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include vmm.inc
 
mov     eax, PriorityBoost    ; signed integer specifying priority boost
mov     ebx, VM               ; VM handle
VMMcall Adjust_Exec_Priority
 
The Adjust_Exec_Priority service raises or lowers the execution priority of
the specified virtual machine. The service adds the specified boost to the
virtual machine's current execution priority.
 
Parameter      Description
────────────────────────────────────────────────────────────────────────────
 
PriorityBoost  Specifies a positive or negative priority boost for the
               virtual machine. This parameter must be a value such that
               when added to the current execution priority, the result is
               within the range Reserved_Low_Boost to Reserved_High_Boost.
 
               The following lists some common priority boost values:
 
               Value                   Meaning
               ─────────────────────────────────────────────────────────────
               Reserved_Low_Boost      Reserved for use by system.
 
               Cur_Run_VM_Boost        The time-slice scheduler uses this
                                       value to force a virtual machine to
                                       run for its allotted time-slice.
 
               Low_Pri_Device_Boost    Virtual devices use this value for
                                       events that need timely processing
                                       but are not time critical.
 
               High_Pri_Device_Boost   Virtual devices use this value for
                                       events that need timely processing
                                       but should not circumvent operations
                                       that have a critical section boost.
 
               Critical_Section_Boost  The system uses this value for
                                       virtual machines specified in a call
                                       to the Begin_Critical_Section
                                       service.
 
               Time_Critical_Boost     Virtual devices use this value for
                                       events that must be processed even
                                       when another virtual machine is in a
                                       critical section. For example, VPICD
                                       uses this when simulating hardware
                                       interrupts.
 
               Reserved_High_Boost     Reserved for use by system.
 
VM             Specifies the handle identifying the virtual machine.
 
Return Value
 
This service has no return value.
 
Comments
 
Since the nonsuspended virtual machine with the highest execution priority
is always the current virtual machine, this service causes a task switch
under two circumstances:
 
1  The execution priority of the current virtual machine is lowered (EAX is
   negative), and there is another virtual machine with a higher priority
   that is not suspended.
 
2  The execution of a nonsuspended virtual machine which is not the current
   virtual machine is raised (EAX is positive) higher than the current
   virtual machine's execution priority.
 
Even if the current virtual machine is in a critical section, a task switch
will still occur if the priority of another nonsuspended virtual machine is
raised higher than the current virtual machine's priority. However, this
will only occur when a virtual machine is given a time-critical boost, for
example, to simulate a hardware interrupt.
 
It is often more convenient to call the Call_Priority_VM_Event service than
to call this service directly.
 
Uses
 
Flags
 
See Also
 
Begin_Critical_Section, Call_Priority_VM_Event
 
 
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