L-5.21: Numerical on Translation Lookaside Buffer (TLB) | Operating System

Gate Smashers
19 Feb 202004:31

Summary

TLDRIn this tutorial, the speaker explains how to calculate the Effective Memory Access Time (EMAT) in a paging system with Translation Lookaside Buffer (TLB). They detail the process of handling TLB hits and misses, showing how to calculate the access time in each case. The video emphasizes the TLB hit ratio, which is 90%, and how to derive the EMAT formula. The final calculation yields an EMAT of 65 ns, assuming no page faults occur. This explanation simplifies the concept of memory access in systems using TLB for efficient data retrieval.

Takeaways

  • 😀 TLB (Translation Lookaside Buffer) is used to speed up memory access by caching page table entries.
  • 😀 The problem explains how to calculate the Effective Memory Access Time (EMAT) in a system with TLB.
  • 😀 TLB access time is given as 10 ns and main memory access time is 50 ns.
  • 😀 The TLB hit ratio is 90%, which means there is a 90% chance of finding the required page in the TLB.
  • 😀 If there is a miss in the TLB, the CPU needs to check the page table in main memory, which adds additional time to the access.
  • 😀 The miss ratio is the complement of the hit ratio, so in this case, the miss ratio is 10%.
  • 😀 Effective Memory Access Time (EMAT) combines both hit and miss scenarios, weighted by their respective probabilities.
  • 😀 For a hit, the total time is the sum of TLB access time (10 ns) and main memory access time (50 ns), totaling 60 ns.
  • 😀 For a miss, the total time is the sum of TLB access time (10 ns), page table lookup time (50 ns), and main memory access time (50 ns), totaling 110 ns.
  • 😀 The final EMAT is calculated as the weighted sum of hit and miss times: EMAT = 0.9(60) + 0.1(110) = 65 ns.
  • 😀 The calculation assumes no page fault, which would require additional time for page fault handling and is not considered in this scenario.

Q & A

  • What is the role of the TLB in memory access?

    -The TLB (Translation Lookaside Buffer) stores recently used page-to-frame mappings to speed up memory access. When the CPU generates a logical address, it first checks the TLB for the corresponding frame number to avoid accessing the slower main memory.

  • What happens when there is a TLB hit?

    -When there is a TLB hit, the frame number is found directly in the TLB, and the data is accessed from the corresponding page in the main memory. This results in a quicker memory access time.

  • What is the formula for calculating the Effective Memory Access Time (EMAT)?

    -The formula for EMAT is: (Hit Ratio × Hit Time) + (Miss Ratio × Miss Time). The Hit Time includes the time to access the TLB and main memory, while the Miss Time includes the time to access the TLB, the page table, and the main memory.

  • What are the access times involved in a TLB hit scenario?

    -In a TLB hit, the access time includes the TLB access time (10 ns) and the main memory access time (50 ns), resulting in a total of 60 ns for a hit.

  • How is the Miss Time different from the Hit Time?

    -The Miss Time is longer because, in addition to checking the TLB and main memory, the CPU also needs to check the page table in memory to find the correct frame. The total Miss Time is the sum of TLB access time (10 ns), page table access time (50 ns), and main memory access time (50 ns), giving 110 ns in case of a miss.

  • What is the TLB Hit Ratio in the example provided?

    -In the example, the TLB Hit Ratio is 90%, meaning there is a 90% chance that the CPU will find the required page frame in the TLB.

  • How is the TLB Miss Ratio calculated?

    -The TLB Miss Ratio is calculated as 1 minus the TLB Hit Ratio. In this case, with a 90% hit ratio, the miss ratio is 10%.

  • What is the final Effective Memory Access Time (EMAT) in this example?

    -The final EMAT is 65 ns, calculated as (0.9 × 60 ns) + (0.1 × 110 ns) = 54 ns + 11 ns = 65 ns.

  • What is the impact of a page fault on the EMAT calculation?

    -If a page fault occurs, the calculation of EMAT changes because additional time is required to bring the page from secondary storage into main memory. This would add a page fault service time to the EMAT.

  • Why is the TLB important for system performance?

    -The TLB is crucial for improving system performance by reducing memory access times. A higher TLB Hit Ratio means less time spent accessing main memory, which speeds up overall CPU performance.

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Ähnliche Tags
TLB AccessMemory AccessComputer ArchitectureEffective TimeTLB MissPaging SystemHit RatioMiss RatioMain MemoryNumerical ExampleEducational Content
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