X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?a=blobdiff_plain;f=TODO;h=53a7060081310488bf1d7f47e4722f2aba11f4cf;hb=edb2693ddd1f451e190a81da0ddda4df845fb246;hp=31606d182661ee33ae3ceefb616355d5f7daac19;hpb=bc0cc9ec385f55e8dee745f55e25d98908255636;p=pintos-anon diff --git a/TODO b/TODO index 31606d1..53a7060 100644 --- a/TODO +++ b/TODO @@ -1,18 +1,184 @@ -*- text -*- -* Miscellaneous: +Godmar says: - - Currently the `pintos' utility has a broken return code policy: it - returns 1 to indicate success. It inherited this mistake from - Bochs, which does something similar. This needs to be fixed. +- 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. -* Userprog project: +- In Project 2, we're missing a test that would fail if they assumed +that contiguous user-virtual addresses are laid out contiguously +in memory. The loading code should ensure that non-contiguous +physical pages are allocated for the data segment (at least.) + +- 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. + +- 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. + +From: "Godmar Back" +Subject: multiple threads waking up at same clock tick +To: "Ben Pfaff" +Date: Wed, 1 Mar 2006 08:14:47 -0500 + +Greg Benson points out another potential TODO item for P1. + +---- +One thing I recall: + +The alarm tests do not test to see if multiple threads are woken up if +their timers have expired. That is, students can write a solution +that just wakes up the first thread on the sleep queue rather than +check for additional threads. Of course, the next thread will be +woken up on the next tick. Also, this might be hard to test. + +--- +Way to test this: (from Godmar Back) + +Thread A with high priority spins until 'ticks' changes, then calls to +timer_sleep(X), Thread B with lower priority is then resumed, calls +set_priority to make its priority equal to that of thread A, then +calls timer_sleep(X), all of that before the next clock interrupt +arrives. + +On wakeup, each thread records wake-up time and calls yield +immediately, forcing the scheduler to switch to the other +equal-priority thread. Both wake-up times must be the same (and match +the planned wake-up time.) + +PS: +I actually tested it and it's hard to pass with the current ips setting. +The bounds on how quickly a thread would need to be able to return after +sleep appear too tight. Need another idea. + +From: "Godmar Back" + +For reasons I don't currently understand, some of our students seem +hesitant to include each thread in a second "all-threads" list and are +looking for ways to implement the advanced scheduler without one. + +Currently, I believe, all tests for the mlfqs are such that all +threads are either ready or sleeping in timer_sleep(). This allows for +an incorrect implementation in which recent-cpu and priorities are +updated only for those threads that are on the alarm list or the ready +list. + +The todo item would be a test where a thread is blocked on a +semaphore, lock or condition variable and have its recent_cpu decay to +zero, and check that it's scheduled right after the unlock/up/signal. + +From: "Godmar Back" +Subject: set_priority & donation - a TODO item +To: "Ben Pfaff" +Date: Mon, 20 Feb 2006 22:20:26 -0500 + +Ben, + +it seems that there are currently no tests that check the proper +behavior of thread_set_priority() when called by a thread that is +running under priority donation. The proper behavior, I assume, is to +temporarily drop the donation if the set priority is higher, and to +reassume the donation should the thread subsequently set its own +priority again to a level that's lower than a still active donation. + + - Godmar + +From: Godmar Back +Subject: project 4 question/comment regarding caching inode data +To: Ben Pfaff +Date: Sat, 14 Jan 2006 15:59:33 -0500 + +Ben, + +in section 6.3.3 in the P4 FAQ, you write: + +"You can store a pointer to inode data in struct inode, if you want," + +Should you point out that if they indeed do that, they likely wouldn't +be able to support more than 64 open inodes systemwide at any given +point in time. + +(This seems like a rather strong limitation; do your current tests +open more than 64 files? +It would also point to an obvious way to make the projects harder by +specifically disallowing that inode data be locked in memory during +the entire time an inode is kept open.) + + - Godmar + +From: Godmar Back +Subject: on caching in project 4 +To: Ben Pfaff +Date: Mon, 9 Jan 2006 20:58:01 -0500 + +here's an idea for future semesters. + +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. - - Move `join' implementation here, from `threads' project, to help - normalize the project difficulties. +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. - - The semantics of the join system call should change so that it - only returns the exit code once. +(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.) + +Godmar Back writes: + +> in your sample solution to P4, dir_reopen does not take any locks when +> changing a directory's open_cnt. This looks like a race condition to +> me, considering that dir_reopen is called from execute_process without +> any filesystem locks held. + +* Get rid of rox--causes more trouble than it's worth + +* Reconsider command line arg style--confuses everyone. + +* Finish writing tour. + +via Godmar Back: + +* Get rid of mmap syscall, add sbrk. + +* page-linear, page-shuffle VM tests do not use enough memory to force + eviction. Should increase memory consumption. + +* Add FS persistence test(s). + +* process_death test needs improvement + +* Internal tests. + +* Improve automatic interpretation of exception messages. + +* Userprog project: - Mark read-only pages as actually read-only in the page table. Or, since this was consistently rated as the easiest project by the @@ -24,9 +190,14 @@ Alternately we could just remove the synchronization on pid selection and check that students fix it. -* Documentation: +* Filesys project: - - Finish writing tour. + - 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: - Add "Digging Deeper" sections that describe the nitty-gritty x86 details for the benefit of those interested. @@ -40,23 +211,73 @@ . Low-level x86 stuff, like paged page tables. + . Specifics on how to implement sbrk, malloc. + . Other good ideas. - - mmap/munmap should use segment IDs like Nachos. Too hard - otherwise. + . opendir/readdir/closedir + + . 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: - - Add src/testcases/vm, src/testcases/filesys and make it clear to use - them? +- 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.