Commonly Used Metrics for Performance Analysis - Power.org

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Metrics for Performance Analysis9 Branch PredictionThis chapter lists and describes the events, metrics and groups needed to characterize branch mispredictionand branches taken.9.1Descriptions of EventsThere are 12 events, distributed across 4 event groups, needed for these POWER7 branch predictionmetrics. These include 1 architected event counting non-idle completed instructions.This section provides more details on each event and how it is triggered.PM_BR_MPREDNumber of Branch MispredictsA branch instruction was predicted. This could have been a target prediction a condition prediction or bothPM_BR_MPRED_CCACHEBranch Mispredict due to Count Cache predictionA branch instruction target was incorrectly predicted due to count cache misprediction. This will result in abranch mispredict flush unless a flush is detected from an older instruction.PM_BR_MPRED_CRBranch mispredict - taken/not takenA conditional branch instruction was incorrectly predicted as taken or not taken. The branch execution unitdetects a branch mispredict because the CR value is opposite of the predicted value. This will result in abranch redirect flush if not overfidden by a flush of an older instruction.PM_BR_MPRED_LSTACKBranch Mispredict due to Link StackA branch instruction target was incorrectly predicted due to Link stack Misprediction. This will result in abranch mispredict flush unless a flush is detected from an older instruction.PM_BR_MPRED_TABranch mispredict - target addressA branch instruction target was incorrectly predicted. This will result in a branch mispredict flush unless aflush is detected from an older instruction.PM_BR_PREDBranch Predictions madeA branch prediction was made, counted at branch execute time.PM_BR_PRED_CCACHECount Cache PredictionsA branch instruction target prediction was made using the count cachePM_BR_PRED_CRBranch predict - taken/not takenA conditional branch instruction was predicted as taken or not taken.PM_BR_PRED_LSTACKLink Stack PredictionsA branch instruction target prediction was made using the Link stackPM_BR_TAKENBranch TakenA branch instruction was taken. This could have been a conditional branch or an unconditional branchPM_BRU_FINBranch Instruction FinishedThe branch unit finished a branch type instruction.PM_RUN_INST_CMPLRun InstructionsNumber of PowerPC instructions completed, gated by the run latch.9.2 MetricsBranch prediction is characterized with the following metrics:Copyright ©2011 IBM Corporation Page 28 of 52
Metrics for Performance AnalysisBranch_Mispredict_Rate(%)Branch mispredictions per instructionFormula: PM_BR_MPRED / PM_RUN_INST_CMPL * 100CR_Mispredict_Rate(%)CR mispredictions per InstructionFormula: PM_BR_MPRED_CR / PM_RUN_INST_CMPL * 100TA_Mispredict_Rate(%)branch target address mispredictions per InstructionFormula: PM_BR_MPRED_TA / PM_RUN_INST_CMPL * 100LSTACK_Mispredict_Rate(%) Link stack branch mispredictionFormula: (PM_BR_MPRED_TA - PM_BR_MPRED_CCACHE) / PM_RUN_INST_CMPL * 100CCACHE_Mispredict_Rate(%) Count cache branch misprediction per instructionFormula: PM_BR_MPRED_CCACHE / PM_RUN_INST_CMPL * 100Taken_Branches(%)% Branches TakenFormula: PM_BR_TAKEN * 100 / PM_BRU_FINBR_Misprediction(%)Branch mispredictions per branch predictionFormula: PM_BR_MPRED / PM_BR_PRED * 100TA_Misprediction(%)branch target address mispredictions per branch target addresspredictionFormula: PM_BR_MPRED_TA / (PM_BR_PRED_CCACHE + PM_BR_PRED_LSTACK) * 100CR_Misprediction(%)branch CR mispredictions per branch CR predictionFormula: PM_BR_MPRED_CR / PM_BR_PRED_CR * 100CCACHE_Misprediction(%)Count cache branch mispredictionFormula: PM_BR_MPRED_CCACHE / PM_BR_PRED_CCACHE * 100LSTACK_Misprediction(%)Link stack branch mispredictionFormula: (PM_BR_MPRED_TA - PM_BR_MPRED_CCACHE) / PM_BR_PRED_LSTACK * 100Copyright ©2011 IBM Corporation Page 29 of 52
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Commonly Used Metrics for Performance Analysis - Power.org

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