• Journal of KIISE:Computer Systems and Theory
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• v.32 no.6
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• pp.306-313
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• 2005

Conditional branch prediction is an important technique for improving processor performance. Branch mispredictions, however, waste a large number of cycles, inhibit out-of-order execution, and waste electric power on mis-speculated instructions. Hence, the branch predictor with higher accuracy is necessary for good processor performance. In global-history-based predictors like gshare and GAg, many mispredictions come from commit update of the history. Some works on this subject have discussed the need for speculative update of the history and recovery mechanisms for branch mispredictions. In this paper, we present a simple mechanism for recovering the branch history after a misprediction. The proposed mechanism adds an age_counter to the original predictor and doubles the size of the branch history register. The age_counter counts the number of outstanding branches and uses it to recover the branch history register. Simulation results on the Simplescalar 3.0/PISA tool set and the SPECINTgS benchmarks show that gshare and GAg with the proposed recovery mechanism improved the average prediction accuracy by 2.14$\%$ and 9.21$\%$, respectively and the average IPC by 8.75$\%$ and 18.08$\%$, respectively over the original predictor.

• 월간 기계설비
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• s.259
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• pp.86-89
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• 2012

한국가스공사(사장 주강수)는 본사 및 사업소의 올해 공사 및 용역, 구매 등 1조 1,771억원의 발주계획을 발표했다. 이는 지난해 계약실적 1조2,487억원 보다 5.7% 감소한 금액이다. 분기별로는 1분기에 약 4,083억원, 2분기에 약2,573억원, 3분기에 약 2,129억원, 4분기에 약 2,987억원 등 상반기에 56.5%를 집행할 계획이다.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.41 no.6
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• pp.1-11
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• 2004

Modern processors achieve high performance exploiting avaliable Instruction Level Parallelism(ILP) by using speculative technique such as branch prediction. Traditionally, branch direction can be predicted at very high accuracy by 2-level predictor, and branch target address is predicted by Branch Target Buffer(BTB). Except for indirect branch, each of the branch has the unique target, so its prediction is very accurate via BTB. But because indirect branch has dynamically polymorphic target, indirect branch target prediction is very difficult. In general, the technique of branch direction prediction is applied to indirect branch target prediction, and much better accuracy than traditional BTB is obtained for indirect branch. We present a new indirect branch target prediction scheme which combines a indirect branch instruction with its data dependent register of the instruction executed earlier than the branch. The result of SPEC benchmark simulation which are obtained on SimpleScalar simulator shows that the proposed predictor obtains the most perfect prediction accuracy than any other existing scheme.

• Proceedings of the Korean Information Science Society Conference
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• 2003.10a
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• pp.202-204
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• 2003

EISC ISA를 기반으로 한 64 비트 고성능 내장형 마이크로프로세서 AE64000의 효과적인 성능 향상을 위해서 비용 대비 성능 향상이 우수한 분기 예측 기법을 도입하여 AE64000 파이프라인에 적합한 분기 예측기를 추가로 설계하고 SPEClnt 벤치마크 및 타 내장형 벤치마크의 성능 분석 시뮬레이션을 통해 최적의 분기 예측기의 구조를 결정하였다. AE64000에서 LERI 명령 처리를 위해 AE64000 파이프라인에 추가된 독특한 IFU에 의하여 복잡성을 갖지만, IF 단계의 PC 대신에 IFU 단계의 PrePC를 이용하여 분기 명령을 명령어 prefetch 단계에서 예측함으로써, 올바른 분기 예측시 분기로 인한 손실을 제거할 수 있다. 결과적으로 최종 선정된 최적의 분기 예측기는 Verilog로 구현하여 AE64000 프로세서 코어 모델과 통합 합성하였고 아울러 추가되는 면적과 최종 목표 클럭에 동작하기 위한 타이밍 분석을 통해 최종 생산에 적합하도록 설계된 분기 예측기의 기능 및 타이밍 검증을 수행하였다. 최종 구현된 분기 예측기는 프로세서 칩 전체의 1% 미만의 비용으로 최고 12%의 성능 향상을 달성하여 성능 대비 면적의 효율성에서 높은 결과를 보였다.

• Proceedings of the Korean Information Science Society Conference
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• 2005.11a
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• pp.766-768
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• 2005

분기 영령어의 예측 정확도는 시스템 전체 성능에 중대한 영향을 미친다. 여러 분기 예측 방식 가운데 하나인 "분기 정보의 투기적 사용" 은 분기 명령어의 가장 최근 기록을 일관되게 사용할 수 있도록 도와줌으로 해서 분기 예측의 정확도 향상에 크게 기여한다. 하지만 이와 같은 기법은 미완료 분기에 대한 히스토리를 투기적으로 사용하는 방식이다. 따라서 사용되는 정보가 올바르지 못할 수 있으며, 이런 경우 적절한 복구 기법을 필요로 한다. 본 논문에서는 분기 정보의 투기적 사용에 대한 필요성과 효율적인 복구 기법을 제안한다. 제안된 기법은 이전 연구와 비교하여 상당한 하드웨어 요구량의 감소를 가져왔으며, 또한 프로그램 수행의 정확성을 해치지 않으면서 최대 $3.3\%$의 성능향상을 보였다.

