Determining processor status without IPIs 726

glen herrmannsfeldt

page fault handshaking ... where vm would try to reflect to vs1 operating system that vm was handling for the vs1 virtual machine ... under the buttumption that the fault might be for a specific task (in the vs1 multi-tasking environment) ... allowing vs1 a chance to switch tasks.

it had been done along with ecps for virgil-tully ... an endicott effort for the 138-148 ... attempting to make the environment nearly "vm only" ... i.e. customers would never run the machines in a non-vm environment ... something akin to the current proliferation of LPAR production environments in customer shops. misc. past posts about microcode related enhancements

the idea had originally been done earlier for cp67 and mvt

from melinda's history of vm

from above:

The process of making guest systems perform better began as soon as the customers got their hands on CP. Lynn Wheeler had done a lot of work on this while he was a student at Washington State, but he was by no means the only one who had worked on it. The CP-67 Project had frequently scheduled sessions in which customers reported on modifications to CP and guest systems to make the guests run better under CP. These customers had measured and monitored their systems to find high overhead areas and had then experimented with ways of reducing the overhead.(108) Dozens of people contributed to this effort, but I have time to mention only a few.

Dewayne Hendricks(109) reported at SHARE XLII, in March, 1974, that he had successfully implemented MVT-CP handshaking for page faulting, so that when MVT running under VM took a page fault, CP would allow MVT to dispatch another task while CP brought in the page. At the following SHARE, Dewayne did a presentation on further modifications, including support for SIOF and a memory-mapped job queue. With these changes, his system would allow multi-tasking guests actually to multi-task when running in a virtual machine. Significantly, his modifications were available on the Waterloo Tape.