X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?a=blobdiff_plain;f=TODO;h=38836157fc052fe3a07b91d5d03bea94c64ac104;hb=ca445c5de2cc3e9b57ab1b44a00188dbff54ebe1;hp=9825200fed911631d245c7fa0048ee61476789fb;hpb=e2c7fa52b1352b6fe736050e30c3a9a9ad633307;p=pintos-anon diff --git a/TODO b/TODO index 9825200..3883615 100644 --- a/TODO +++ b/TODO @@ -1,73 +1,88 @@ -*- text -*- -* The tests in tests/ don't apply the grading patches. +Godmar says: -* We need better example programs. +- In Project 2, we're missing tests that pass arguments to system calls +that span multiple pages, where some are mapped and some are not. +An implementation that only checks the first page, rather than all pages +that can be touched during a call to read()/write() passes all tests. - - Need an mmap example program as a replacement for the crappy mmap FAQ - question. +- Need some tests that test that illegal accesses lead to process +termination. I have written some, will add them. In P2, obviously, +this would require that the students break this functionality since +the page directory is initialized for them, still it would be good +to have. -* Threads: +- There does not appear to be a test that checks that they close all +fd's on exit. Idea: add statistics & self-diagnostics code to palloc.c +and malloc.c. Self-diagnostics code could be used for debugging. +The statistics code would report how much kernel memory is free. +Add a system call "get_kernel_memory_information". User programs +could engage in a variety of activities and notice leaks by checking +the kernel memory statistics. - - join-invalid doesn't compile if tid_t is not scalar type. +From: Godmar Back +Subject: on caching in project 4 +To: Ben Pfaff +Date: Mon, 9 Jan 2006 20:58:01 -0500 - - mlfqs tests suck. They aren't even correct, e.g. the amarv - submission from win0405 is graded incorrectly. +here's an idea for future semesters. -* Userprog project: +I'm in the middle of project 4, I've started by implementing a buffer +cache and plugging it into the existing filesystem. Along the way I +was wondering how we could test the cache. - - Don't emphasize that stuff needs to be copied from user space to - kernel space. Instead, emphasize validation and suggest that - copying is a common solution and that it will be necessary in - project 3 and in real OSes. Also revise the grading criteria to - match. +Maybe one could adopt a similar testing strategy as in project 1 for +the MLQFS scheduler: add a function that reads "get_cache_accesses()" +and a function "get_cache_hits()". Then create a version of pintos +that creates access traces for a to-be-determined workload. Run an +off-line analysis that would determine how many hits a perfect cache +would have (MAX), and how much say an LRU strategy would give (MIN). +Then add a fudge factor to account for different index strategies and +test that the reported number of cache hits/accesses is within (MIN, +MAX) +/- fudge factor. - - Move `join' implementation here, from `threads' project, to help - normalize the project difficulties. +(As an aside - I am curious why you chose to use a clock-style +algorithm rather than the more straightforward LRU for your buffer +cache implementation in your sample solution. Is there a reason for +that? I was curious to see if it made a difference, so I implemented +LRU for your cache implementation and ran the test workload of project +4 and printed cache hits/accesses. +I found that for that workload, the clock-based algorithm performs +almost identical to LRU (within about 1%, but I ran nondeterministally +with QEMU). I then reduced the cache size to 32 blocks and found again +the same performance, which raises the suspicion that the test +workload might not force any cache replacement, so the eviction +strategy doesn't matter.) - - The semantics of the join system call should change so that it - only returns the exit code once. +* Get rid of rox--causes more trouble than it's worth - - Mark read-only pages as actually read-only in the page table. Or, - since this was consistently rated as the easiest project by the - students, require them to do it. +* Reconsider command line arg style--confuses everyone. - - Don't provide per-process pagedir implementation but only - single-process implementation and require students to implement - the separation? This project was rated as the easiest after all. - Alternately we could just remove the synchronization on pid - selection and check that students fix it. +* Finish writing tour. -* VM project: +via Godmar Back: - - Discuss the perils of mixing dirty bits