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Jul 18, 2019
Let p be the probability of a page fault (0 s p 5 1). We would expect p to
be close to zero—that is, we would expect to have only a few page faults. The
effective access time is then
effective access time = (1 - p) x ma + p x page fault time.
To compute the effective access time, we must know how much time is
needed to service a page fault. A page fault causes the following sequence to
1. Trap to the operating system.
2. Save the user registers and process state.
3. Determine that the interrupt was a page fault. '
4. Check that the page reference was legal and determine the location of the
page on the disk.
5. Issue a read from the disk to a free frame:
a. Wait in a queue for this device until the read request is serviced.
b. Wait for the device seek and /or latency time.
c. Begin the transfer of the page to a free frame.
6. While waiting, allocate the CPU to some other user (CPU scheduling,
7. Receive an interrupt from the disk I/O subsystem (I/O completed).
8. Save the registers and process state for the other user (if step 6 is executed).
9. Determine that the interrupt was from the disk.
10. Correct the page table and other tables to show that the desired page is
now in memory.
11. Wait for the CPU to be allocated to this process again.
12. Restore the user registers, process state, and new page table, and then
resume the interrupted instruction.
for an instruction probability of having page fault = 1/10000
Hence, probability of having not a page fault = 9999/10000
If TLB hit occurs then memory Access time = 150 +150 = 300(two operand are there) and
if TLB miss occurs then Memory Access Time = Access Page Table1 + Page table2 + Two memory Access =150 + 150 + 150 + 150 = 600
Hit ratio of TLB = 90 %
Memory Access Time = 9999/10000 ( 0.90*300 + 0.10*600 ) + 1/10000( 8000000 + .90*300 + .10*600 )
= 329.967 + 800.033
= 1130 ns
Total Time of execution is = CPU Time + Memory Access Time
Total Time of execution is = 100 ns + 1130 ns = 1230ns
Jul 18, 2019