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If a system uses a multi-level page table and a TLB, how does this affect the calculation of Effective Access Time (EAT) compared to a single-level page table system?

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Operating Systems - TLB - Translation Lookaside Buffer & Effective Access Time
If a system uses a multi-level page table and a TLB, how does this affect the calculation of Effective Access Time (EAT) compared to a single-level page table system?
AEAT remains the same because TLB hides all page table lookup costs
BEAT decreases because multi-level page tables reduce page faults
CEAT increases because page table lookup time is longer, so TLB misses are more expensive
DEAT is unaffected by page table structure, only by TLB hit ratio
Step-by-Step Solution

  1. Step 1: Understand multi-level page tables

    Multi-level page tables require multiple memory accesses per lookup, increasing page table access time.

  2. Step 2: Impact on EAT

    On TLB miss, page table lookup is longer, so miss penalty increases, raising EAT.

  3. Step 3: Analyze options

    A: Incorrect, TLB does not hide all page table lookup costs.
    B: Incorrect, multi-level page tables do not reduce page faults.
    C: Correct, longer page table lookup time increases EAT on misses.
    D: Incorrect, page table structure affects miss penalty and thus EAT.

  4. Final Answer:

    Option C -> Option C

  5. Quick Check:

    Longer page table lookup -> higher miss penalty -> higher EAT.
Quick Trick: Multi-level page tables -> longer lookup -> higher EAT on TLB miss [OK]
Common Mistakes:
MISTAKES
  • Assuming TLB hides all page table lookup costs
  • Confusing page fault rate with page table lookup time
Trap Explanation:
PITFALL
  • Option A is tempting because TLB speeds up translation, but misses are costlier with multi-level tables.
Interviewer Note:
CONTEXT
  • Tests deep understanding of how page table structure affects EAT in presence of TLB.
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