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CSE451 – Section 7

CSE451 – Section 7. Usual stuff. Project 3 will be due Monday the 27 th Experiment design email to TAs: By midnight on Sunday the 19th Today: Project 3 overview. Project 3. Given: vmtrace Simulates virtual memory on a memory trace file

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CSE451 – Section 7

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  1. CSE451 – Section 7

  2. Usual stuff • Project 3 will be due Monday the 27th • Experiment design email to TAs: By midnight on Sunday the 19th • Today: • Project 3 overview

  3. Project 3 • Given: vmtrace • Simulates virtual memory on a memory trace file • Tracefile = a list of all VA references during execution • Includes: instruction fetch, load, store references • Takes in: • a memory trace file (given, netscape.exe.et.gz) • physical memory size • page size • Outputs: • # of memory references • # of page faults • compulsory faults • page evictions • pageouts

  4. vmtrace help barb% ./vmtrace -h Usage: vmtrace [OPTIONS] ALGORITHM [TRACEFILE|-] Process TRACEFILE, simulating a VM system. Reports stats on paging behavior. Zlib is available; input may be compressed. If TRACEFILE is not specified or is '-', input will be taken from stdin. ALGORITHM specifies the fault handler, and should be one of: random Options: -h|--help Print this message and exit. -V|--version Print the version information. -v|--verbose Verbose output. Includes progress output. -t|--test Run self tests. -o FILE|--output=FILE Append statistics output to the given file. -l REFS|--limit=REFS Stop after first REFS refs. -p PAGES|--pages=PAGES Simulate PAGES physical pages. Minimum value 4. -s SIZE|--size=SIZE Simulate a page size of SIZE bytes. Size must be a power of 2. barb%

  5. vmtrace example output barb% ./vmtrace -l 10000 -v random netscape.exe.et.gz vmtrace: using replacement algorithm 'random' vmtrace: reading from netscape.exe.et.gz vmtrace: reached 10000 references phys_pages,pagesize,input_file,fault_handler,ref_limit 128,1024,netscape.exe.et.gz,random,10000 type,code,load,store references,6171,1905,1924 miss,62,48,23 compulsory,53,43,21 evictions,27,16,4 pagetouts,9,7,1 barb%

  6. P3 Goals • Implement some page replacement algorithms • Design and perform an experiment on some aspect of virtual memory • Important to pick a good topic, ask us if not sure! • This is why we ask for your design midway through

  7. Your job: Replacement Algorithms • Given: • random • You need to write: • FIFO • LRU Clock • One of your choice • A few possibilities: • True LRU (e.g. via storing full timestamp) • Variations on LRU Clock (enhanced second-chance, etc) • LFU/MFU • Your own! • You can write more than 3 if your experiment focuses on replacement algorithms.

  8. Source code… fault.h /* fault handlers are functions that return nothing (void) and * take 2 arguments: a pte_t* and a ref_kind_t. * The pte is the new page that must be inserted, and the * type is for statistical reporting. */ typedef void (*fault_handler_t)(pte_t *pte, ref_kind_t type); /* fault_handler_info_t lets us match the actual function to a * name. fault_handlers is searched by options.c to locate the * handler named on the command line. */ typedef struct _fault_handler_info { char *name; fault_handler_t handler; } fault_handler_info_t;

  9. Source code… fault.c fault_handler_info_t fault_handlers[2] = { { "random", fault_random }, { NULL, NULL } /* last entry must always be NULL/NULL */ }; void fault_random(pte_t *pte, ref_kind_t type) { int page; page = random() % opts.phys_pages; physmem_evict(page, type); physmem_load(page, pte, type); } Next: add your own handlers!

  10. Your job: Project 3 experiment • Have a hypothesis • “Algorithm y is better than algorithm x” • “Big pages are better” • “Prefetching will reduce the number of page faults” • “If we understand why x happens, we can fix it” • Explain why you think it will turn out that way • Two steps • Determine baseline behavior • New test • Change one aspect of the system, observe differences

  11. experiment ideas • Good: • What is the ideal page size for this trace under different amounts of main memory? • Compare performance of various replacement algorithms. How much better/worse is page replacement algorithm X than Y? • Compare “real” LRU and LRU clock, FIFO, etc • How close can we come to LRU without doing any work between page faults? • No scanning, constant work per page fault • How important is recency vs. frequency in predicting page re-use? • Not so good: • What kind of music is made when I convert the address trace to notes? • Can I make a fractal out of this data?

  12. Tips • vmtrace is not an execution simulation • You control what happens on a page fault • You control what happens on a memory access • You can modify formats for PTE, page, etc • Refresh your scripting skills • vmtrace is very CPU-intensive • forkbomb: PIII-800/256MB • Find faster machines (such as Linux boxes in the lab) • Copy the trace file to local machine • Full trace can take hours to execute!

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