• Proceedings of the Korean Information Science Society Conference
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• 2005.07a
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• pp.808-810
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• 2005

조건 분기예측실패는 많은 사이클을 낭비시키며, 비순서적 실행을 방해하고, 잘못 예측된 명령어들을 수행하게 되므로 전력을 낭비한다. gshare와 GAg같은 전역 히스토리를 기반으로 하는 예측기에서는 히스토리의 명령어 완료시간 갱신(commit update)에 의해 많은 분기예측실패가 발생한다. 이를 위해 히스토리를 모험적으로 갱신하고, 분기예측실패 시 히스토리를 복구시키는 메커니즘에 관한 연구들이 제시되었다. 본 논문에서는 기존 분기예측기에 age_Counter를 추가하여 미해결 분기명령어 수를 저장하며, 이를 분기예측실패 후 분기 히스토리 레지스터를 복구하는데 사용하는 간단한 복구 메커니즘을 제안한다. SimpleScalar 3.0/PISA 툴셋과 SPECINT95 벤치마크 프로그램에서 시뮬레이션 한 결과, 제안된 복구 메커니즘은 GAg와 gshare 예측기에서 예측정확도는 각각 $9.21\%$와 $2.14\%$가 개선되었고, IPC는 $18.08\%$와 $8.75\%$ 개선되었다.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.44 no.2 s.314
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• pp.1-10
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• 2007

Branch prediction accuracy is critical for the overall system performance. Branch miss-prediction penalty is the one of the significant performance limiters for improving processor performance, as the pipeline deepens and the instruction issued per cycle increases. In this paper, we propose "Dynamic Per-Branch History Length Fitting Method" by tracking the data dependencies among the register writing instructions. The proposed solution first identifies the key branches, and then it selectively uses the histories of the key branches. To support this mechanism, we provide a history length adjustment algorithm and a required hardware module. As the result of simulation, the proposed mechanism outperforms the previous fixed static method, up to 5.96% in prediction accuracy. Furthermore, our method introduces the performance improvement, compared to the profiled results which are generally considered as the optimal ones.

• The KIPS Transactions:PartA
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• v.14A no.6
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• pp.347-356
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• 2007

In designing a branch predictor, in addition to accuracy, microarchitects should consider power consumption, especially for embedded processors. This paper proposes a power-aware branch predictor, which is based on the gshare predictor, by accessing the BTB (Branch Target Buffer) only when the prediction from the PHT (Pattern History Table) is taken. To enable the selective access to the BTB, the PHT in the proposed branch predictor is accessed one cycle earlier than the traditional PHT to prevent the additional delay. As a side effect, two predictions from the PHT are obtained through one access to the PHT, which leads to more power savings. The proposed branch predictor reduces the power consumption, not requiring any additional storage arrays, not incurring additional delay (except just one MUX delay) and never harming accuracy. Simulation results show that the proposed predictor reduces the power consumption by $35{\sim}48%$ compared to the traditional predictor.

• Proceedings of the Korean Association for Survey Research Conference
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• 2001.04a
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• pp.131-152
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• 2001

In this Era of Information and Localization, Gross Regional Domestic Product(GRDP) is recognized as indispensable informatin to establish regional economic policy. Especially, to raise Chungbuk provinece´s economical independence and to establish effectual regional economic development plans. Chungbuk province needs quarterly estimated GRDP for developing regional economic forecasting system. In this study, utilizing small area estimation is proposed to estimate the quarterly Chungbuk-GRDP provided by the Bureau of Statistics and nation´s GDP provid by the Bank of Korea exists. Moreover, from the nation´s quarterly GDP in each section of economical activity, this study has presumed the quarterly comovement, applied it to subdivide Chungbuk annual GRDP quarterly, and estimated quarterly Chungbuk-GRDP.

• Survey Research
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• v.2 no.2
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• pp.131-152
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• 2001

In this Era of Information and Localization. Gross Regional Domestic Product(GRDP) is recognized as indispensable information to establish regional economic policy. Especially, to raise Chungbuk province's economical independence and to establish effectual regional economic development plans, Chungbuk province needs quarterly estimated GRDP for developing regional economic forecasting system. In this study. utilizing small area estimation is proposed to estimate the quarterly Chungbuk-GRDP. To estimate quarterly GRDP. this study assumes that the comovement between the annual Chungbuk-GRDP provided by the Bureau of Statistics and nation's GDP provided by the Bank of Korea exists. Moreover, from the nation's quarterly GDP in each section of economical activity, this study has presumed the quarterly comovement. applied ft to subdivide Chungbuk annual GRDP quarterly, and estimated quarterly Chungbuk-GRDP.