120 lines
4.9 KiB
Markdown
120 lines
4.9 KiB
Markdown
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This simulator, paging-policy.py, allows you to play around with different
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page-replacement policies. For example, let's examine how LRU performs with a
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series of page references with a cache of size 3:
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0 1 2 0 1 3 0 3 1 2 1
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To do so, run the simulator as follows:
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prompt> ./paging-policy.py --addresses=0,1,2,0,1,3,0,3,1,2,1
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--policy=LRU --cachesize=3 -c
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And what you would see is:
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ARG addresses 0,1,2,0,1,3,0,3,1,2,1
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ARG numaddrs 10
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ARG policy LRU
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ARG cachesize 3
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ARG maxpage 10
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ARG seed 0
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Solving...
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Access: 0 MISS LRU-> [br 0]<-MRU Replace:- [br Hits:0 Misses:1]
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Access: 1 MISS LRU-> [br 0, 1]<-MRU Replace:- [br Hits:0 Misses:2]
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Access: 2 MISS LRU->[br 0, 1, 2]<-MRU Replace:- [br Hits:0 Misses:3]
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Access: 0 HIT LRU->[br 1, 2, 0]<-MRU Replace:- [br Hits:1 Misses:3]
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Access: 1 HIT LRU->[br 2, 0, 1]<-MRU Replace:- [br Hits:2 Misses:3]
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Access: 3 MISS LRU->[br 0, 1, 3]<-MRU Replace:2 [br Hits:2 Misses:4]
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Access: 0 HIT LRU->[br 1, 3, 0]<-MRU Replace:2 [br Hits:3 Misses:4]
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Access: 3 HIT LRU->[br 1, 0, 3]<-MRU Replace:2 [br Hits:4 Misses:4]
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Access: 1 HIT LRU->[br 0, 3, 1]<-MRU Replace:2 [br Hits:5 Misses:4]
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Access: 2 MISS LRU->[br 3, 1, 2]<-MRU Replace:0 [br Hits:5 Misses:5]
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Access: 1 HIT LRU->[br 3, 2, 1]<-MRU Replace:0 [br Hits:6 Misses:5]
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]
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The complete set of possible arguments for paging-policy is listed on the
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following page, and includes a number of options for varying the policy, how
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addresses are specified/generated, and other important parameters such as the
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size of the cache.
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prompt> ./paging-policy.py --help
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Usage: paging-policy.py [options]
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Options:
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-h, --help show this help message and exit
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-a ADDRESSES, --addresses=ADDRESSES
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a set of comma-separated pages to access;
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-1 means randomly generate
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-f ADDRESSFILE, --addressfile=ADDRESSFILE
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a file with a bunch of addresses in it
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-n NUMADDRS, --numaddrs=NUMADDRS
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if -a (--addresses) is -1, this is the
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number of addrs to generate
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-p POLICY, --policy=POLICY
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replacement policy: FIFO, LRU, LFU, OPT,
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UNOPT, RAND, CLOCK
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-b CLOCKBITS, --clockbits=CLOCKBITS
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for CLOCK policy, how many clock bits to use
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-C CACHESIZE, --cachesize=CACHESIZE
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size of the page cache, in pages
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-m MAXPAGE, --maxpage=MAXPAGE
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if randomly generating page accesses,
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this is the max page number
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-s SEED, --seed=SEED random number seed
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-N, --notrace do not print out a detailed trace
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-c, --compute compute answers for me
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]
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As usual, "-c" is used to solve a particular problem, whereas without it, the
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accesses are just listed (and the program does not tell you whether or not a
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particular access is a hit or miss).
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To generate a random problem, instead of using "-a/--addresses" to pass in
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some page references, you can instead pass in "-n/--numaddrs" as the number of
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addresses the program should randomly generate, with "-s/--seed" used to
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specify a different random seed. For example:
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prompt> ./paging-policy.py -s 10 -n 3
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.. .
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Assuming a replacement policy of FIFO, and a cache of size 3 pages,
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figure out whether each of the following page references hit or miss
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in the page cache.
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Access: 5 Hit/Miss? State of Memory?
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Access: 4 Hit/Miss? State of Memory?
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Access: 5 Hit/Miss? State of Memory?
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]
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As you can see, in this example, we specify "-n 3" which means the program
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should generate 3 random page references, which it does: 5, 7, and 5. The
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random seed is also specified (10), which is what gets us those particular
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numbers. After working this out yourself, have the program solve the problem
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for you by passing in the same arguments but with "-c" (showing just the
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relevant part here):
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prompt> ./paging-policy.py -s 10 -n 3 -c
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...
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Solving...
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Access: 5 MISS FirstIn-> [br 5] <-Lastin Replace:- [br Hits:0 Misses:1]
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Access: 4 MISS FirstIn->[br 5, 4] <-Lastin Replace:- [br Hits:0 Misses:2]
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Access: 5 HIT FirstIn->[br 5, 4] <-Lastin Replace:- [br Hits:1 Misses:2]
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]
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The default policy is FIFO, though others are available, including LRU, MRU,
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OPT (the optimal replacement policy, which peeks into the future to see what
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is best to replace), UNOPT (which is the pessimal replacement), RAND (which
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does random replacement), and CLOCK (which does the clock algorithm). The
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CLOCK algorithm also takes another argument (-b), which states how many bits
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should be kept per page; the more clock bits there are, the better the
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algorithm should be at determining which pages to keep in memory.
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Other options include: "-C/--cachesize" which changes the size of the page
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cache; "-m/--maxpage" which is the largest page number that will be used if
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the simulator is generating references for you; and "-f/--addressfile" which
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lets you specify a file with addresses in them, in case you wish to get traces
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from a real application or otherwise use a long trace as input.
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