作者bernachom (Terry)
看板Grad-ProbAsk
标题[问题] page fault
时间Thu May 14 23:29:03 2009
想确认一下..是不是我搞错了..
题目是:
A computer whose processes have 1024 pages in their address
spaces keeps its page tables in memory. The overhead required for
reading a word from the page table is 500 nsec. In order to reduce
the overhead, the computer has a TLB,which holds 32(virtual page,
physical page frame) pairs, and can do a look up in 100 nsec.
What hit rate is needed to reduce the mean overhead to 200 nesec?
书上写: 假设TLB的hit rate 为h，则:
100ns+(1-h)*500ns=200ns
h=80%
我的问题是，那为什麽100ns不需要乘上h呢?
谢谢帮忙
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1F：推 f31816:因为那是去TLB找所花之时间 去找了才知有没有在TLB中 05/15 02:20
2F：→ f31816:没找到会要再多花500ns去page table找 05/15 02:20
3F：→ f31816:我们无法事先预知在TLB中会找到否 所以找到机率与其无关 05/15 02:21
4F：→ f31816:必定要在TLB找一次 05/15 02:22
5F：→ bernachom:点醒我了，大概是我太久没念了...谢谢您 05/15 02:33