Basic page table question

Question

Consider a system implementing a 2 level page table. Memory access time = 10ns. Hit ratio of page table = 0.3.  Page fault access time = 50ns.

What is average access time ?

Here my doubt is when considering page hit, do we write it as 0.3(10) or 0.3(10+10+10) as we need to access 2 page tables first and then access main memory for hit ?

Comments

I just tagged @Arjun sir so that all of us could get a proper answer which was needed as these type of questions often appear in gate paper and we directly use these formulas. I don't think there is anything wrong in tagging or asking a senior person for help in-between. Anyway, thanks for your help.

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@Rupendra is correct. It is often difficult to explain one concept including all others. So, while explaining page faults -- the page table access time is often neglected in books -- we can assume 100% TLB hit. In GATE question we should consider all details given and then start solving as per that. Those who predetermine formula wont get correct answer and that is what IIT professors also want.

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@Arjun, Thanks a lot for confirming. Can you help me with another question here regarding the formula ? https://gateoverflow.in/152838/basic-doubt-in-hierarchical-cache-formula