YIELD is a hint instruction. Software with a multithreading capability can use a YIELD instruction to indicate to the PE that it is performing a task, for example a spin-lock, that could be swapped out to improve overall system performance. The PE can use this hint to suspend and resume multiple software threads if it supports the capability.
For more information about the recommended use of this instruction, see The YIELD instruction.
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SystemHintOp op; case CRm:op2 of when '0000 000' op = SystemHintOp_NOP; when '0000 001' op = SystemHintOp_YIELD; when '0000 010' op = SystemHintOp_WFE; when '0000 011' op = SystemHintOp_WFI; when '0000 100' op = SystemHintOp_SEV; when '0000 101' op = SystemHintOp_SEVL; when '0010 000' if !HaveRASExt() then EndOfInstruction(); // Instruction executes as NOP op = SystemHintOp_ESB; when '0010 001' if !HaveStatisticalProfiling() then EndOfInstruction(); // Instruction executes as NOP op = SystemHintOp_PSB; when '0010 100' op = SystemHintOp_CSDB; otherwise EndOfInstruction(); // Instruction executes as NOP
case op of when SystemHintOp_YIELD Hint_Yield(); when SystemHintOp_WFE if IsEventRegisterSet() then ClearEventRegister(); else if PSTATE.EL == EL0 then // Check for traps described by the OS which may be EL1 or EL2. AArch64.CheckForWFxTrap(EL1, TRUE); if PSTATE.EL IN {EL0, EL1} && EL2Enabled() && !IsInHost() then // Check for traps described by the Hypervisor. AArch64.CheckForWFxTrap(EL2, TRUE); if HaveEL(EL3) && PSTATE.EL != EL3 then // Check for traps described by the Secure Monitor. AArch64.CheckForWFxTrap(EL3, TRUE); WaitForEvent(); when SystemHintOp_WFI if !InterruptPending() then if PSTATE.EL == EL0 then // Check for traps described by the OS which may be EL1 or EL2. AArch64.CheckForWFxTrap(EL1, FALSE); if PSTATE.EL IN {EL0, EL1} && EL2Enabled() && !IsInHost() then // Check for traps described by the Hypervisor. AArch64.CheckForWFxTrap(EL2, FALSE); if HaveEL(EL3) && PSTATE.EL != EL3 then // Check for traps described by the Secure Monitor. AArch64.CheckForWFxTrap(EL3, FALSE); WaitForInterrupt(); when SystemHintOp_SEV SendEvent(); when SystemHintOp_SEVL SendEventLocal(); when SystemHintOp_ESB SynchronizeErrors(); AArch64.ESBOperation(); if PSTATE.EL IN {EL0, EL1} && EL2Enabled() then AArch64.vESBOperation(); TakeUnmaskedSErrorInterrupts(); when SystemHintOp_PSB ProfilingSynchronizationBarrier(); when SystemHintOp_CSDB ConsumptionOfSpeculativeDataBarrier(); otherwise // do nothing
Internal version only: isa v32.13, AdvSIMD v29.04, pseudocode morello-2022-01_rc2, capabilities morello-2022-01_rc2 ; Build timestamp: 2022-01-11T11:23
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