between kernel and user virtual - memory. +* Get rid of mmap syscall, add sbrk. - - Sample solution. +* page-linear, page-shuffle VM tests do not use enough memory to force + eviction. Should increase memory consumption. - - Update grading/vm to reflect new mmap, munmap forms. +* Add FS persistence test(s). -* Filesys project: - - - Increase maximum disk size from 8 MB to something that actually - requires doubly indirect nodes. There is a negative pressure here - from the bitmap object--perhaps we need a specialized bitmap that - doesn't have to be all in-memory at once. - - Alternatively, shrink the inode size. +* process_death test needs improvement - - Add mkdir and ls example user programs. +* Internal tests. - - Add option to disable buffer cache. - - - Get rid of "dump" commands--they're not really useful. +* Filesys project: - - Sample solution. + - Need a better way to measure performance improvement of buffer + cache. Some students reported that their system was slower with + cache--likely, Bochs doesn't simulate a disk with a realistic + speed. * Documentation: - - Finish writing tour. - - Add "Digging Deeper" sections that describe the nitty-gritty x86 details for the benefit of those interested. @@ -78,24 +93,71 @@ - Add extra credit: - . Low-level x86 stuff, like paged page tables. - . Specifics on how to implement sbrk, malloc. . Other good ideas. - - Add src/testcases/vm, src/testcases/filesys and make it clear to use - them? + . everything needed for getcwd() + +To add partition support: + +- Find four partition types that are more or less unused and choose to + use them for Pintos. (This is implemented.) + +- Bootloader reads partition tables of all BIOS devices to find the + first that has the "Pintos kernel" partition type. (This is + implemented.) Ideally the bootloader would make sure there is + exactly one such partition, but I didn't implement that yet. + +- Bootloader reads kernel into memory at 1 MB using BIOS calls. (This + is implemented.) + +- Kernel arguments have to go into a separate sector because the + bootloader is otherwise too big to fit now? (I don't recall if I + did anything about this.) + +- Kernel at boot also scans partition tables of all the disks it can + find to find the ones with the four Pintos partition types (perhaps + not all exist). After that, it makes them available to the rest of + the kernel (and doesn't allow access to other devices, for safety). + +- "pintos" and "pintos-mkdisk" need to write a partition table to the + disks that they create. "pintos-mkdisk" will need to take a new + parameter specifying the type. (I might have partially implemented + this, don't remember.) + +- "pintos" should insist on finding a partition header on disks handed + to it, for safety. + +- Need some way for "pintos" to assemble multiple disks or partitions + into a single image that can be copied directly to a USB block + device. (I don't know whether I came up with a good solution yet or + not, or whether I implemented any of it.) + +To add USB support: + +- Needs to be able to scan PCI bus for UHCI controller. (I + implemented this partially.) -* Tests: +- May want to be able to initialize USB controllers over CardBus + bridges. I don't know whether this requires additional work or if + it's useful enough to warrant extra work. (It's of special interest + for me because I have a laptop that only has USB via CardBus.) - - Release some of them. +- There are many protocol layers involved: SCSI over USB-Mass Storage + over USB over UHCI over PCI. (I may be forgetting one.) I don't + know yet whether it's best to separate the layers or to merge (some + of) them. I think that a simple and clean organization should be a + priority. - - The threads, userprog, vm test source files could use - factorization and cleanup along the lines of fslib in the filesys - tests. +- VMware can likely be used for testing because it can expose host USB + devices as guest USB devices. This is safer and more convenient + than using real hardware for testing. - - The p1-4.c testcase needs significant tuning. Currently it takes - too long (especially when SHOW_PROGRESS is turned on) and doesn't - show significant improvement. +- Should test with a variety of USB keychain devices because there + seems to be wide variation among them, especially in the SCSI + protocols they support. Should try to use a "lowest-common + denominator" SCSI protocol if any such thing really exists. +- Might want to add a feature whereby kernel arguments can be given + interactively, rather than passed on-disk. Needs some though.