Re: How does VM user enter Q0 list besides SET QUICKDSP ON
Lockshot refers to making a virtual processor temporarily class 0 if it is holding a critical z/VM Control Program resource, typically a system lock. Since most system locks of that nature are held for very short periods of time, it isn't very common. Hotshot refers to making a virtual processor temporarily class 0 due to certain interactions (issuing CP command). It's very short lived and doesn't really allow the virtual machine a long term advantage. I seem to recall, that when going back to eligible list after a hotshot, there is a small penalty, but not positive. Some of this shows up in monitor data. Or in the INDICATE QUEUES EXP command. Normally, I'd look something like the following from the command: BITNERQ1 R00 2531/2510 .I.. -.1308 A00 The first character of the cryptic 4 characters after the estimated working set size is the key. It will be an 'L' for LOCKSHOT and 'H' for 'HOTSHOT': BITNERQ0 R00 2531/2510 LI.. -.1308 A00 BITNERQ0 R00 2531/2510 HI.. -.1308 A00 I also remembered there is a fourth case that the virtual machine is treated as Class 0. When the virtual machine is in process of logging off, it is treated like class 0 as there is no reason to delay it freeing up resources. Bill Bitner - z/VM Customer Focus and Care - IBM Endicott - 607-429-3286
Re: How does VM user enter Q0 list besides SET QUICKDSP ON
What Q0 mainly does is keeps a VMDBK out of the eligible list. SET QUICK DSP is the only externally available way of getting a guest into Q0. Hot-sho t and lock-shot are internal settings that indicate to the scheduler that t his VMDBK should not be delayed for some reason. For example, lock-shot mean s the VMDBK holds some lock and so we don't want to hold dispatch of that VMDBK up in the eligible list since there might be other threads queued u p on the lock waiting for this one to release it. If that would happen, al l of those other threads would be hung up until the one holding the lock ge ts out of e-list limbo. Similarly, hot-shot gives the user a brief boost because the user interacted with its terminal and we want to give the interactive user a little preference. We don't want the user in the eligible list during this brief boost. Mark Lorenc CP Development
How does VM user enter Q0 list besides SET QUICKDSP ON
Hello, When I read VM Performance book, I was confused by a few terms regards Q0 list. There are three conditions can enter Q0 list: QUICKDSP, hot-shot, lock-shot. What does hot-shot/lock-shot mean? What kind of situation would be considered as hot-shot/lock-shot? Can CP set hot-shot/lock-shot on by commands? If yes, how? Are there any real cases (such as DB2...) relevant to hot-shot/lock-shot? Thanks in advance. Regards, Changer
