buzzword
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buzzword [2014/03/03 18:16] rachata |
buzzword [2014/03/26 18:17] rachata |
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| * Intel IA-64 | * Intel IA-64 | ||
| * Static instruction scheduling and VLIW | * Static instruction scheduling and VLIW | ||
| + | |||
| + | ===== Lecture 19 (3/19 Wed.) ===== | ||
| + | |||
| + | * Ideal cache | ||
| + | * More capacity | ||
| + | * Fast | ||
| + | * Cheap | ||
| + | * High bandwidth | ||
| + | * DRAM cell | ||
| + | * Cheap | ||
| + | * Sense the purturbation through sense amplifier | ||
| + | * Slow and leaky | ||
| + | * SRAM cell (Cross coupled inverter) | ||
| + | * Expensice | ||
| + | * Fast (easier to sense the value in the cell) | ||
| + | * Memory bank | ||
| + | * Read access sequence | ||
| + | * DRAM: Activate -> Read -> Precharge (if needed) | ||
| + | * What dominate the access laatency for DRAM and SRAM | ||
| + | * Scaling issue | ||
| + | * Hard to scale the scale to be small | ||
| + | * Memory hierarchy | ||
| + | * Prefetching | ||
| + | * Caching | ||
| + | * Spatial and temporal locality | ||
| + | * Cache can exploit these | ||
| + | * Recently used data is likely to be accessed | ||
| + | * Nearby data is likely to be accessed | ||
| + | * Caching in a pipeline design | ||
| + | * Cache management | ||
| + | * Manual | ||
| + | * Data movement is managed manually | ||
| + | * Embedded processor | ||
| + | * GPU scratchpad | ||
| + | * Automatic | ||
| + | * HW manage data movements | ||
| + | * Latency analysis | ||
| + | * Based on the hit and miss status, next level access time (if miss), and the current level access time | ||
| + | * Cache basics | ||
| + | * Set/block (line)/Placement/replacement/direct mapped vs. associative cache/etc. | ||
| + | * Cache access | ||
| + | * How to access tag and data (in parallel vs serially) | ||
| + | * How do tag and index get used? | ||
| + | * Modern processors perform serial access for higher level cache (L3 for example) to save power | ||
| + | * Cost and benefit of having more associativity | ||
| + | * Given the associativity, which block should be replace if it is full | ||
| + | * Replacement poligy | ||
| + | * Random | ||
| + | * Least recently used (LRU) | ||
| + | * Least frequently used | ||
| + | * Least costly to refetch | ||
| + | * etc. | ||
| + | * How to implement LRU | ||
| + | * How to keep track of access ordering | ||
| + | * Complexity increases rapidly | ||
| + | * Approximate LRU | ||
| + | * Victim and next Victim policy | ||
| + | |||
| + | ===== Lecture 20 (3/21 Fri.) ===== | ||
| + | |||
| + | * Set thrashing | ||
| + | * Working set is bigger than the associativity | ||
| + | * Belady's OPT | ||
| + | * Is this optimal? | ||
| + | * Complexity? | ||
| + | * Similarity between cache and page table | ||
| + | * Number of blocks vs pages | ||
| + | * Time to find the block/page to replace | ||
| + | * Handling writes | ||
| + | * Write through | ||
| + | * Need a modified bit to make sure accesses to data got the updated data | ||
| + | * Write back | ||
| + | * Simpler, no consistency issues | ||
| + | * Sectored cache | ||
| + | * Use subblock | ||
| + | * lower bandwidth | ||
| + | * more complex | ||
| + | * Instruction vs data cache | ||
| + | * Where to place instructions | ||
| + | * Unified vs. separated | ||
| + | * In the first level cache | ||
| + | * Cache access | ||
| + | * First level access | ||
| + | * Second level access | ||
| + | * When to start the second level access | ||
| + | * Performance vs. energy | ||
| + | * Address translation | ||
| + | * Homonym and Synonyms | ||
| + | * Homonym: Same VA but maps to different PA | ||
| + | * With multiple processes | ||
| + | * Synonyms: Multiple VAs map to the same PA | ||
| + | * Shared libraries, shared data, copy-on-write | ||
| + | * I/O | ||
| + | * Can these create problems when we have the cache | ||
| + | * How to eliminate these problems? | ||
| + | * Page coloring | ||
| + | * Interaction between cache and TLB | ||
| + | * Virtually indexed vs. physically indexed | ||
| + | * Virtually tagged vs. physically tagged | ||
| + | * Virtually indexed physically tagged | ||
| + | * Virtual memory in DRAM | ||
