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8-70 Vol. 3
MULTIPLE-PROCESSOR MANAGEMENT
// C1 handler uses a Halt instruction
VOID C1Handler()
{STI
HLT
}
The MONITOR and MWAIT instructions may be considered for use in the C0 idle state loops, if
MONITOR and MWAIT are supported.
Example 8-25. An OS Idle Loop with MONITOR/MWAIT in the C0 Idle Loop
// WorkQueue is a memory location indicating there is a thread
// ready to run. A non-zero value for WorkQueue is assumed to
// indicate the presence of work to be scheduled on the processor.
// The following example assumes that the necessary padding has been
// added surrounding WorkQueue to eliminate false wakeups
// The idle loop is entered with interrupts disabled.
WHILE (1) {
IF (WorkQueue) THEN {
// Schedule work at WorkQueue.
} ELSE {
// No work to do - wait in appropriate C-state handler depending
// on Idle time accumulated.
IF (IdleTime >= IdleTimeThreshhold) THEN {
// Call appropriate C1, C2, C3 state handler, C1
// handler shown below
MONITOR WorkQueue // Setup of eax with WorkQueue
// LinearAddress,
// ECX, EDX = 0
IF (WorkQueue != 0) THEN {
MWAIT
}
}
}
}
// C1 handler uses a Halt instruction.
VOID C1Handler()
{STI
HLT