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Cache Management

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Hardware Cache Management & Linux (Buffer / Page) Cache Management

Publicado en: Tecnología
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Cache Management

  1. 1. © 2019 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. Cache Management
  2. 2. 2© 2019 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. What to Expect? Cache Fundamentals How's of Cache Cache Organization Cache Pitfalls
  3. 3. 3© 2019 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. Cache Fundamentals Mismatch between the RAM & CPU speed Transfer rate Latency to access the RAM Static Vs Dynamic RAM Systems have Dynamic RAM, which is slower Static RAM is fast but expensive Small static RAM between CPU & Dynamic RAM This is known as Cache
  4. 4. 4© 2019 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. How's of Cache Located inside the CPU Copies most recently accessed data from the RAM memory to the static memory The goal is to make CPU access the memory cache instead of accessing directly the RAM memory We call it a ‘cache miss’ if the data is not present in the cache The circuit called cache controller loads the data into cache
  5. 5. 5© 2019 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. How's of Cache ... The CPU asks for the memory / data stored in address ‘A’ Since contents are not in cache, would be fetched from RAM The cache controller loads the line (typically 64 bytes) starting at address ‘A’ The circuit called prefetcher loads more data located after this line Branch prediction since program is not always sequential
  6. 6. 6© 2019 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. Cache Organization Direct Mapping Divide the memory as per the number of cache lines Simplest configuration, requires less meta data Higher chances of cache misses Fully Associative Any memory could be loaded into any cache line Most efficient cache organization Extremely complex control logic
  7. 7. 7© 2019 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. Cache Organization ... Hybrid solution called set associative Memory cache is divided in several blocks (sets) containing ‘n’ lines each With this, the memory from the single block can be put into one of the ‘n’ cache lines in the set
  8. 8. 8© 2019 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. Direct Mapping Line 1 Line 2 ... Line 8192 128KB 128KB 128
  9. 9. 9© 2019 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. Set Associative Cache Line 1– Line 4 Line 5 – Line 8 ... Line 2048 128KB 128KB 128
  10. 10. 10© 2019 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. Cache Pitfalls Stale data May severely degrade the system performance if the program is not cache local
  11. 11. 11© 2019 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. Linux Page Cache Basics Accelerates many accesses to files on non volatile storage During reads / writes to disk, Linux stores data in unused areas of memory, which acts as cache free -m
  12. 12. 12© 2019 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. What all have we learnt? Cache Fundamentals How's of Cache Cache Organization Cache Pitfalls
  13. 13. 13© 2019 SysPlay Workshops <workshop@sysplay.in> All Rights Reserved. Any Queries?

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