| + | * Control where data is mapped to in channel/rank/bank | ||
| + | * More parallelism | ||
| + | * Reduce interference | ||
| + | |||
| + | ===== Lecture 21 (3/24 Mon.) ===== | ||
| + | |||
| + | |||
| + | |||
| + | * Different parameters that affect cache miss | ||
| + | * Thrashing | ||
| + | * Different types of cache misses | ||
| + | * Compulsory misses | ||
| + | * Can mitigate with prefetches | ||
| + | * Capacity misses | ||
| + | * More assoc | ||
| + | * Victim cache | ||
| + | * Conflict misses | ||
| + | * Hashing | ||
| + | * Large block vs. small block | ||
| + | * Subblocks | ||
| + | * Victim cache | ||
| + | * Small, but fully assoc. cache behind the actual cache | ||
| + | * Cached misses cache block | ||
| + | * Prevent ping-ponging | ||
| + | * Pseudo associativity | ||
| + | * Simpler way to implement associative cache | ||
| + | * Skewed assoc. cache | ||
| + | * Different hashing functions for each way | ||
| + | * Restructure data access pattern | ||
| + | * Order of loop traversal | ||
| + | * Blocking | ||
| + | * Memory level parallelism | ||
| + | * Cost per miss of a parallel cache miss is less costly compared to serial misses | ||
| + | * MSHR | ||
| + | * Keep track of pending cache | ||
| + | * Think of this as the load/store buffer-ish for cache | ||
| + | * What information goes into the MSHR? | ||
| + | * When do you access the MSHR? | ||
| + | |||
| + | |||
| + | ===== Lecture 22 (3/26 Wed.) ===== | ||
| + | |||
| + | |||
| + | |||
| + | * Multi-porting | ||
| + | * Virtual multi-porting | ||
| + | * Time-share the port, not too scalable but cheap | ||
| + | * True multiporting | ||
| + | * Multiple cache copies | ||
| + | * Banking | ||
| + | * Can have bank conflict | ||
| + | * Extra interconnects across banks | ||
| + | * Address mapping can mitigate bank conflict | ||
| + | * Common in main memory (note that regFile in GPU is also banked, but mainly for the pupose of reducing complexity) | ||
| + | * Accessing DRAM | ||
| + | * Row bits | ||
| + | * Column bits | ||
| + | * Addressibility | ||
| + | * DRAM has its own clock | ||
| + | * DRAM (2T) vs. SRAM (6T) | ||
| + | * Cost | ||
| + | * Latency | ||
| + | * Interleaving in DRAM | ||
| + | * Effects from address mapping on memory interleaving | ||
| + | * Effects from memory access patterns from the program on interleaving | ||
| + | * DRAM Bank | ||
| + | * To minimize the cost of interleaving (Shared the data bus and the command bus) | ||
| + | * DRAM Rank | ||
| + | * Minimize the cost of the chip (a bundle of chips operated together) | ||
| + | * DRAM Channel | ||
| + | * An interface to DRAM, each with its own ranks/banks | ||
| + | * DIMM | ||
| + | * More DIMM adds the interconnect complexity | ||
| + | * List of commands to read/write data into DRAM | ||
| + | * Activate -> read/write -> precharge | ||
| + | * Activate moves data into the row buffer | ||
| + | * Precharge prepare the bank for the next access | ||
| + | * Row buffer hit | ||
| + | * Row buffer conflict | ||
| + | * Scheduling memory requests to lower row conflicts | ||
| + | * Burst mode of DRAM | ||
| + | * Prefetch 32-bits from an 8-bit interface if DRAM needs to read 32 bits | ||
| + | * Address mapping | ||
| + | * Row interleaved | ||
| + | * Cache block interleaved | ||
| + | * Memory controller | ||
| + | * Sending DRAM commands | ||
| + | * Periodically send commands to refresh DRAM cells | ||
| + | * Ensure correctness and data integrity | ||
| + | * Where to place the memory controller | ||
| + | * On CPU chip vs. at the main memory | ||
| + | * Higher BW on-chip | ||
| + | * Determine the order of requests that will be serviced in DRAM | ||
| + | * Request queues that hold requests | ||
| + | * Send requests whenever the request can be sent to the bank | ||
| + | * Determine which command (across banks) should be sent to DRAM | ||
| + | * Priority of demand vs. prefetch requests | ||
| + | * Memory scheduling policies | ||
| + | * FCFS | ||
| + | * FR-FCFS | ||
| + | * Capped FR-FCFS: FR-FCFS with a timeout | ||
| + | * Usually this is done in a command level (read/write commands and precharge/activate commands) | ||
| + | | ||
| + | | ||
| + | | ||
buzzword.txt · Last modified: 2015/04/27 18:20 by rachata
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