Leveraging ECC to Mitigate Read Disturbance, False Reads Mitigating Bitline Crosstalk Noise in DRAM Memories and Write Faults in STT-RAM

Transcription

1 1 MEMSYS 2017 DSN 2016 Leveraging ECC to Mitigate ead Disturbance, False eads Mitigating Bitline Crosstalk Noise in DAM Memories and Write Faults in STT-AM Mohammad Seyedzadeh, akan. Maddah, Alex. Jones, ami. Melhem Mohammad Seyedzadeh*, Donald Kline Jr, Alex. Jones, ami. Melhem University of Pittsburgh University of Pittsburgh October 4, 2017

2 2 Executive Summary DAM scaling decreases proximity of cells and increases coupling noise between cells. Observation: There is a correlation between weak cells and data patterns that reduces reliability of the system. Our Approach: Periodic Flip Encoding (PFE) Fault Oblivious PFE (PFE FO ) minimizes the number of bad patterns Fault-Aware PFE (PFE FA ) minimizes (or eliminates) the occurrence of crosstalk errors using weak cell information Key results: Large improvement in eliability with a low performance overhead of between 1-2%

3 3 Motivation DAM cells

4 4 Motivation Technology Scaling DAM cells DAM cells DAM scaling enabled high capacity

5 5 Motivation Technology Scaling DAM cells DAM cells DAM scaling enabled high capacity Cell-to-cell crosstalk

6 6 Motivation The bad pattern occurs when a bit line swings in the opposite direction of its two neighboring bit lines In contrast, the best pattern happens when neighboring bit lines of a reference bit line swing in the opposite directions Bi-1 Bi Bi+1 Bi-1 Bi+1 Bi-1' Bi' Bi+1' H Bi-1' H Bi' H Bi+1' H Bi-1' Bi' H Bi+1' Bi-1 Bi Bi+1 Bi L L L L (a) Worst-case 000 (b) Worst-case 111 (c) Best-case 101

7 7 Motivation The bad pattern occurs when a bit line swings in the opposite direction of its two neighboring bit lines In contrast, the best pattern happens when neighboring bit lines of a reference bit line swing in the opposite directions Bi-1 Bi Bi+1 Bi-1 Bi+1 Bi-1' Bi' Bi+1' H Bi-1' H Bi' H Bi+1' H Bi-1' Bi' H Bi+1' Bi-1 Bi Bi+1 Bi L L L L (a) Worst-case 000 (b) Worst-case 111 (c) Best-case 101

8 Prior Solution to Bitline Crosstalk Noise Four-to-Five Encoding (FFE) DataWord Codeword DataWord Codeword

9 Prior Solution to Bitline Crosstalk Noise Four-to-Five Encoding (FFE) DataWord Codeword DataWord Codeword Dataword Codeword

10 Prior Solution to Bitline Crosstalk Noise Four-to-Five Encoding (FFE) DataWord Codeword DataWord Codeword Dataword Codeword

11 Prior Solution to Bitline Crosstalk Noise Four-to-Five Encoding (FFE) DataWord Codeword DataWord Codeword Dataword Codeword Advantage emove bad patterns from 5-bit groups Disadvantage 25% Overhead

12 Our Solution: Periodic Flip Encoding (PFE FO ) 12 Partition the data into 3-bit groups and then flip the same bit position of each group (a) (b) (c) (d) Encoding the Original Codeword

13 Our Solution: Periodic Flip Encoding (PFE FO ) 13 Partition the data into 3-bit groups and then flip the same bit position of each group (a) (b) (c) (d)

14 Our Solution: Periodic Flip Encoding (PFE FO ) 14 Partition the data into 3-bit groups and then flip the same bit position of each group (a) (b) (c) (d)

15 Our Solution: Periodic Flip Encoding (PFE FO ) 15 Partition the data into 3-bit groups and then flip the same bit position of each group (a) (b) (c) (d)

16 Our Solution: Periodic Flip Encoding (PFE FO ) 16 Partition the data into 3-bit groups and then flip the same bit position of each group (a) (b) (c) (d) Use two auxiliary bits per cache-line to specify the code word used.

17 Our Solution: Periodic Flip Encoding (PFE FO ) 17 Partition the data into 3-bit groups and then flip the same bit position of each group (a) (b) PFE FO (c) (d) Codeword with the minimum number of bad patterns

18 Our Solution: Periodic Flip Encoding (PFE FA ) 18 Fault Oblivious PFE (PFE FO ) minimizes the number of bad patterns Fault-Aware PFE (PFE FA ) minimizes (or eliminates) the occurrence of crosstalk errors using Weak Cell Map (WCM)

19 Our Solution: Periodic Flip Encoding (PFE FA ) 19 Given location of weak cells, pick the codeword with no overlap between weak cells and bad patterns (a) (b) (c) (d)

20 Our Solution: Periodic Flip Encoding (PFE FA ) 20 Given location of weak cells, pick the codeword with no overlap between weak cells and bad patterns (a) (b) (c) (d)

21 Our Solution: Periodic Flip Encoding (PFE FA ) 21 1 Modified Memory Controller PFE FA Last Level Cache Address bit Data / WCM Encoder Module_0 Encoder Module_1 Encoder Module_14 Encoder Module_15 5 CW Original Memory Controller CW0 Encoder Module_ i Encoder_0 Memory controller implementation of fault aware PFE FA CW1 CW2 CW3 Encoder_1 Encoder_2 Encoder_3 4:1 Mux CW_ ij Main Memory WCM 4 2:4 Encoder 2

