Selecting processor micro-threading mode

1. A method that dynamically selects a micro-threading (MT) mode of each core of a processor based on a load on each of the respective cores while the processor is running a hypervisor, the method comprising:

dynamically setting a selected core's micro-threading mode to a whole-core mode (MT 1 ) in response to identifying that the load on the selected core is at a first load level;

dynamically setting the selected core's micro-threading mode to a two-way micro-threading mode (MT 2 ) in response to identifying that the load on the selected core has increased above the first load level to a second load level;

dynamically setting the selected core's micro-threading mode to a four-way micro-threading mode (MT 4 ) in response to identifying that the load on the selected core has increased above the second load level to a third load level;

entering a quest context after the setting of the micro-threading mode; and

switching the micro-threading mode of the selected core to the whole-core mode (MT 1 ) upon the selected core exiting from the guest context.

2. The method of claim 1 further comprising:

selecting a primary virtual core to execute on the selected core;

scanning a plurality of preempted virtual cores; and

selecting one or more of the preempted virtual cores to execute as secondary virtual cores along with the primary virtual core.

3. The method of claim 2 further comprising:

selecting the micro-threading mode based on the selection of the secondary virtual cores.

4. The method of claim 3 further comprising:

in response to a task executing on the primary virtual core requiring a service from a host process:

placing the task on a preempted virtual cores list corresponding to a current CPU; and

selecting a different task to execute on the primary virtual core.

5. The method of claim 4 further comprising:

performing the service by the host process on the task; and

removing the task from the preempted virtual cores list.

6. The method of claim 3 further comprising:

performing any needed service in a host process in response to exiting from the guest context; and

for each virtual CPU (vCPU) task scheduled to execute on the selected virtual core:

add an entry to a vCore data structure pertaining to each vCPU task that is ready to execute on the selected virtual core;

selecting one of the vCPU tasks as the runner task for the selected virtual core, wherein the runner task executes on the primary virtual core; and

selecting one or more of the vCPU tasks as tasks to execute concurrently with the runner task on the selected virtual core.