm personally skeptical that this would provide more than a scant 1-2% improvement, but that is just a gut feel and I have no hard numbers to back it up.? I just don't think it is worth the trouble for what little would be gained.
Regards,
Bob