22 Experimental Methodology 22 We use PIN-based simulator to model the cache hierarchy in order to determine the accesses to main memory. CPU L1 Cache L2 Cache Cache Block Write Buffer 4-core, 8-issue width per core, out of order 16K private Inst. & Data, 8-way set-assoc. 1MB shared 16-way set-assoc. 512-bits 64-entries Benchmark Weak Cell Map PASEC, SPEC CPU2006 Bayesian distribution Fault ate 0.01%, 0.1%, 1%

23 Experimental Methodology 23 Uncorrectable Bit Error ate (UBE) ECPFO: protect against potential faults by pointing to weak cells and providing reliable storage for their content. ECPFA: pointing to and storing the values of weak cells that overlap with the center of any bad pattern. ECC-k FFE PFE ECP-k Overhead per n-bit block K[log(n)]+1 [n/4] 2 k([log(n)]+1)+1 ECC-1 32 ECC-2 32 ECC FFE PFE ECP-3 ECP-12 Block size Overhead bits per block Overhead % 18.75% 34.37% 6.25% 25% 6.25% 6.05% 23.63%

24 Experimental Methodology 24 Uncorrectable Bit Error ate (UBE) ECPFO: protect against potential faults by pointing to weak cells and providing reliable storage for their content ECPFA: pointing to and storing the values of weak cells that overlap with the center of any bad pattern ECC-k FFE PFE ECP-k Overhead per n-bit block K[log(n)]+1 [n/4] 2 k([log(n)]+1)+1 ECC-1 32 ECC-2 32 ECC FFE PFE ECP-3 ECP-12 Block size Overhead bits per block Overhead % 18.75% 34.37% 6.25% 25% 6.25% 6.05% 23.63% ISO-area

25 Experimental Methodology 25 Uncorrectable Bit Error ate (UBE) ECPFO: protect against potential faults by pointing to weak cells and providing reliable storage for their content ECPFA: pointing to and storing the values of weak cells that overlap with the center of any bad pattern ECC-k FFE PFE ECP-k Overhead per n-bit block K[log(n)]+1 [n/4] 2 k([log(n)]+1)+1 ECC-1 32 ECC-2 32 ECC FFE PFE ECP-3 ECP-12 Block size Overhead bits per block Overhead % 18.75% 34.37% 6.25% 25% 6.25% 6.05% 23.63% ISO-area

26 UBE (Lower is BeUer) 1.E-04 1.E-05 1.E-06 1.E-07 1.E-08 1.E-09 UBE (0.01% incidence of weak cells) FFE ECP -12 PFE +ECC-1 FO FO 32 blackscholes bodytrack ferret fluidanimate freqmine raytrace swapcons vips x264 canneal dedup streamcluster parsec mean bzip2 gobmk hmmer 26 libquantum mcf sjeng cactusadm calculix GemsFDTD lbm milc namd spec mean mean

27 UBE (0.01% incidence of weak cells) 27 1.E-04 FFE ECP -12 PFE +ECC-1 FO FO 32 UBE (Lower is BeUer) UBE (Lower is BeUer) 1.E-05 1.E-06 1.E-07 1.E-08 1.E-09 1.E-04 1.E-05 1.E-06 1.E-07 1.E-08 1.E-09 1.E-10 1.E-11 1.E-12 blackscholes bodytrack ferret fluidanimate freqmine raytrace swapcons vips x264 ECC-1 ECP -3 PFE 128 blackscholes bodytrack ferret fluidanimate freqmine raytrace swapdons vips x264 canneal dedup streamcluster parsec mean canneal dedup streamcluster parsec mean bzip2 gobmk hmmer libquantum FA FA mcf sjeng cactusadm calculix GemsFDTD lbm milc namd spec mean mean bzip2 gobmk hmmer libquantum mcf sjeng cactusadm calculix GemsFDTD lbm milc namd spec mean mean 10-6

28 Performance (IPC) overhead of being cost aware 28 Baseline(PFE FO ): Fault-oblivious scheme MemCTL(PFE FA ): Encoding in MemCTL with Fault information cached in MemCTL MemDIMM(PFE FA ): Encoding in DIMM with Fault information resides on DIMM Baseline MemCTL MemDIMM IPC blackscholes bodytrack ferret fluidanimate freqmine raytrace swap>ons vips x264 canneal dedup streamcluster parsec mean bzip2 gobmk hmmer libquantum mcf sjeng cactusadm calculix GemsFDTD lbm milc namd spec mean mean

29 UBE for different fault mitigation schemes 29 UBE (Lower is Be:er) 1.E-02 1.E-03 1.E-04 1.E-05 1.E-06 1.E-07 1.E-08 <1.0E-11 1.E % 0.10% 1.00% Less than

30 30 Conclusion DAM scaling decreases proximity of cells and increases coupling noise between cells. Observation: There is a correlation between weak cells and data patterns that reduces reliability of the system. Our Approach: Periodic Flip Encoding (PFE) Fault Oblivious PFE (PFE FO ) minimizes the number of bad patterns Fault-Aware PFE (PFE FA ) minimizes (or eliminates) the occurrence of crosstalk errors using weak cell information Key results: Large improvement in eliability with a low performance overhead of between 1-2%

31 31 MEMSYS 2017 DSN 2016 Leveraging ECC to Mitigate ead Disturbance, False eads Mitigating Bitline Crosstalk Noise in DAM Memories and Write Faults in STT-AM Mohammad Seyedzadeh, akan. Maddah, Alex. Jones, ami. Melhem Mohammad Seyedzadeh*, Donald Kline Jr, Alex. Jones, ami. Melhem University of Pittsburgh University of Pittsburgh October 4, 2017