lec_11_pipelining_4_spr08_s - EE-449 Lec 11Lecture 11 –...

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Unformatted text preview: EE-449 Lec. 11Lecture 11 – PipeliningEE-449 Computer Organization Spring 2008Salvador FallorinaCSULAReview: Data and Control Hazards05-07-081Fallorina | CSULAEE-449 Lec. 11Review: Data Dependenciessub $2, $1, $3and $12, $2, $5or $13, $6, $2add $14, $2, $2sw $15, 100($2)Fallorina | CSULA2• First instruction, sub, stores the result into register $2• Register $2 is used as a source by the rest of the instructions EE-449 Lec. 11Review: Detecting DependenciesFallorina | CSULA3• Dependency arrows indicate flow of data between instructions • Register $2 is updated by the first instruction, sub, in cycle 5.• But is needed by: • second instruction, and, in cycle 3• third instruction, or, in cycle 4• fourth instruction, add, in cycle 5• fifth instruction, sw, in cycle 6EE-449 Lec. 11Review: Data HazardsFallorina | CSULA4• Any arrow that points backward in time are data hazards• There is a data hazard between instruction 1 (sub) and 2 (and)• There is a data hazard between instruction 1 (sub) and 3 (or)• Fourth instruction, add, is OK• Fifth instruction, sw, is OKEE-449 Lec. 11Review: Data Hazard Solution 1- Software•Have compiler get rid of data hazards:–Rescheduling instructions–Stall for two cycles with nopsFallorina | CSULA5Problem: can’t rely on compiler and stalls slow us down!EE-449 Lec. 11Review: Data Hazard Solution 2- Forwarding•Forwarding data (by bypassing the register file)Fallorina | CSULA6EE-449 Lec. 11Review: Datapath with Forwarding UnitFallorina | CSULA7EE-449 Lec. 11Data Hazards from loadslw $1, 0($2)add $3, $1, $2Fallorina | CSULA8EE-449...
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lec_11_pipelining_4_spr08_s - EE-449 Lec 11Lecture 11 –...

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